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linux/arch/x86/kernel/cpu/bugs.c
Johannes Wikner c62fa117c3 x86/bugs: Do not use UNTRAIN_RET with IBPB on entry 
Since X86_FEATURE_ENTRY_IBPB will invalidate all harmful predictions
with IBPB, no software-based untraining of returns is needed anymore.
Currently, this change affects retbleed and SRSO mitigations so if
either of the mitigations is doing IBPB and the other one does the
software sequence, the latter is not needed anymore.

  [ bp: Massage commit message. ]

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Johannes Wikner <kwikner@ethz.ch>
Cc: <stable@kernel.org>
2024-10-10 10:38:21 +02:00

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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 1994 Linus Torvalds
*
* Cyrix stuff, June 1998 by:
* - Rafael R. Reilova (moved everything from head.S),
* <rreilova@ececs.uc.edu>
* - Channing Corn (tests & fixes),
* - Andrew D. Balsa (code cleanup).
*/
#include <linux/init.h>
#include <linux/cpu.h>
#include <linux/module.h>
#include <linux/nospec.h>
#include <linux/prctl.h>
#include <linux/sched/smt.h>
#include <linux/pgtable.h>
#include <linux/bpf.h>
#include <asm/spec-ctrl.h>
#include <asm/cmdline.h>
#include <asm/bugs.h>
#include <asm/processor.h>
#include <asm/processor-flags.h>
#include <asm/fpu/api.h>
#include <asm/msr.h>
#include <asm/vmx.h>
#include <asm/paravirt.h>
#include <asm/cpu_device_id.h>
#include <asm/e820/api.h>
#include <asm/hypervisor.h>
#include <asm/tlbflush.h>
#include <asm/cpu.h>
#include "cpu.h"
static void __init spectre_v1_select_mitigation(void);
static void __init spectre_v2_select_mitigation(void);
static void __init retbleed_select_mitigation(void);
static void __init spectre_v2_user_select_mitigation(void);
static void __init ssb_select_mitigation(void);
static void __init l1tf_select_mitigation(void);
static void __init mds_select_mitigation(void);
static void __init md_clear_update_mitigation(void);
static void __init md_clear_select_mitigation(void);
static void __init taa_select_mitigation(void);
static void __init mmio_select_mitigation(void);
static void __init srbds_select_mitigation(void);
static void __init l1d_flush_select_mitigation(void);
static void __init srso_select_mitigation(void);
static void __init gds_select_mitigation(void);
/* The base value of the SPEC_CTRL MSR without task-specific bits set */
u64 x86_spec_ctrl_base;
EXPORT_SYMBOL_GPL(x86_spec_ctrl_base);
/* The current value of the SPEC_CTRL MSR with task-specific bits set */
DEFINE_PER_CPU(u64, x86_spec_ctrl_current);
EXPORT_PER_CPU_SYMBOL_GPL(x86_spec_ctrl_current);
u64 x86_pred_cmd __ro_after_init = PRED_CMD_IBPB;
EXPORT_SYMBOL_GPL(x86_pred_cmd);
static u64 __ro_after_init x86_arch_cap_msr;
static DEFINE_MUTEX(spec_ctrl_mutex);
void (*x86_return_thunk)(void) __ro_after_init = __x86_return_thunk;
/* Update SPEC_CTRL MSR and its cached copy unconditionally */
static void update_spec_ctrl(u64 val)
{
this_cpu_write(x86_spec_ctrl_current, val);
wrmsrl(MSR_IA32_SPEC_CTRL, val);
}
/*
* Keep track of the SPEC_CTRL MSR value for the current task, which may differ
* from x86_spec_ctrl_base due to STIBP/SSB in __speculation_ctrl_update().
*/
void update_spec_ctrl_cond(u64 val)
{
if (this_cpu_read(x86_spec_ctrl_current) == val)
return;
this_cpu_write(x86_spec_ctrl_current, val);
/*
* When KERNEL_IBRS this MSR is written on return-to-user, unless
* forced the update can be delayed until that time.
*/
if (!cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS))
wrmsrl(MSR_IA32_SPEC_CTRL, val);
}
noinstr u64 spec_ctrl_current(void)
{
return this_cpu_read(x86_spec_ctrl_current);
}
EXPORT_SYMBOL_GPL(spec_ctrl_current);
/*
* AMD specific MSR info for Speculative Store Bypass control.
* x86_amd_ls_cfg_ssbd_mask is initialized in identify_boot_cpu().
*/
u64 __ro_after_init x86_amd_ls_cfg_base;
u64 __ro_after_init x86_amd_ls_cfg_ssbd_mask;
/* Control conditional STIBP in switch_to() */
DEFINE_STATIC_KEY_FALSE(switch_to_cond_stibp);
/* Control conditional IBPB in switch_mm() */
DEFINE_STATIC_KEY_FALSE(switch_mm_cond_ibpb);
/* Control unconditional IBPB in switch_mm() */
DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb);
/* Control MDS CPU buffer clear before idling (halt, mwait) */
DEFINE_STATIC_KEY_FALSE(mds_idle_clear);
EXPORT_SYMBOL_GPL(mds_idle_clear);
/*
* Controls whether l1d flush based mitigations are enabled,
* based on hw features and admin setting via boot parameter
* defaults to false
*/
DEFINE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush);
/* Controls CPU Fill buffer clear before KVM guest MMIO accesses */
DEFINE_STATIC_KEY_FALSE(mmio_stale_data_clear);
EXPORT_SYMBOL_GPL(mmio_stale_data_clear);
void __init cpu_select_mitigations(void)
{
/*
* Read the SPEC_CTRL MSR to account for reserved bits which may
* have unknown values. AMD64_LS_CFG MSR is cached in the early AMD
* init code as it is not enumerated and depends on the family.
*/
if (cpu_feature_enabled(X86_FEATURE_MSR_SPEC_CTRL)) {
rdmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
/*
* Previously running kernel (kexec), may have some controls
* turned ON. Clear them and let the mitigations setup below
* rediscover them based on configuration.
*/
x86_spec_ctrl_base &= ~SPEC_CTRL_MITIGATIONS_MASK;
}
x86_arch_cap_msr = x86_read_arch_cap_msr();
/* Select the proper CPU mitigations before patching alternatives: */
spectre_v1_select_mitigation();
spectre_v2_select_mitigation();
/*
* retbleed_select_mitigation() relies on the state set by
* spectre_v2_select_mitigation(); specifically it wants to know about
* spectre_v2=ibrs.
*/
retbleed_select_mitigation();
/*
* spectre_v2_user_select_mitigation() relies on the state set by
* retbleed_select_mitigation(); specifically the STIBP selection is
* forced for UNRET or IBPB.
*/
spectre_v2_user_select_mitigation();
ssb_select_mitigation();
l1tf_select_mitigation();
md_clear_select_mitigation();
srbds_select_mitigation();
l1d_flush_select_mitigation();
/*
* srso_select_mitigation() depends and must run after
* retbleed_select_mitigation().
*/
srso_select_mitigation();
gds_select_mitigation();
}
/*
* NOTE: This function is *only* called for SVM, since Intel uses
* MSR_IA32_SPEC_CTRL for SSBD.
*/
void
x86_virt_spec_ctrl(u64 guest_virt_spec_ctrl, bool setguest)
{
u64 guestval, hostval;
struct thread_info *ti = current_thread_info();
/*
* If SSBD is not handled in MSR_SPEC_CTRL on AMD, update
* MSR_AMD64_L2_CFG or MSR_VIRT_SPEC_CTRL if supported.
*/
if (!static_cpu_has(X86_FEATURE_LS_CFG_SSBD) &&
!static_cpu_has(X86_FEATURE_VIRT_SSBD))
return;
/*
* If the host has SSBD mitigation enabled, force it in the host's
* virtual MSR value. If its not permanently enabled, evaluate
* current's TIF_SSBD thread flag.
*/
if (static_cpu_has(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE))
hostval = SPEC_CTRL_SSBD;
else
hostval = ssbd_tif_to_spec_ctrl(ti->flags);
/* Sanitize the guest value */
guestval = guest_virt_spec_ctrl & SPEC_CTRL_SSBD;
if (hostval != guestval) {
unsigned long tif;
tif = setguest ? ssbd_spec_ctrl_to_tif(guestval) :
ssbd_spec_ctrl_to_tif(hostval);
speculation_ctrl_update(tif);
}
}
EXPORT_SYMBOL_GPL(x86_virt_spec_ctrl);
static void x86_amd_ssb_disable(void)
{
u64 msrval = x86_amd_ls_cfg_base | x86_amd_ls_cfg_ssbd_mask;
if (boot_cpu_has(X86_FEATURE_VIRT_SSBD))
wrmsrl(MSR_AMD64_VIRT_SPEC_CTRL, SPEC_CTRL_SSBD);
else if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD))
wrmsrl(MSR_AMD64_LS_CFG, msrval);
}
#undef pr_fmt
#define pr_fmt(fmt) "MDS: " fmt
/* Default mitigation for MDS-affected CPUs */
static enum mds_mitigations mds_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_MDS) ? MDS_MITIGATION_FULL : MDS_MITIGATION_OFF;
static bool mds_nosmt __ro_after_init = false;
static const char * const mds_strings[] = {
[MDS_MITIGATION_OFF] = "Vulnerable",
[MDS_MITIGATION_FULL] = "Mitigation: Clear CPU buffers",
[MDS_MITIGATION_VMWERV] = "Vulnerable: Clear CPU buffers attempted, no microcode",
};
static void __init mds_select_mitigation(void)
{
if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off()) {
mds_mitigation = MDS_MITIGATION_OFF;
return;
}
if (mds_mitigation == MDS_MITIGATION_FULL) {
if (!boot_cpu_has(X86_FEATURE_MD_CLEAR))
mds_mitigation = MDS_MITIGATION_VMWERV;
setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
if (!boot_cpu_has(X86_BUG_MSBDS_ONLY) &&
(mds_nosmt || cpu_mitigations_auto_nosmt()))
cpu_smt_disable(false);
}
}
static int __init mds_cmdline(char *str)
{
if (!boot_cpu_has_bug(X86_BUG_MDS))
return 0;
if (!str)
return -EINVAL;
if (!strcmp(str, "off"))
mds_mitigation = MDS_MITIGATION_OFF;
else if (!strcmp(str, "full"))
mds_mitigation = MDS_MITIGATION_FULL;
else if (!strcmp(str, "full,nosmt")) {
mds_mitigation = MDS_MITIGATION_FULL;
mds_nosmt = true;
}
return 0;
}
early_param("mds", mds_cmdline);
#undef pr_fmt
#define pr_fmt(fmt) "TAA: " fmt
enum taa_mitigations {
TAA_MITIGATION_OFF,
TAA_MITIGATION_UCODE_NEEDED,
TAA_MITIGATION_VERW,
TAA_MITIGATION_TSX_DISABLED,
};
/* Default mitigation for TAA-affected CPUs */
static enum taa_mitigations taa_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_TAA) ? TAA_MITIGATION_VERW : TAA_MITIGATION_OFF;
static bool taa_nosmt __ro_after_init;
static const char * const taa_strings[] = {
[TAA_MITIGATION_OFF] = "Vulnerable",
[TAA_MITIGATION_UCODE_NEEDED] = "Vulnerable: Clear CPU buffers attempted, no microcode",
[TAA_MITIGATION_VERW] = "Mitigation: Clear CPU buffers",
[TAA_MITIGATION_TSX_DISABLED] = "Mitigation: TSX disabled",
};
static void __init taa_select_mitigation(void)
{
if (!boot_cpu_has_bug(X86_BUG_TAA)) {
taa_mitigation = TAA_MITIGATION_OFF;
return;
}
/* TSX previously disabled by tsx=off */
if (!boot_cpu_has(X86_FEATURE_RTM)) {
taa_mitigation = TAA_MITIGATION_TSX_DISABLED;
return;
}
if (cpu_mitigations_off()) {
taa_mitigation = TAA_MITIGATION_OFF;
return;
}
/*
* TAA mitigation via VERW is turned off if both
* tsx_async_abort=off and mds=off are specified.
*/
if (taa_mitigation == TAA_MITIGATION_OFF &&
mds_mitigation == MDS_MITIGATION_OFF)
return;
if (boot_cpu_has(X86_FEATURE_MD_CLEAR))
taa_mitigation = TAA_MITIGATION_VERW;
else
taa_mitigation = TAA_MITIGATION_UCODE_NEEDED;
/*
* VERW doesn't clear the CPU buffers when MD_CLEAR=1 and MDS_NO=1.
* A microcode update fixes this behavior to clear CPU buffers. It also
* adds support for MSR_IA32_TSX_CTRL which is enumerated by the
* ARCH_CAP_TSX_CTRL_MSR bit.
*
* On MDS_NO=1 CPUs if ARCH_CAP_TSX_CTRL_MSR is not set, microcode
* update is required.
*/
if ( (x86_arch_cap_msr & ARCH_CAP_MDS_NO) &&
!(x86_arch_cap_msr & ARCH_CAP_TSX_CTRL_MSR))
taa_mitigation = TAA_MITIGATION_UCODE_NEEDED;
/*
* TSX is enabled, select alternate mitigation for TAA which is
* the same as MDS. Enable MDS static branch to clear CPU buffers.
*
* For guests that can't determine whether the correct microcode is
* present on host, enable the mitigation for UCODE_NEEDED as well.
*/
setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
if (taa_nosmt || cpu_mitigations_auto_nosmt())
cpu_smt_disable(false);
}
static int __init tsx_async_abort_parse_cmdline(char *str)
{
if (!boot_cpu_has_bug(X86_BUG_TAA))
return 0;
if (!str)
return -EINVAL;
if (!strcmp(str, "off")) {
taa_mitigation = TAA_MITIGATION_OFF;
} else if (!strcmp(str, "full")) {
taa_mitigation = TAA_MITIGATION_VERW;
} else if (!strcmp(str, "full,nosmt")) {
taa_mitigation = TAA_MITIGATION_VERW;
taa_nosmt = true;
}
return 0;
}
early_param("tsx_async_abort", tsx_async_abort_parse_cmdline);
#undef pr_fmt
#define pr_fmt(fmt) "MMIO Stale Data: " fmt
enum mmio_mitigations {
MMIO_MITIGATION_OFF,
MMIO_MITIGATION_UCODE_NEEDED,
MMIO_MITIGATION_VERW,
};
/* Default mitigation for Processor MMIO Stale Data vulnerabilities */
static enum mmio_mitigations mmio_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_MMIO_STALE_DATA) ? MMIO_MITIGATION_VERW : MMIO_MITIGATION_OFF;
static bool mmio_nosmt __ro_after_init = false;
static const char * const mmio_strings[] = {
[MMIO_MITIGATION_OFF] = "Vulnerable",
[MMIO_MITIGATION_UCODE_NEEDED] = "Vulnerable: Clear CPU buffers attempted, no microcode",
[MMIO_MITIGATION_VERW] = "Mitigation: Clear CPU buffers",
};
static void __init mmio_select_mitigation(void)
{
if (!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA) ||
boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN) ||
cpu_mitigations_off()) {
mmio_mitigation = MMIO_MITIGATION_OFF;
return;
}
if (mmio_mitigation == MMIO_MITIGATION_OFF)
return;
/*
* Enable CPU buffer clear mitigation for host and VMM, if also affected
* by MDS or TAA. Otherwise, enable mitigation for VMM only.
*/
if (boot_cpu_has_bug(X86_BUG_MDS) || (boot_cpu_has_bug(X86_BUG_TAA) &&
boot_cpu_has(X86_FEATURE_RTM)))
setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
/*
* X86_FEATURE_CLEAR_CPU_BUF could be enabled by other VERW based
* mitigations, disable KVM-only mitigation in that case.
*/
if (boot_cpu_has(X86_FEATURE_CLEAR_CPU_BUF))
static_branch_disable(&mmio_stale_data_clear);
else
static_branch_enable(&mmio_stale_data_clear);
/*
* If Processor-MMIO-Stale-Data bug is present and Fill Buffer data can
* be propagated to uncore buffers, clearing the Fill buffers on idle
* is required irrespective of SMT state.
*/
if (!(x86_arch_cap_msr & ARCH_CAP_FBSDP_NO))
static_branch_enable(&mds_idle_clear);
/*
* Check if the system has the right microcode.
*
* CPU Fill buffer clear mitigation is enumerated by either an explicit
* FB_CLEAR or by the presence of both MD_CLEAR and L1D_FLUSH on MDS
* affected systems.
*/
if ((x86_arch_cap_msr & ARCH_CAP_FB_CLEAR) ||
(boot_cpu_has(X86_FEATURE_MD_CLEAR) &&
boot_cpu_has(X86_FEATURE_FLUSH_L1D) &&
!(x86_arch_cap_msr & ARCH_CAP_MDS_NO)))
mmio_mitigation = MMIO_MITIGATION_VERW;
else
mmio_mitigation = MMIO_MITIGATION_UCODE_NEEDED;
if (mmio_nosmt || cpu_mitigations_auto_nosmt())
cpu_smt_disable(false);
}
static int __init mmio_stale_data_parse_cmdline(char *str)
{
if (!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA))
return 0;
if (!str)
return -EINVAL;
if (!strcmp(str, "off")) {
mmio_mitigation = MMIO_MITIGATION_OFF;
} else if (!strcmp(str, "full")) {
mmio_mitigation = MMIO_MITIGATION_VERW;
} else if (!strcmp(str, "full,nosmt")) {
mmio_mitigation = MMIO_MITIGATION_VERW;
mmio_nosmt = true;
}
return 0;
}
early_param("mmio_stale_data", mmio_stale_data_parse_cmdline);
#undef pr_fmt
#define pr_fmt(fmt) "Register File Data Sampling: " fmt
enum rfds_mitigations {
RFDS_MITIGATION_OFF,
RFDS_MITIGATION_VERW,
RFDS_MITIGATION_UCODE_NEEDED,
};
/* Default mitigation for Register File Data Sampling */
static enum rfds_mitigations rfds_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_RFDS) ? RFDS_MITIGATION_VERW : RFDS_MITIGATION_OFF;
static const char * const rfds_strings[] = {
[RFDS_MITIGATION_OFF] = "Vulnerable",
[RFDS_MITIGATION_VERW] = "Mitigation: Clear Register File",
[RFDS_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode",
};
static void __init rfds_select_mitigation(void)
{
if (!boot_cpu_has_bug(X86_BUG_RFDS) || cpu_mitigations_off()) {
rfds_mitigation = RFDS_MITIGATION_OFF;
return;
}
if (rfds_mitigation == RFDS_MITIGATION_OFF)
return;
if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR)
setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
else
rfds_mitigation = RFDS_MITIGATION_UCODE_NEEDED;
}
static __init int rfds_parse_cmdline(char *str)
{
if (!str)
return -EINVAL;
if (!boot_cpu_has_bug(X86_BUG_RFDS))
return 0;
if (!strcmp(str, "off"))
rfds_mitigation = RFDS_MITIGATION_OFF;
else if (!strcmp(str, "on"))
rfds_mitigation = RFDS_MITIGATION_VERW;
return 0;
}
early_param("reg_file_data_sampling", rfds_parse_cmdline);
#undef pr_fmt
#define pr_fmt(fmt) "" fmt
static void __init md_clear_update_mitigation(void)
{
if (cpu_mitigations_off())
return;
if (!boot_cpu_has(X86_FEATURE_CLEAR_CPU_BUF))
goto out;
/*
* X86_FEATURE_CLEAR_CPU_BUF is now enabled. Update MDS, TAA and MMIO
* Stale Data mitigation, if necessary.
*/
if (mds_mitigation == MDS_MITIGATION_OFF &&
boot_cpu_has_bug(X86_BUG_MDS)) {
mds_mitigation = MDS_MITIGATION_FULL;
mds_select_mitigation();
}
if (taa_mitigation == TAA_MITIGATION_OFF &&
boot_cpu_has_bug(X86_BUG_TAA)) {
taa_mitigation = TAA_MITIGATION_VERW;
taa_select_mitigation();
}
/*
* MMIO_MITIGATION_OFF is not checked here so that mmio_stale_data_clear
* gets updated correctly as per X86_FEATURE_CLEAR_CPU_BUF state.
*/
if (boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) {
mmio_mitigation = MMIO_MITIGATION_VERW;
mmio_select_mitigation();
}
if (rfds_mitigation == RFDS_MITIGATION_OFF &&
boot_cpu_has_bug(X86_BUG_RFDS)) {
rfds_mitigation = RFDS_MITIGATION_VERW;
rfds_select_mitigation();
}
out:
if (boot_cpu_has_bug(X86_BUG_MDS))
pr_info("MDS: %s\n", mds_strings[mds_mitigation]);
if (boot_cpu_has_bug(X86_BUG_TAA))
pr_info("TAA: %s\n", taa_strings[taa_mitigation]);
if (boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA))
pr_info("MMIO Stale Data: %s\n", mmio_strings[mmio_mitigation]);
else if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN))
pr_info("MMIO Stale Data: Unknown: No mitigations\n");
if (boot_cpu_has_bug(X86_BUG_RFDS))
pr_info("Register File Data Sampling: %s\n", rfds_strings[rfds_mitigation]);
}
static void __init md_clear_select_mitigation(void)
{
mds_select_mitigation();
taa_select_mitigation();
mmio_select_mitigation();
rfds_select_mitigation();
/*
* As these mitigations are inter-related and rely on VERW instruction
* to clear the microarchitural buffers, update and print their status
* after mitigation selection is done for each of these vulnerabilities.
*/
md_clear_update_mitigation();
}
#undef pr_fmt
#define pr_fmt(fmt) "SRBDS: " fmt
enum srbds_mitigations {
SRBDS_MITIGATION_OFF,
SRBDS_MITIGATION_UCODE_NEEDED,
SRBDS_MITIGATION_FULL,
SRBDS_MITIGATION_TSX_OFF,
SRBDS_MITIGATION_HYPERVISOR,
};
static enum srbds_mitigations srbds_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_SRBDS) ? SRBDS_MITIGATION_FULL : SRBDS_MITIGATION_OFF;
static const char * const srbds_strings[] = {
[SRBDS_MITIGATION_OFF] = "Vulnerable",
[SRBDS_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode",
[SRBDS_MITIGATION_FULL] = "Mitigation: Microcode",
[SRBDS_MITIGATION_TSX_OFF] = "Mitigation: TSX disabled",
[SRBDS_MITIGATION_HYPERVISOR] = "Unknown: Dependent on hypervisor status",
};
static bool srbds_off;
void update_srbds_msr(void)
{
u64 mcu_ctrl;
if (!boot_cpu_has_bug(X86_BUG_SRBDS))
return;
if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
return;
if (srbds_mitigation == SRBDS_MITIGATION_UCODE_NEEDED)
return;
/*
* A MDS_NO CPU for which SRBDS mitigation is not needed due to TSX
* being disabled and it hasn't received the SRBDS MSR microcode.
*/
if (!boot_cpu_has(X86_FEATURE_SRBDS_CTRL))
return;
rdmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl);
switch (srbds_mitigation) {
case SRBDS_MITIGATION_OFF:
case SRBDS_MITIGATION_TSX_OFF:
mcu_ctrl |= RNGDS_MITG_DIS;
break;
case SRBDS_MITIGATION_FULL:
mcu_ctrl &= ~RNGDS_MITG_DIS;
break;
default:
break;
}
wrmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl);
}
static void __init srbds_select_mitigation(void)
{
if (!boot_cpu_has_bug(X86_BUG_SRBDS))
return;
/*
* Check to see if this is one of the MDS_NO systems supporting TSX that
* are only exposed to SRBDS when TSX is enabled or when CPU is affected
* by Processor MMIO Stale Data vulnerability.
*/
if ((x86_arch_cap_msr & ARCH_CAP_MDS_NO) && !boot_cpu_has(X86_FEATURE_RTM) &&
!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA))
srbds_mitigation = SRBDS_MITIGATION_TSX_OFF;
else if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
srbds_mitigation = SRBDS_MITIGATION_HYPERVISOR;
else if (!boot_cpu_has(X86_FEATURE_SRBDS_CTRL))
srbds_mitigation = SRBDS_MITIGATION_UCODE_NEEDED;
else if (cpu_mitigations_off() || srbds_off)
srbds_mitigation = SRBDS_MITIGATION_OFF;
update_srbds_msr();
pr_info("%s\n", srbds_strings[srbds_mitigation]);
}
static int __init srbds_parse_cmdline(char *str)
{
if (!str)
return -EINVAL;
if (!boot_cpu_has_bug(X86_BUG_SRBDS))
return 0;
srbds_off = !strcmp(str, "off");
return 0;
}
early_param("srbds", srbds_parse_cmdline);
#undef pr_fmt
#define pr_fmt(fmt) "L1D Flush : " fmt
enum l1d_flush_mitigations {
L1D_FLUSH_OFF = 0,
L1D_FLUSH_ON,
};
static enum l1d_flush_mitigations l1d_flush_mitigation __initdata = L1D_FLUSH_OFF;
static void __init l1d_flush_select_mitigation(void)
{
if (!l1d_flush_mitigation || !boot_cpu_has(X86_FEATURE_FLUSH_L1D))
return;
static_branch_enable(&switch_mm_cond_l1d_flush);
pr_info("Conditional flush on switch_mm() enabled\n");
}
static int __init l1d_flush_parse_cmdline(char *str)
{
if (!strcmp(str, "on"))
l1d_flush_mitigation = L1D_FLUSH_ON;
return 0;
}
early_param("l1d_flush", l1d_flush_parse_cmdline);
#undef pr_fmt
#define pr_fmt(fmt) "GDS: " fmt
enum gds_mitigations {
GDS_MITIGATION_OFF,
GDS_MITIGATION_UCODE_NEEDED,
GDS_MITIGATION_FORCE,
GDS_MITIGATION_FULL,
GDS_MITIGATION_FULL_LOCKED,
GDS_MITIGATION_HYPERVISOR,
};
static enum gds_mitigations gds_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_GDS) ? GDS_MITIGATION_FULL : GDS_MITIGATION_OFF;
static const char * const gds_strings[] = {
[GDS_MITIGATION_OFF] = "Vulnerable",
[GDS_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode",
[GDS_MITIGATION_FORCE] = "Mitigation: AVX disabled, no microcode",
[GDS_MITIGATION_FULL] = "Mitigation: Microcode",
[GDS_MITIGATION_FULL_LOCKED] = "Mitigation: Microcode (locked)",
[GDS_MITIGATION_HYPERVISOR] = "Unknown: Dependent on hypervisor status",
};
bool gds_ucode_mitigated(void)
{
return (gds_mitigation == GDS_MITIGATION_FULL ||
gds_mitigation == GDS_MITIGATION_FULL_LOCKED);
}
EXPORT_SYMBOL_GPL(gds_ucode_mitigated);
void update_gds_msr(void)
{
u64 mcu_ctrl_after;
u64 mcu_ctrl;
switch (gds_mitigation) {
case GDS_MITIGATION_OFF:
rdmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl);
mcu_ctrl |= GDS_MITG_DIS;
break;
case GDS_MITIGATION_FULL_LOCKED:
/*
* The LOCKED state comes from the boot CPU. APs might not have
* the same state. Make sure the mitigation is enabled on all
* CPUs.
*/
case GDS_MITIGATION_FULL:
rdmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl);
mcu_ctrl &= ~GDS_MITG_DIS;
break;
case GDS_MITIGATION_FORCE:
case GDS_MITIGATION_UCODE_NEEDED:
case GDS_MITIGATION_HYPERVISOR:
return;
}
wrmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl);
/*
* Check to make sure that the WRMSR value was not ignored. Writes to
* GDS_MITG_DIS will be ignored if this processor is locked but the boot
* processor was not.
*/
rdmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl_after);
WARN_ON_ONCE(mcu_ctrl != mcu_ctrl_after);
}
static void __init gds_select_mitigation(void)
{
u64 mcu_ctrl;
if (!boot_cpu_has_bug(X86_BUG_GDS))
return;
if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
gds_mitigation = GDS_MITIGATION_HYPERVISOR;
goto out;
}
if (cpu_mitigations_off())
gds_mitigation = GDS_MITIGATION_OFF;
/* Will verify below that mitigation _can_ be disabled */
/* No microcode */
if (!(x86_arch_cap_msr & ARCH_CAP_GDS_CTRL)) {
if (gds_mitigation == GDS_MITIGATION_FORCE) {
/*
* This only needs to be done on the boot CPU so do it
* here rather than in update_gds_msr()
*/
setup_clear_cpu_cap(X86_FEATURE_AVX);
pr_warn("Microcode update needed! Disabling AVX as mitigation.\n");
} else {
gds_mitigation = GDS_MITIGATION_UCODE_NEEDED;
}
goto out;
}
/* Microcode has mitigation, use it */
if (gds_mitigation == GDS_MITIGATION_FORCE)
gds_mitigation = GDS_MITIGATION_FULL;
rdmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl);
if (mcu_ctrl & GDS_MITG_LOCKED) {
if (gds_mitigation == GDS_MITIGATION_OFF)
pr_warn("Mitigation locked. Disable failed.\n");
/*
* The mitigation is selected from the boot CPU. All other CPUs
* _should_ have the same state. If the boot CPU isn't locked
* but others are then update_gds_msr() will WARN() of the state
* mismatch. If the boot CPU is locked update_gds_msr() will
* ensure the other CPUs have the mitigation enabled.
*/
gds_mitigation = GDS_MITIGATION_FULL_LOCKED;
}
update_gds_msr();
out:
pr_info("%s\n", gds_strings[gds_mitigation]);
}
static int __init gds_parse_cmdline(char *str)
{
if (!str)
return -EINVAL;
if (!boot_cpu_has_bug(X86_BUG_GDS))
return 0;
if (!strcmp(str, "off"))
gds_mitigation = GDS_MITIGATION_OFF;
else if (!strcmp(str, "force"))
gds_mitigation = GDS_MITIGATION_FORCE;
return 0;
}
early_param("gather_data_sampling", gds_parse_cmdline);
#undef pr_fmt
#define pr_fmt(fmt) "Spectre V1 : " fmt
enum spectre_v1_mitigation {
SPECTRE_V1_MITIGATION_NONE,
SPECTRE_V1_MITIGATION_AUTO,
};
static enum spectre_v1_mitigation spectre_v1_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_SPECTRE_V1) ?
SPECTRE_V1_MITIGATION_AUTO : SPECTRE_V1_MITIGATION_NONE;
static const char * const spectre_v1_strings[] = {
[SPECTRE_V1_MITIGATION_NONE] = "Vulnerable: __user pointer sanitization and usercopy barriers only; no swapgs barriers",
[SPECTRE_V1_MITIGATION_AUTO] = "Mitigation: usercopy/swapgs barriers and __user pointer sanitization",
};
/*
* Does SMAP provide full mitigation against speculative kernel access to
* userspace?
*/
static bool smap_works_speculatively(void)
{
if (!boot_cpu_has(X86_FEATURE_SMAP))
return false;
/*
* On CPUs which are vulnerable to Meltdown, SMAP does not
* prevent speculative access to user data in the L1 cache.
* Consider SMAP to be non-functional as a mitigation on these
* CPUs.
*/
if (boot_cpu_has(X86_BUG_CPU_MELTDOWN))
return false;
return true;
}
static void __init spectre_v1_select_mitigation(void)
{
if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V1) || cpu_mitigations_off()) {
spectre_v1_mitigation = SPECTRE_V1_MITIGATION_NONE;
return;
}
if (spectre_v1_mitigation == SPECTRE_V1_MITIGATION_AUTO) {
/*
* With Spectre v1, a user can speculatively control either
* path of a conditional swapgs with a user-controlled GS
* value. The mitigation is to add lfences to both code paths.
*
* If FSGSBASE is enabled, the user can put a kernel address in
* GS, in which case SMAP provides no protection.
*
* If FSGSBASE is disabled, the user can only put a user space
* address in GS. That makes an attack harder, but still
* possible if there's no SMAP protection.
*/
if (boot_cpu_has(X86_FEATURE_FSGSBASE) ||
!smap_works_speculatively()) {
/*
* Mitigation can be provided from SWAPGS itself or
* PTI as the CR3 write in the Meltdown mitigation
* is serializing.
*
* If neither is there, mitigate with an LFENCE to
* stop speculation through swapgs.
*/
if (boot_cpu_has_bug(X86_BUG_SWAPGS) &&
!boot_cpu_has(X86_FEATURE_PTI))
setup_force_cpu_cap(X86_FEATURE_FENCE_SWAPGS_USER);
/*
* Enable lfences in the kernel entry (non-swapgs)
* paths, to prevent user entry from speculatively
* skipping swapgs.
*/
setup_force_cpu_cap(X86_FEATURE_FENCE_SWAPGS_KERNEL);
}
}
pr_info("%s\n", spectre_v1_strings[spectre_v1_mitigation]);
}
static int __init nospectre_v1_cmdline(char *str)
{
spectre_v1_mitigation = SPECTRE_V1_MITIGATION_NONE;
return 0;
}
early_param("nospectre_v1", nospectre_v1_cmdline);
enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init = SPECTRE_V2_NONE;
#undef pr_fmt
#define pr_fmt(fmt) "RETBleed: " fmt
enum retbleed_mitigation {
RETBLEED_MITIGATION_NONE,
RETBLEED_MITIGATION_UNRET,
RETBLEED_MITIGATION_IBPB,
RETBLEED_MITIGATION_IBRS,
RETBLEED_MITIGATION_EIBRS,
RETBLEED_MITIGATION_STUFF,
};
enum retbleed_mitigation_cmd {
RETBLEED_CMD_OFF,
RETBLEED_CMD_AUTO,
RETBLEED_CMD_UNRET,
RETBLEED_CMD_IBPB,
RETBLEED_CMD_STUFF,
};
static const char * const retbleed_strings[] = {
[RETBLEED_MITIGATION_NONE] = "Vulnerable",
[RETBLEED_MITIGATION_UNRET] = "Mitigation: untrained return thunk",
[RETBLEED_MITIGATION_IBPB] = "Mitigation: IBPB",
[RETBLEED_MITIGATION_IBRS] = "Mitigation: IBRS",
[RETBLEED_MITIGATION_EIBRS] = "Mitigation: Enhanced IBRS",
[RETBLEED_MITIGATION_STUFF] = "Mitigation: Stuffing",
};
static enum retbleed_mitigation retbleed_mitigation __ro_after_init =
RETBLEED_MITIGATION_NONE;
static enum retbleed_mitigation_cmd retbleed_cmd __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_RETBLEED) ? RETBLEED_CMD_AUTO : RETBLEED_CMD_OFF;
static int __ro_after_init retbleed_nosmt = false;
static int __init retbleed_parse_cmdline(char *str)
{
if (!str)
return -EINVAL;
while (str) {
char *next = strchr(str, ',');
if (next) {
*next = 0;
next++;
}
if (!strcmp(str, "off")) {
retbleed_cmd = RETBLEED_CMD_OFF;
} else if (!strcmp(str, "auto")) {
retbleed_cmd = RETBLEED_CMD_AUTO;
} else if (!strcmp(str, "unret")) {
retbleed_cmd = RETBLEED_CMD_UNRET;
} else if (!strcmp(str, "ibpb")) {
retbleed_cmd = RETBLEED_CMD_IBPB;
} else if (!strcmp(str, "stuff")) {
retbleed_cmd = RETBLEED_CMD_STUFF;
} else if (!strcmp(str, "nosmt")) {
retbleed_nosmt = true;
} else if (!strcmp(str, "force")) {
setup_force_cpu_bug(X86_BUG_RETBLEED);
} else {
pr_err("Ignoring unknown retbleed option (%s).", str);
}
str = next;
}
return 0;
}
early_param("retbleed", retbleed_parse_cmdline);
#define RETBLEED_UNTRAIN_MSG "WARNING: BTB untrained return thunk mitigation is only effective on AMD/Hygon!\n"
#define RETBLEED_INTEL_MSG "WARNING: Spectre v2 mitigation leaves CPU vulnerable to RETBleed attacks, data leaks possible!\n"
static void __init retbleed_select_mitigation(void)
{
bool mitigate_smt = false;
if (!boot_cpu_has_bug(X86_BUG_RETBLEED) || cpu_mitigations_off())
return;
switch (retbleed_cmd) {
case RETBLEED_CMD_OFF:
return;
case RETBLEED_CMD_UNRET:
if (IS_ENABLED(CONFIG_MITIGATION_UNRET_ENTRY)) {
retbleed_mitigation = RETBLEED_MITIGATION_UNRET;
} else {
pr_err("WARNING: kernel not compiled with MITIGATION_UNRET_ENTRY.\n");
goto do_cmd_auto;
}
break;
case RETBLEED_CMD_IBPB:
if (!boot_cpu_has(X86_FEATURE_IBPB)) {
pr_err("WARNING: CPU does not support IBPB.\n");
goto do_cmd_auto;
} else if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY)) {
retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
} else {
pr_err("WARNING: kernel not compiled with MITIGATION_IBPB_ENTRY.\n");
goto do_cmd_auto;
}
break;
case RETBLEED_CMD_STUFF:
if (IS_ENABLED(CONFIG_MITIGATION_CALL_DEPTH_TRACKING) &&
spectre_v2_enabled == SPECTRE_V2_RETPOLINE) {
retbleed_mitigation = RETBLEED_MITIGATION_STUFF;
} else {
if (IS_ENABLED(CONFIG_MITIGATION_CALL_DEPTH_TRACKING))
pr_err("WARNING: retbleed=stuff depends on spectre_v2=retpoline\n");
else
pr_err("WARNING: kernel not compiled with MITIGATION_CALL_DEPTH_TRACKING.\n");
goto do_cmd_auto;
}
break;
do_cmd_auto:
case RETBLEED_CMD_AUTO:
if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
if (IS_ENABLED(CONFIG_MITIGATION_UNRET_ENTRY))
retbleed_mitigation = RETBLEED_MITIGATION_UNRET;
else if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY) &&
boot_cpu_has(X86_FEATURE_IBPB))
retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
}
/*
* The Intel mitigation (IBRS or eIBRS) was already selected in
* spectre_v2_select_mitigation(). 'retbleed_mitigation' will
* be set accordingly below.
*/
break;
}
switch (retbleed_mitigation) {
case RETBLEED_MITIGATION_UNRET:
setup_force_cpu_cap(X86_FEATURE_RETHUNK);
setup_force_cpu_cap(X86_FEATURE_UNRET);
x86_return_thunk = retbleed_return_thunk;
if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
pr_err(RETBLEED_UNTRAIN_MSG);
mitigate_smt = true;
break;
case RETBLEED_MITIGATION_IBPB:
setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
/*
* IBPB on entry already obviates the need for
* software-based untraining so clear those in case some
* other mitigation like SRSO has selected them.
*/
setup_clear_cpu_cap(X86_FEATURE_UNRET);
setup_clear_cpu_cap(X86_FEATURE_RETHUNK);
setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
mitigate_smt = true;
/*
* There is no need for RSB filling: entry_ibpb() ensures
* all predictions, including the RSB, are invalidated,
* regardless of IBPB implementation.
*/
setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT);
break;
case RETBLEED_MITIGATION_STUFF:
setup_force_cpu_cap(X86_FEATURE_RETHUNK);
setup_force_cpu_cap(X86_FEATURE_CALL_DEPTH);
x86_return_thunk = call_depth_return_thunk;
break;
default:
break;
}
if (mitigate_smt && !boot_cpu_has(X86_FEATURE_STIBP) &&
(retbleed_nosmt || cpu_mitigations_auto_nosmt()))
cpu_smt_disable(false);
/*
* Let IBRS trump all on Intel without affecting the effects of the
* retbleed= cmdline option except for call depth based stuffing
*/
if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
switch (spectre_v2_enabled) {
case SPECTRE_V2_IBRS:
retbleed_mitigation = RETBLEED_MITIGATION_IBRS;
break;
case SPECTRE_V2_EIBRS:
case SPECTRE_V2_EIBRS_RETPOLINE:
case SPECTRE_V2_EIBRS_LFENCE:
retbleed_mitigation = RETBLEED_MITIGATION_EIBRS;
break;
default:
if (retbleed_mitigation != RETBLEED_MITIGATION_STUFF)
pr_err(RETBLEED_INTEL_MSG);
}
}
pr_info("%s\n", retbleed_strings[retbleed_mitigation]);
}
#undef pr_fmt
#define pr_fmt(fmt) "Spectre V2 : " fmt
static enum spectre_v2_user_mitigation spectre_v2_user_stibp __ro_after_init =
SPECTRE_V2_USER_NONE;
static enum spectre_v2_user_mitigation spectre_v2_user_ibpb __ro_after_init =
SPECTRE_V2_USER_NONE;
#ifdef CONFIG_MITIGATION_RETPOLINE
static bool spectre_v2_bad_module;
bool retpoline_module_ok(bool has_retpoline)
{
if (spectre_v2_enabled == SPECTRE_V2_NONE || has_retpoline)
return true;
pr_err("System may be vulnerable to spectre v2\n");
spectre_v2_bad_module = true;
return false;
}
static inline const char *spectre_v2_module_string(void)
{
return spectre_v2_bad_module ? " - vulnerable module loaded" : "";
}
#else
static inline const char *spectre_v2_module_string(void) { return ""; }
#endif
#define SPECTRE_V2_LFENCE_MSG "WARNING: LFENCE mitigation is not recommended for this CPU, data leaks possible!\n"
#define SPECTRE_V2_EIBRS_EBPF_MSG "WARNING: Unprivileged eBPF is enabled with eIBRS on, data leaks possible via Spectre v2 BHB attacks!\n"
#define SPECTRE_V2_EIBRS_LFENCE_EBPF_SMT_MSG "WARNING: Unprivileged eBPF is enabled with eIBRS+LFENCE mitigation and SMT, data leaks possible via Spectre v2 BHB attacks!\n"
#define SPECTRE_V2_IBRS_PERF_MSG "WARNING: IBRS mitigation selected on Enhanced IBRS CPU, this may cause unnecessary performance loss\n"
#ifdef CONFIG_BPF_SYSCALL
void unpriv_ebpf_notify(int new_state)
{
if (new_state)
return;
/* Unprivileged eBPF is enabled */
switch (spectre_v2_enabled) {
case SPECTRE_V2_EIBRS:
pr_err(SPECTRE_V2_EIBRS_EBPF_MSG);
break;
case SPECTRE_V2_EIBRS_LFENCE:
if (sched_smt_active())
pr_err(SPECTRE_V2_EIBRS_LFENCE_EBPF_SMT_MSG);
break;
default:
break;
}
}
#endif
static inline bool match_option(const char *arg, int arglen, const char *opt)
{
int len = strlen(opt);
return len == arglen && !strncmp(arg, opt, len);
}
/* The kernel command line selection for spectre v2 */
enum spectre_v2_mitigation_cmd {
SPECTRE_V2_CMD_NONE,
SPECTRE_V2_CMD_AUTO,
SPECTRE_V2_CMD_FORCE,
SPECTRE_V2_CMD_RETPOLINE,
SPECTRE_V2_CMD_RETPOLINE_GENERIC,
SPECTRE_V2_CMD_RETPOLINE_LFENCE,
SPECTRE_V2_CMD_EIBRS,
SPECTRE_V2_CMD_EIBRS_RETPOLINE,
SPECTRE_V2_CMD_EIBRS_LFENCE,
SPECTRE_V2_CMD_IBRS,
};
enum spectre_v2_user_cmd {
SPECTRE_V2_USER_CMD_NONE,
SPECTRE_V2_USER_CMD_AUTO,
SPECTRE_V2_USER_CMD_FORCE,
SPECTRE_V2_USER_CMD_PRCTL,
SPECTRE_V2_USER_CMD_PRCTL_IBPB,
SPECTRE_V2_USER_CMD_SECCOMP,
SPECTRE_V2_USER_CMD_SECCOMP_IBPB,
};
static const char * const spectre_v2_user_strings[] = {
[SPECTRE_V2_USER_NONE] = "User space: Vulnerable",
[SPECTRE_V2_USER_STRICT] = "User space: Mitigation: STIBP protection",
[SPECTRE_V2_USER_STRICT_PREFERRED] = "User space: Mitigation: STIBP always-on protection",
[SPECTRE_V2_USER_PRCTL] = "User space: Mitigation: STIBP via prctl",
[SPECTRE_V2_USER_SECCOMP] = "User space: Mitigation: STIBP via seccomp and prctl",
};
static const struct {
const char *option;
enum spectre_v2_user_cmd cmd;
bool secure;
} v2_user_options[] __initconst = {
{ "auto", SPECTRE_V2_USER_CMD_AUTO, false },
{ "off", SPECTRE_V2_USER_CMD_NONE, false },
{ "on", SPECTRE_V2_USER_CMD_FORCE, true },
{ "prctl", SPECTRE_V2_USER_CMD_PRCTL, false },
{ "prctl,ibpb", SPECTRE_V2_USER_CMD_PRCTL_IBPB, false },
{ "seccomp", SPECTRE_V2_USER_CMD_SECCOMP, false },
{ "seccomp,ibpb", SPECTRE_V2_USER_CMD_SECCOMP_IBPB, false },
};
static void __init spec_v2_user_print_cond(const char *reason, bool secure)
{
if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2) != secure)
pr_info("spectre_v2_user=%s forced on command line.\n", reason);
}
static __ro_after_init enum spectre_v2_mitigation_cmd spectre_v2_cmd;
static enum spectre_v2_user_cmd __init
spectre_v2_parse_user_cmdline(void)
{
char arg[20];
int ret, i;
switch (spectre_v2_cmd) {
case SPECTRE_V2_CMD_NONE:
return SPECTRE_V2_USER_CMD_NONE;
case SPECTRE_V2_CMD_FORCE:
return SPECTRE_V2_USER_CMD_FORCE;
default:
break;
}
ret = cmdline_find_option(boot_command_line, "spectre_v2_user",
arg, sizeof(arg));
if (ret < 0)
return SPECTRE_V2_USER_CMD_AUTO;
for (i = 0; i < ARRAY_SIZE(v2_user_options); i++) {
if (match_option(arg, ret, v2_user_options[i].option)) {
spec_v2_user_print_cond(v2_user_options[i].option,
v2_user_options[i].secure);
return v2_user_options[i].cmd;
}
}
pr_err("Unknown user space protection option (%s). Switching to AUTO select\n", arg);
return SPECTRE_V2_USER_CMD_AUTO;
}
static inline bool spectre_v2_in_ibrs_mode(enum spectre_v2_mitigation mode)
{
return spectre_v2_in_eibrs_mode(mode) || mode == SPECTRE_V2_IBRS;
}
static void __init
spectre_v2_user_select_mitigation(void)
{
enum spectre_v2_user_mitigation mode = SPECTRE_V2_USER_NONE;
bool smt_possible = IS_ENABLED(CONFIG_SMP);
enum spectre_v2_user_cmd cmd;
if (!boot_cpu_has(X86_FEATURE_IBPB) && !boot_cpu_has(X86_FEATURE_STIBP))
return;
if (cpu_smt_control == CPU_SMT_FORCE_DISABLED ||
cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
smt_possible = false;
cmd = spectre_v2_parse_user_cmdline();
switch (cmd) {
case SPECTRE_V2_USER_CMD_NONE:
goto set_mode;
case SPECTRE_V2_USER_CMD_FORCE:
mode = SPECTRE_V2_USER_STRICT;
break;
case SPECTRE_V2_USER_CMD_AUTO:
case SPECTRE_V2_USER_CMD_PRCTL:
case SPECTRE_V2_USER_CMD_PRCTL_IBPB:
mode = SPECTRE_V2_USER_PRCTL;
break;
case SPECTRE_V2_USER_CMD_SECCOMP:
case SPECTRE_V2_USER_CMD_SECCOMP_IBPB:
if (IS_ENABLED(CONFIG_SECCOMP))
mode = SPECTRE_V2_USER_SECCOMP;
else
mode = SPECTRE_V2_USER_PRCTL;
break;
}
/* Initialize Indirect Branch Prediction Barrier */
if (boot_cpu_has(X86_FEATURE_IBPB)) {
setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
spectre_v2_user_ibpb = mode;
switch (cmd) {
case SPECTRE_V2_USER_CMD_NONE:
break;
case SPECTRE_V2_USER_CMD_FORCE:
case SPECTRE_V2_USER_CMD_PRCTL_IBPB:
case SPECTRE_V2_USER_CMD_SECCOMP_IBPB:
static_branch_enable(&switch_mm_always_ibpb);
spectre_v2_user_ibpb = SPECTRE_V2_USER_STRICT;
break;
case SPECTRE_V2_USER_CMD_PRCTL:
case SPECTRE_V2_USER_CMD_AUTO:
case SPECTRE_V2_USER_CMD_SECCOMP:
static_branch_enable(&switch_mm_cond_ibpb);
break;
}
pr_info("mitigation: Enabling %s Indirect Branch Prediction Barrier\n",
static_key_enabled(&switch_mm_always_ibpb) ?
"always-on" : "conditional");
}
/*
* If no STIBP, Intel enhanced IBRS is enabled, or SMT impossible, STIBP
* is not required.
*
* Intel's Enhanced IBRS also protects against cross-thread branch target
* injection in user-mode as the IBRS bit remains always set which
* implicitly enables cross-thread protections. However, in legacy IBRS
* mode, the IBRS bit is set only on kernel entry and cleared on return
* to userspace. AMD Automatic IBRS also does not protect userspace.
* These modes therefore disable the implicit cross-thread protection,
* so allow for STIBP to be selected in those cases.
*/
if (!boot_cpu_has(X86_FEATURE_STIBP) ||
!smt_possible ||
(spectre_v2_in_eibrs_mode(spectre_v2_enabled) &&
!boot_cpu_has(X86_FEATURE_AUTOIBRS)))
return;
/*
* At this point, an STIBP mode other than "off" has been set.
* If STIBP support is not being forced, check if STIBP always-on
* is preferred.
*/
if (mode != SPECTRE_V2_USER_STRICT &&
boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
mode = SPECTRE_V2_USER_STRICT_PREFERRED;
if (retbleed_mitigation == RETBLEED_MITIGATION_UNRET ||
retbleed_mitigation == RETBLEED_MITIGATION_IBPB) {
if (mode != SPECTRE_V2_USER_STRICT &&
mode != SPECTRE_V2_USER_STRICT_PREFERRED)
pr_info("Selecting STIBP always-on mode to complement retbleed mitigation\n");
mode = SPECTRE_V2_USER_STRICT_PREFERRED;
}
spectre_v2_user_stibp = mode;
set_mode:
pr_info("%s\n", spectre_v2_user_strings[mode]);
}
static const char * const spectre_v2_strings[] = {
[SPECTRE_V2_NONE] = "Vulnerable",
[SPECTRE_V2_RETPOLINE] = "Mitigation: Retpolines",
[SPECTRE_V2_LFENCE] = "Mitigation: LFENCE",
[SPECTRE_V2_EIBRS] = "Mitigation: Enhanced / Automatic IBRS",
[SPECTRE_V2_EIBRS_LFENCE] = "Mitigation: Enhanced / Automatic IBRS + LFENCE",
[SPECTRE_V2_EIBRS_RETPOLINE] = "Mitigation: Enhanced / Automatic IBRS + Retpolines",
[SPECTRE_V2_IBRS] = "Mitigation: IBRS",
};
static const struct {
const char *option;
enum spectre_v2_mitigation_cmd cmd;
bool secure;
} mitigation_options[] __initconst = {
{ "off", SPECTRE_V2_CMD_NONE, false },
{ "on", SPECTRE_V2_CMD_FORCE, true },
{ "retpoline", SPECTRE_V2_CMD_RETPOLINE, false },
{ "retpoline,amd", SPECTRE_V2_CMD_RETPOLINE_LFENCE, false },
{ "retpoline,lfence", SPECTRE_V2_CMD_RETPOLINE_LFENCE, false },
{ "retpoline,generic", SPECTRE_V2_CMD_RETPOLINE_GENERIC, false },
{ "eibrs", SPECTRE_V2_CMD_EIBRS, false },
{ "eibrs,lfence", SPECTRE_V2_CMD_EIBRS_LFENCE, false },
{ "eibrs,retpoline", SPECTRE_V2_CMD_EIBRS_RETPOLINE, false },
{ "auto", SPECTRE_V2_CMD_AUTO, false },
{ "ibrs", SPECTRE_V2_CMD_IBRS, false },
};
static void __init spec_v2_print_cond(const char *reason, bool secure)
{
if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2) != secure)
pr_info("%s selected on command line.\n", reason);
}
static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
{
enum spectre_v2_mitigation_cmd cmd;
char arg[20];
int ret, i;
cmd = IS_ENABLED(CONFIG_MITIGATION_SPECTRE_V2) ? SPECTRE_V2_CMD_AUTO : SPECTRE_V2_CMD_NONE;
if (cmdline_find_option_bool(boot_command_line, "nospectre_v2") ||
cpu_mitigations_off())
return SPECTRE_V2_CMD_NONE;
ret = cmdline_find_option(boot_command_line, "spectre_v2", arg, sizeof(arg));
if (ret < 0)
return cmd;
for (i = 0; i < ARRAY_SIZE(mitigation_options); i++) {
if (!match_option(arg, ret, mitigation_options[i].option))
continue;
cmd = mitigation_options[i].cmd;
break;
}
if (i >= ARRAY_SIZE(mitigation_options)) {
pr_err("unknown option (%s). Switching to default mode\n", arg);
return cmd;
}
if ((cmd == SPECTRE_V2_CMD_RETPOLINE ||
cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE ||
cmd == SPECTRE_V2_CMD_RETPOLINE_GENERIC ||
cmd == SPECTRE_V2_CMD_EIBRS_LFENCE ||
cmd == SPECTRE_V2_CMD_EIBRS_RETPOLINE) &&
!IS_ENABLED(CONFIG_MITIGATION_RETPOLINE)) {
pr_err("%s selected but not compiled in. Switching to AUTO select\n",
mitigation_options[i].option);
return SPECTRE_V2_CMD_AUTO;
}
if ((cmd == SPECTRE_V2_CMD_EIBRS ||
cmd == SPECTRE_V2_CMD_EIBRS_LFENCE ||
cmd == SPECTRE_V2_CMD_EIBRS_RETPOLINE) &&
!boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) {
pr_err("%s selected but CPU doesn't have Enhanced or Automatic IBRS. Switching to AUTO select\n",
mitigation_options[i].option);
return SPECTRE_V2_CMD_AUTO;
}
if ((cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE ||
cmd == SPECTRE_V2_CMD_EIBRS_LFENCE) &&
!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
pr_err("%s selected, but CPU doesn't have a serializing LFENCE. Switching to AUTO select\n",
mitigation_options[i].option);
return SPECTRE_V2_CMD_AUTO;
}
if (cmd == SPECTRE_V2_CMD_IBRS && !IS_ENABLED(CONFIG_MITIGATION_IBRS_ENTRY)) {
pr_err("%s selected but not compiled in. Switching to AUTO select\n",
mitigation_options[i].option);
return SPECTRE_V2_CMD_AUTO;
}
if (cmd == SPECTRE_V2_CMD_IBRS && boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
pr_err("%s selected but not Intel CPU. Switching to AUTO select\n",
mitigation_options[i].option);
return SPECTRE_V2_CMD_AUTO;
}
if (cmd == SPECTRE_V2_CMD_IBRS && !boot_cpu_has(X86_FEATURE_IBRS)) {
pr_err("%s selected but CPU doesn't have IBRS. Switching to AUTO select\n",
mitigation_options[i].option);
return SPECTRE_V2_CMD_AUTO;
}
if (cmd == SPECTRE_V2_CMD_IBRS && cpu_feature_enabled(X86_FEATURE_XENPV)) {
pr_err("%s selected but running as XenPV guest. Switching to AUTO select\n",
mitigation_options[i].option);
return SPECTRE_V2_CMD_AUTO;
}
spec_v2_print_cond(mitigation_options[i].option,
mitigation_options[i].secure);
return cmd;
}
static enum spectre_v2_mitigation __init spectre_v2_select_retpoline(void)
{
if (!IS_ENABLED(CONFIG_MITIGATION_RETPOLINE)) {
pr_err("Kernel not compiled with retpoline; no mitigation available!");
return SPECTRE_V2_NONE;
}
return SPECTRE_V2_RETPOLINE;
}
static bool __ro_after_init rrsba_disabled;
/* Disable in-kernel use of non-RSB RET predictors */
static void __init spec_ctrl_disable_kernel_rrsba(void)
{
if (rrsba_disabled)
return;
if (!(x86_arch_cap_msr & ARCH_CAP_RRSBA)) {
rrsba_disabled = true;
return;
}
if (!boot_cpu_has(X86_FEATURE_RRSBA_CTRL))
return;
x86_spec_ctrl_base |= SPEC_CTRL_RRSBA_DIS_S;
update_spec_ctrl(x86_spec_ctrl_base);
rrsba_disabled = true;
}
static void __init spectre_v2_determine_rsb_fill_type_at_vmexit(enum spectre_v2_mitigation mode)
{
/*
* Similar to context switches, there are two types of RSB attacks
* after VM exit:
*
* 1) RSB underflow
*
* 2) Poisoned RSB entry
*
* When retpoline is enabled, both are mitigated by filling/clearing
* the RSB.
*
* When IBRS is enabled, while #1 would be mitigated by the IBRS branch
* prediction isolation protections, RSB still needs to be cleared
* because of #2. Note that SMEP provides no protection here, unlike
* user-space-poisoned RSB entries.
*
* eIBRS should protect against RSB poisoning, but if the EIBRS_PBRSB
* bug is present then a LITE version of RSB protection is required,
* just a single call needs to retire before a RET is executed.
*/
switch (mode) {
case SPECTRE_V2_NONE:
return;
case SPECTRE_V2_EIBRS_LFENCE:
case SPECTRE_V2_EIBRS:
if (boot_cpu_has_bug(X86_BUG_EIBRS_PBRSB)) {
setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT_LITE);
pr_info("Spectre v2 / PBRSB-eIBRS: Retire a single CALL on VMEXIT\n");
}
return;
case SPECTRE_V2_EIBRS_RETPOLINE:
case SPECTRE_V2_RETPOLINE:
case SPECTRE_V2_LFENCE:
case SPECTRE_V2_IBRS:
setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT);
pr_info("Spectre v2 / SpectreRSB : Filling RSB on VMEXIT\n");
return;
}
pr_warn_once("Unknown Spectre v2 mode, disabling RSB mitigation at VM exit");
dump_stack();
}
/*
* Set BHI_DIS_S to prevent indirect branches in kernel to be influenced by
* branch history in userspace. Not needed if BHI_NO is set.
*/
static bool __init spec_ctrl_bhi_dis(void)
{
if (!boot_cpu_has(X86_FEATURE_BHI_CTRL))
return false;
x86_spec_ctrl_base |= SPEC_CTRL_BHI_DIS_S;
update_spec_ctrl(x86_spec_ctrl_base);
setup_force_cpu_cap(X86_FEATURE_CLEAR_BHB_HW);
return true;
}
enum bhi_mitigations {
BHI_MITIGATION_OFF,
BHI_MITIGATION_ON,
BHI_MITIGATION_VMEXIT_ONLY,
};
static enum bhi_mitigations bhi_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_SPECTRE_BHI) ? BHI_MITIGATION_ON : BHI_MITIGATION_OFF;
static int __init spectre_bhi_parse_cmdline(char *str)
{
if (!str)
return -EINVAL;
if (!strcmp(str, "off"))
bhi_mitigation = BHI_MITIGATION_OFF;
else if (!strcmp(str, "on"))
bhi_mitigation = BHI_MITIGATION_ON;
else if (!strcmp(str, "vmexit"))
bhi_mitigation = BHI_MITIGATION_VMEXIT_ONLY;
else
pr_err("Ignoring unknown spectre_bhi option (%s)", str);
return 0;
}
early_param("spectre_bhi", spectre_bhi_parse_cmdline);
static void __init bhi_select_mitigation(void)
{
if (bhi_mitigation == BHI_MITIGATION_OFF)
return;
/* Retpoline mitigates against BHI unless the CPU has RRSBA behavior */
if (boot_cpu_has(X86_FEATURE_RETPOLINE) &&
!boot_cpu_has(X86_FEATURE_RETPOLINE_LFENCE)) {
spec_ctrl_disable_kernel_rrsba();
if (rrsba_disabled)
return;
}
/* Mitigate in hardware if supported */
if (spec_ctrl_bhi_dis())
return;
if (!IS_ENABLED(CONFIG_X86_64))
return;
if (bhi_mitigation == BHI_MITIGATION_VMEXIT_ONLY) {
pr_info("Spectre BHI mitigation: SW BHB clearing on VM exit only\n");
setup_force_cpu_cap(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT);
return;
}
pr_info("Spectre BHI mitigation: SW BHB clearing on syscall and VM exit\n");
setup_force_cpu_cap(X86_FEATURE_CLEAR_BHB_LOOP);
setup_force_cpu_cap(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT);
}
static void __init spectre_v2_select_mitigation(void)
{
enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
enum spectre_v2_mitigation mode = SPECTRE_V2_NONE;
/*
* If the CPU is not affected and the command line mode is NONE or AUTO
* then nothing to do.
*/
if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2) &&
(cmd == SPECTRE_V2_CMD_NONE || cmd == SPECTRE_V2_CMD_AUTO))
return;
switch (cmd) {
case SPECTRE_V2_CMD_NONE:
return;
case SPECTRE_V2_CMD_FORCE:
case SPECTRE_V2_CMD_AUTO:
if (boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) {
mode = SPECTRE_V2_EIBRS;
break;
}
if (IS_ENABLED(CONFIG_MITIGATION_IBRS_ENTRY) &&
boot_cpu_has_bug(X86_BUG_RETBLEED) &&
retbleed_cmd != RETBLEED_CMD_OFF &&
retbleed_cmd != RETBLEED_CMD_STUFF &&
boot_cpu_has(X86_FEATURE_IBRS) &&
boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
mode = SPECTRE_V2_IBRS;
break;
}
mode = spectre_v2_select_retpoline();
break;
case SPECTRE_V2_CMD_RETPOLINE_LFENCE:
pr_err(SPECTRE_V2_LFENCE_MSG);
mode = SPECTRE_V2_LFENCE;
break;
case SPECTRE_V2_CMD_RETPOLINE_GENERIC:
mode = SPECTRE_V2_RETPOLINE;
break;
case SPECTRE_V2_CMD_RETPOLINE:
mode = spectre_v2_select_retpoline();
break;
case SPECTRE_V2_CMD_IBRS:
mode = SPECTRE_V2_IBRS;
break;
case SPECTRE_V2_CMD_EIBRS:
mode = SPECTRE_V2_EIBRS;
break;
case SPECTRE_V2_CMD_EIBRS_LFENCE:
mode = SPECTRE_V2_EIBRS_LFENCE;
break;
case SPECTRE_V2_CMD_EIBRS_RETPOLINE:
mode = SPECTRE_V2_EIBRS_RETPOLINE;
break;
}
if (mode == SPECTRE_V2_EIBRS && unprivileged_ebpf_enabled())
pr_err(SPECTRE_V2_EIBRS_EBPF_MSG);
if (spectre_v2_in_ibrs_mode(mode)) {
if (boot_cpu_has(X86_FEATURE_AUTOIBRS)) {
msr_set_bit(MSR_EFER, _EFER_AUTOIBRS);
} else {
x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
update_spec_ctrl(x86_spec_ctrl_base);
}
}
switch (mode) {
case SPECTRE_V2_NONE:
case SPECTRE_V2_EIBRS:
break;
case SPECTRE_V2_IBRS:
setup_force_cpu_cap(X86_FEATURE_KERNEL_IBRS);
if (boot_cpu_has(X86_FEATURE_IBRS_ENHANCED))
pr_warn(SPECTRE_V2_IBRS_PERF_MSG);
break;
case SPECTRE_V2_LFENCE:
case SPECTRE_V2_EIBRS_LFENCE:
setup_force_cpu_cap(X86_FEATURE_RETPOLINE_LFENCE);
fallthrough;
case SPECTRE_V2_RETPOLINE:
case SPECTRE_V2_EIBRS_RETPOLINE:
setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
break;
}
/*
* Disable alternate RSB predictions in kernel when indirect CALLs and
* JMPs gets protection against BHI and Intramode-BTI, but RET
* prediction from a non-RSB predictor is still a risk.
*/
if (mode == SPECTRE_V2_EIBRS_LFENCE ||
mode == SPECTRE_V2_EIBRS_RETPOLINE ||
mode == SPECTRE_V2_RETPOLINE)
spec_ctrl_disable_kernel_rrsba();
if (boot_cpu_has(X86_BUG_BHI))
bhi_select_mitigation();
spectre_v2_enabled = mode;
pr_info("%s\n", spectre_v2_strings[mode]);
/*
* If Spectre v2 protection has been enabled, fill the RSB during a
* context switch. In general there are two types of RSB attacks
* across context switches, for which the CALLs/RETs may be unbalanced.
*
* 1) RSB underflow
*
* Some Intel parts have "bottomless RSB". When the RSB is empty,
* speculated return targets may come from the branch predictor,
* which could have a user-poisoned BTB or BHB entry.
*
* AMD has it even worse: *all* returns are speculated from the BTB,
* regardless of the state of the RSB.
*
* When IBRS or eIBRS is enabled, the "user -> kernel" attack
* scenario is mitigated by the IBRS branch prediction isolation
* properties, so the RSB buffer filling wouldn't be necessary to
* protect against this type of attack.
*
* The "user -> user" attack scenario is mitigated by RSB filling.
*
* 2) Poisoned RSB entry
*
* If the 'next' in-kernel return stack is shorter than 'prev',
* 'next' could be tricked into speculating with a user-poisoned RSB
* entry.
*
* The "user -> kernel" attack scenario is mitigated by SMEP and
* eIBRS.
*
* The "user -> user" scenario, also known as SpectreBHB, requires
* RSB clearing.
*
* So to mitigate all cases, unconditionally fill RSB on context
* switches.
*
* FIXME: Is this pointless for retbleed-affected AMD?
*/
setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
pr_info("Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch\n");
spectre_v2_determine_rsb_fill_type_at_vmexit(mode);
/*
* Retpoline protects the kernel, but doesn't protect firmware. IBRS
* and Enhanced IBRS protect firmware too, so enable IBRS around
* firmware calls only when IBRS / Enhanced / Automatic IBRS aren't
* otherwise enabled.
*
* Use "mode" to check Enhanced IBRS instead of boot_cpu_has(), because
* the user might select retpoline on the kernel command line and if
* the CPU supports Enhanced IBRS, kernel might un-intentionally not
* enable IBRS around firmware calls.
*/
if (boot_cpu_has_bug(X86_BUG_RETBLEED) &&
boot_cpu_has(X86_FEATURE_IBPB) &&
(boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)) {
if (retbleed_cmd != RETBLEED_CMD_IBPB) {
setup_force_cpu_cap(X86_FEATURE_USE_IBPB_FW);
pr_info("Enabling Speculation Barrier for firmware calls\n");
}
} else if (boot_cpu_has(X86_FEATURE_IBRS) && !spectre_v2_in_ibrs_mode(mode)) {
setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);
pr_info("Enabling Restricted Speculation for firmware calls\n");
}
/* Set up IBPB and STIBP depending on the general spectre V2 command */
spectre_v2_cmd = cmd;
}
static void update_stibp_msr(void * __unused)
{
u64 val = spec_ctrl_current() | (x86_spec_ctrl_base & SPEC_CTRL_STIBP);
update_spec_ctrl(val);
}
/* Update x86_spec_ctrl_base in case SMT state changed. */
static void update_stibp_strict(void)
{
u64 mask = x86_spec_ctrl_base & ~SPEC_CTRL_STIBP;
if (sched_smt_active())
mask |= SPEC_CTRL_STIBP;
if (mask == x86_spec_ctrl_base)
return;
pr_info("Update user space SMT mitigation: STIBP %s\n",
mask & SPEC_CTRL_STIBP ? "always-on" : "off");
x86_spec_ctrl_base = mask;
on_each_cpu(update_stibp_msr, NULL, 1);
}
/* Update the static key controlling the evaluation of TIF_SPEC_IB */
static void update_indir_branch_cond(void)
{
if (sched_smt_active())
static_branch_enable(&switch_to_cond_stibp);
else
static_branch_disable(&switch_to_cond_stibp);
}
#undef pr_fmt
#define pr_fmt(fmt) fmt
/* Update the static key controlling the MDS CPU buffer clear in idle */
static void update_mds_branch_idle(void)
{
/*
* Enable the idle clearing if SMT is active on CPUs which are
* affected only by MSBDS and not any other MDS variant.
*
* The other variants cannot be mitigated when SMT is enabled, so
* clearing the buffers on idle just to prevent the Store Buffer
* repartitioning leak would be a window dressing exercise.
*/
if (!boot_cpu_has_bug(X86_BUG_MSBDS_ONLY))
return;
if (sched_smt_active()) {
static_branch_enable(&mds_idle_clear);
} else if (mmio_mitigation == MMIO_MITIGATION_OFF ||
(x86_arch_cap_msr & ARCH_CAP_FBSDP_NO)) {
static_branch_disable(&mds_idle_clear);
}
}
#define MDS_MSG_SMT "MDS CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html for more details.\n"
#define TAA_MSG_SMT "TAA CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/tsx_async_abort.html for more details.\n"
#define MMIO_MSG_SMT "MMIO Stale Data CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/processor_mmio_stale_data.html for more details.\n"
void cpu_bugs_smt_update(void)
{
mutex_lock(&spec_ctrl_mutex);
if (sched_smt_active() && unprivileged_ebpf_enabled() &&
spectre_v2_enabled == SPECTRE_V2_EIBRS_LFENCE)
pr_warn_once(SPECTRE_V2_EIBRS_LFENCE_EBPF_SMT_MSG);
switch (spectre_v2_user_stibp) {
case SPECTRE_V2_USER_NONE:
break;
case SPECTRE_V2_USER_STRICT:
case SPECTRE_V2_USER_STRICT_PREFERRED:
update_stibp_strict();
break;
case SPECTRE_V2_USER_PRCTL:
case SPECTRE_V2_USER_SECCOMP:
update_indir_branch_cond();
break;
}
switch (mds_mitigation) {
case MDS_MITIGATION_FULL:
case MDS_MITIGATION_VMWERV:
if (sched_smt_active() && !boot_cpu_has(X86_BUG_MSBDS_ONLY))
pr_warn_once(MDS_MSG_SMT);
update_mds_branch_idle();
break;
case MDS_MITIGATION_OFF:
break;
}
switch (taa_mitigation) {
case TAA_MITIGATION_VERW:
case TAA_MITIGATION_UCODE_NEEDED:
if (sched_smt_active())
pr_warn_once(TAA_MSG_SMT);
break;
case TAA_MITIGATION_TSX_DISABLED:
case TAA_MITIGATION_OFF:
break;
}
switch (mmio_mitigation) {
case MMIO_MITIGATION_VERW:
case MMIO_MITIGATION_UCODE_NEEDED:
if (sched_smt_active())
pr_warn_once(MMIO_MSG_SMT);
break;
case MMIO_MITIGATION_OFF:
break;
}
mutex_unlock(&spec_ctrl_mutex);
}
#undef pr_fmt
#define pr_fmt(fmt) "Speculative Store Bypass: " fmt
static enum ssb_mitigation ssb_mode __ro_after_init = SPEC_STORE_BYPASS_NONE;
/* The kernel command line selection */
enum ssb_mitigation_cmd {
SPEC_STORE_BYPASS_CMD_NONE,
SPEC_STORE_BYPASS_CMD_AUTO,
SPEC_STORE_BYPASS_CMD_ON,
SPEC_STORE_BYPASS_CMD_PRCTL,
SPEC_STORE_BYPASS_CMD_SECCOMP,
};
static const char * const ssb_strings[] = {
[SPEC_STORE_BYPASS_NONE] = "Vulnerable",
[SPEC_STORE_BYPASS_DISABLE] = "Mitigation: Speculative Store Bypass disabled",
[SPEC_STORE_BYPASS_PRCTL] = "Mitigation: Speculative Store Bypass disabled via prctl",
[SPEC_STORE_BYPASS_SECCOMP] = "Mitigation: Speculative Store Bypass disabled via prctl and seccomp",
};
static const struct {
const char *option;
enum ssb_mitigation_cmd cmd;
} ssb_mitigation_options[] __initconst = {
{ "auto", SPEC_STORE_BYPASS_CMD_AUTO }, /* Platform decides */
{ "on", SPEC_STORE_BYPASS_CMD_ON }, /* Disable Speculative Store Bypass */
{ "off", SPEC_STORE_BYPASS_CMD_NONE }, /* Don't touch Speculative Store Bypass */
{ "prctl", SPEC_STORE_BYPASS_CMD_PRCTL }, /* Disable Speculative Store Bypass via prctl */
{ "seccomp", SPEC_STORE_BYPASS_CMD_SECCOMP }, /* Disable Speculative Store Bypass via prctl and seccomp */
};
static enum ssb_mitigation_cmd __init ssb_parse_cmdline(void)
{
enum ssb_mitigation_cmd cmd;
char arg[20];
int ret, i;
cmd = IS_ENABLED(CONFIG_MITIGATION_SSB) ?
SPEC_STORE_BYPASS_CMD_AUTO : SPEC_STORE_BYPASS_CMD_NONE;
if (cmdline_find_option_bool(boot_command_line, "nospec_store_bypass_disable") ||
cpu_mitigations_off()) {
return SPEC_STORE_BYPASS_CMD_NONE;
} else {
ret = cmdline_find_option(boot_command_line, "spec_store_bypass_disable",
arg, sizeof(arg));
if (ret < 0)
return cmd;
for (i = 0; i < ARRAY_SIZE(ssb_mitigation_options); i++) {
if (!match_option(arg, ret, ssb_mitigation_options[i].option))
continue;
cmd = ssb_mitigation_options[i].cmd;
break;
}
if (i >= ARRAY_SIZE(ssb_mitigation_options)) {
pr_err("unknown option (%s). Switching to default mode\n", arg);
return cmd;
}
}
return cmd;
}
static enum ssb_mitigation __init __ssb_select_mitigation(void)
{
enum ssb_mitigation mode = SPEC_STORE_BYPASS_NONE;
enum ssb_mitigation_cmd cmd;
if (!boot_cpu_has(X86_FEATURE_SSBD))
return mode;
cmd = ssb_parse_cmdline();
if (!boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS) &&
(cmd == SPEC_STORE_BYPASS_CMD_NONE ||
cmd == SPEC_STORE_BYPASS_CMD_AUTO))
return mode;
switch (cmd) {
case SPEC_STORE_BYPASS_CMD_SECCOMP:
/*
* Choose prctl+seccomp as the default mode if seccomp is
* enabled.
*/
if (IS_ENABLED(CONFIG_SECCOMP))
mode = SPEC_STORE_BYPASS_SECCOMP;
else
mode = SPEC_STORE_BYPASS_PRCTL;
break;
case SPEC_STORE_BYPASS_CMD_ON:
mode = SPEC_STORE_BYPASS_DISABLE;
break;
case SPEC_STORE_BYPASS_CMD_AUTO:
case SPEC_STORE_BYPASS_CMD_PRCTL:
mode = SPEC_STORE_BYPASS_PRCTL;
break;
case SPEC_STORE_BYPASS_CMD_NONE:
break;
}
/*
* We have three CPU feature flags that are in play here:
* - X86_BUG_SPEC_STORE_BYPASS - CPU is susceptible.
* - X86_FEATURE_SSBD - CPU is able to turn off speculative store bypass
* - X86_FEATURE_SPEC_STORE_BYPASS_DISABLE - engage the mitigation
*/
if (mode == SPEC_STORE_BYPASS_DISABLE) {
setup_force_cpu_cap(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE);
/*
* Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD may
* use a completely different MSR and bit dependent on family.
*/
if (!static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) &&
!static_cpu_has(X86_FEATURE_AMD_SSBD)) {
x86_amd_ssb_disable();
} else {
x86_spec_ctrl_base |= SPEC_CTRL_SSBD;
update_spec_ctrl(x86_spec_ctrl_base);
}
}
return mode;
}
static void ssb_select_mitigation(void)
{
ssb_mode = __ssb_select_mitigation();
if (boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS))
pr_info("%s\n", ssb_strings[ssb_mode]);
}
#undef pr_fmt
#define pr_fmt(fmt) "Speculation prctl: " fmt
static void task_update_spec_tif(struct task_struct *tsk)
{
/* Force the update of the real TIF bits */
set_tsk_thread_flag(tsk, TIF_SPEC_FORCE_UPDATE);
/*
* Immediately update the speculation control MSRs for the current
* task, but for a non-current task delay setting the CPU
* mitigation until it is scheduled next.
*
* This can only happen for SECCOMP mitigation. For PRCTL it's
* always the current task.
*/
if (tsk == current)
speculation_ctrl_update_current();
}
static int l1d_flush_prctl_set(struct task_struct *task, unsigned long ctrl)
{
if (!static_branch_unlikely(&switch_mm_cond_l1d_flush))
return -EPERM;
switch (ctrl) {
case PR_SPEC_ENABLE:
set_ti_thread_flag(&task->thread_info, TIF_SPEC_L1D_FLUSH);
return 0;
case PR_SPEC_DISABLE:
clear_ti_thread_flag(&task->thread_info, TIF_SPEC_L1D_FLUSH);
return 0;
default:
return -ERANGE;
}
}
static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
{
if (ssb_mode != SPEC_STORE_BYPASS_PRCTL &&
ssb_mode != SPEC_STORE_BYPASS_SECCOMP)
return -ENXIO;
switch (ctrl) {
case PR_SPEC_ENABLE:
/* If speculation is force disabled, enable is not allowed */
if (task_spec_ssb_force_disable(task))
return -EPERM;
task_clear_spec_ssb_disable(task);
task_clear_spec_ssb_noexec(task);
task_update_spec_tif(task);
break;
case PR_SPEC_DISABLE:
task_set_spec_ssb_disable(task);
task_clear_spec_ssb_noexec(task);
task_update_spec_tif(task);
break;
case PR_SPEC_FORCE_DISABLE:
task_set_spec_ssb_disable(task);
task_set_spec_ssb_force_disable(task);
task_clear_spec_ssb_noexec(task);
task_update_spec_tif(task);
break;
case PR_SPEC_DISABLE_NOEXEC:
if (task_spec_ssb_force_disable(task))
return -EPERM;
task_set_spec_ssb_disable(task);
task_set_spec_ssb_noexec(task);
task_update_spec_tif(task);
break;
default:
return -ERANGE;
}
return 0;
}
static bool is_spec_ib_user_controlled(void)
{
return spectre_v2_user_ibpb == SPECTRE_V2_USER_PRCTL ||
spectre_v2_user_ibpb == SPECTRE_V2_USER_SECCOMP ||
spectre_v2_user_stibp == SPECTRE_V2_USER_PRCTL ||
spectre_v2_user_stibp == SPECTRE_V2_USER_SECCOMP;
}
static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
{
switch (ctrl) {
case PR_SPEC_ENABLE:
if (spectre_v2_user_ibpb == SPECTRE_V2_USER_NONE &&
spectre_v2_user_stibp == SPECTRE_V2_USER_NONE)
return 0;
/*
* With strict mode for both IBPB and STIBP, the instruction
* code paths avoid checking this task flag and instead,
* unconditionally run the instruction. However, STIBP and IBPB
* are independent and either can be set to conditionally
* enabled regardless of the mode of the other.
*
* If either is set to conditional, allow the task flag to be
* updated, unless it was force-disabled by a previous prctl
* call. Currently, this is possible on an AMD CPU which has the
* feature X86_FEATURE_AMD_STIBP_ALWAYS_ON. In this case, if the
* kernel is booted with 'spectre_v2_user=seccomp', then
* spectre_v2_user_ibpb == SPECTRE_V2_USER_SECCOMP and
* spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT_PREFERRED.
*/
if (!is_spec_ib_user_controlled() ||
task_spec_ib_force_disable(task))
return -EPERM;
task_clear_spec_ib_disable(task);
task_update_spec_tif(task);
break;
case PR_SPEC_DISABLE:
case PR_SPEC_FORCE_DISABLE:
/*
* Indirect branch speculation is always allowed when
* mitigation is force disabled.
*/
if (spectre_v2_user_ibpb == SPECTRE_V2_USER_NONE &&
spectre_v2_user_stibp == SPECTRE_V2_USER_NONE)
return -EPERM;
if (!is_spec_ib_user_controlled())
return 0;
task_set_spec_ib_disable(task);
if (ctrl == PR_SPEC_FORCE_DISABLE)
task_set_spec_ib_force_disable(task);
task_update_spec_tif(task);
if (task == current)
indirect_branch_prediction_barrier();
break;
default:
return -ERANGE;
}
return 0;
}
int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
unsigned long ctrl)
{
switch (which) {
case PR_SPEC_STORE_BYPASS:
return ssb_prctl_set(task, ctrl);
case PR_SPEC_INDIRECT_BRANCH:
return ib_prctl_set(task, ctrl);
case PR_SPEC_L1D_FLUSH:
return l1d_flush_prctl_set(task, ctrl);
default:
return -ENODEV;
}
}
#ifdef CONFIG_SECCOMP
void arch_seccomp_spec_mitigate(struct task_struct *task)
{
if (ssb_mode == SPEC_STORE_BYPASS_SECCOMP)
ssb_prctl_set(task, PR_SPEC_FORCE_DISABLE);
if (spectre_v2_user_ibpb == SPECTRE_V2_USER_SECCOMP ||
spectre_v2_user_stibp == SPECTRE_V2_USER_SECCOMP)
ib_prctl_set(task, PR_SPEC_FORCE_DISABLE);
}
#endif
static int l1d_flush_prctl_get(struct task_struct *task)
{
if (!static_branch_unlikely(&switch_mm_cond_l1d_flush))
return PR_SPEC_FORCE_DISABLE;
if (test_ti_thread_flag(&task->thread_info, TIF_SPEC_L1D_FLUSH))
return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
else
return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
}
static int ssb_prctl_get(struct task_struct *task)
{
switch (ssb_mode) {
case SPEC_STORE_BYPASS_NONE:
if (boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS))
return PR_SPEC_ENABLE;
return PR_SPEC_NOT_AFFECTED;
case SPEC_STORE_BYPASS_DISABLE:
return PR_SPEC_DISABLE;
case SPEC_STORE_BYPASS_SECCOMP:
case SPEC_STORE_BYPASS_PRCTL:
if (task_spec_ssb_force_disable(task))
return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE;
if (task_spec_ssb_noexec(task))
return PR_SPEC_PRCTL | PR_SPEC_DISABLE_NOEXEC;
if (task_spec_ssb_disable(task))
return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
}
BUG();
}
static int ib_prctl_get(struct task_struct *task)
{
if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
return PR_SPEC_NOT_AFFECTED;
if (spectre_v2_user_ibpb == SPECTRE_V2_USER_NONE &&
spectre_v2_user_stibp == SPECTRE_V2_USER_NONE)
return PR_SPEC_ENABLE;
else if (is_spec_ib_user_controlled()) {
if (task_spec_ib_force_disable(task))
return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE;
if (task_spec_ib_disable(task))
return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
} else if (spectre_v2_user_ibpb == SPECTRE_V2_USER_STRICT ||
spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT ||
spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT_PREFERRED)
return PR_SPEC_DISABLE;
else
return PR_SPEC_NOT_AFFECTED;
}
int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
{
switch (which) {
case PR_SPEC_STORE_BYPASS:
return ssb_prctl_get(task);
case PR_SPEC_INDIRECT_BRANCH:
return ib_prctl_get(task);
case PR_SPEC_L1D_FLUSH:
return l1d_flush_prctl_get(task);
default:
return -ENODEV;
}
}
void x86_spec_ctrl_setup_ap(void)
{
if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
update_spec_ctrl(x86_spec_ctrl_base);
if (ssb_mode == SPEC_STORE_BYPASS_DISABLE)
x86_amd_ssb_disable();
}
bool itlb_multihit_kvm_mitigation;
EXPORT_SYMBOL_GPL(itlb_multihit_kvm_mitigation);
#undef pr_fmt
#define pr_fmt(fmt) "L1TF: " fmt
/* Default mitigation for L1TF-affected CPUs */
enum l1tf_mitigations l1tf_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_L1TF) ? L1TF_MITIGATION_FLUSH : L1TF_MITIGATION_OFF;
#if IS_ENABLED(CONFIG_KVM_INTEL)
EXPORT_SYMBOL_GPL(l1tf_mitigation);
#endif
enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
EXPORT_SYMBOL_GPL(l1tf_vmx_mitigation);
/*
* These CPUs all support 44bits physical address space internally in the
* cache but CPUID can report a smaller number of physical address bits.
*
* The L1TF mitigation uses the top most address bit for the inversion of
* non present PTEs. When the installed memory reaches into the top most
* address bit due to memory holes, which has been observed on machines
* which report 36bits physical address bits and have 32G RAM installed,
* then the mitigation range check in l1tf_select_mitigation() triggers.
* This is a false positive because the mitigation is still possible due to
* the fact that the cache uses 44bit internally. Use the cache bits
* instead of the reported physical bits and adjust them on the affected
* machines to 44bit if the reported bits are less than 44.
*/
static void override_cache_bits(struct cpuinfo_x86 *c)
{
if (c->x86 != 6)
return;
switch (c->x86_vfm) {
case INTEL_NEHALEM:
case INTEL_WESTMERE:
case INTEL_SANDYBRIDGE:
case INTEL_IVYBRIDGE:
case INTEL_HASWELL:
case INTEL_HASWELL_L:
case INTEL_HASWELL_G:
case INTEL_BROADWELL:
case INTEL_BROADWELL_G:
case INTEL_SKYLAKE_L:
case INTEL_SKYLAKE:
case INTEL_KABYLAKE_L:
case INTEL_KABYLAKE:
if (c->x86_cache_bits < 44)
c->x86_cache_bits = 44;
break;
}
}
static void __init l1tf_select_mitigation(void)
{
u64 half_pa;
if (!boot_cpu_has_bug(X86_BUG_L1TF))
return;
if (cpu_mitigations_off())
l1tf_mitigation = L1TF_MITIGATION_OFF;
else if (cpu_mitigations_auto_nosmt())
l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT;
override_cache_bits(&boot_cpu_data);
switch (l1tf_mitigation) {
case L1TF_MITIGATION_OFF:
case L1TF_MITIGATION_FLUSH_NOWARN:
case L1TF_MITIGATION_FLUSH:
break;
case L1TF_MITIGATION_FLUSH_NOSMT:
case L1TF_MITIGATION_FULL:
cpu_smt_disable(false);
break;
case L1TF_MITIGATION_FULL_FORCE:
cpu_smt_disable(true);
break;
}
#if CONFIG_PGTABLE_LEVELS == 2
pr_warn("Kernel not compiled for PAE. No mitigation for L1TF\n");
return;
#endif
half_pa = (u64)l1tf_pfn_limit() << PAGE_SHIFT;
if (l1tf_mitigation != L1TF_MITIGATION_OFF &&
e820__mapped_any(half_pa, ULLONG_MAX - half_pa, E820_TYPE_RAM)) {
pr_warn("System has more than MAX_PA/2 memory. L1TF mitigation not effective.\n");
pr_info("You may make it effective by booting the kernel with mem=%llu parameter.\n",
half_pa);
pr_info("However, doing so will make a part of your RAM unusable.\n");
pr_info("Reading https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html might help you decide.\n");
return;
}
setup_force_cpu_cap(X86_FEATURE_L1TF_PTEINV);
}
static int __init l1tf_cmdline(char *str)
{
if (!boot_cpu_has_bug(X86_BUG_L1TF))
return 0;
if (!str)
return -EINVAL;
if (!strcmp(str, "off"))
l1tf_mitigation = L1TF_MITIGATION_OFF;
else if (!strcmp(str, "flush,nowarn"))
l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOWARN;
else if (!strcmp(str, "flush"))
l1tf_mitigation = L1TF_MITIGATION_FLUSH;
else if (!strcmp(str, "flush,nosmt"))
l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT;
else if (!strcmp(str, "full"))
l1tf_mitigation = L1TF_MITIGATION_FULL;
else if (!strcmp(str, "full,force"))
l1tf_mitigation = L1TF_MITIGATION_FULL_FORCE;
return 0;
}
early_param("l1tf", l1tf_cmdline);
#undef pr_fmt
#define pr_fmt(fmt) "Speculative Return Stack Overflow: " fmt
enum srso_mitigation {
SRSO_MITIGATION_NONE,
SRSO_MITIGATION_UCODE_NEEDED,
SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED,
SRSO_MITIGATION_MICROCODE,
SRSO_MITIGATION_SAFE_RET,
SRSO_MITIGATION_IBPB,
SRSO_MITIGATION_IBPB_ON_VMEXIT,
};
enum srso_mitigation_cmd {
SRSO_CMD_OFF,
SRSO_CMD_MICROCODE,
SRSO_CMD_SAFE_RET,
SRSO_CMD_IBPB,
SRSO_CMD_IBPB_ON_VMEXIT,
};
static const char * const srso_strings[] = {
[SRSO_MITIGATION_NONE] = "Vulnerable",
[SRSO_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode",
[SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED] = "Vulnerable: Safe RET, no microcode",
[SRSO_MITIGATION_MICROCODE] = "Vulnerable: Microcode, no safe RET",
[SRSO_MITIGATION_SAFE_RET] = "Mitigation: Safe RET",
[SRSO_MITIGATION_IBPB] = "Mitigation: IBPB",
[SRSO_MITIGATION_IBPB_ON_VMEXIT] = "Mitigation: IBPB on VMEXIT only"
};
static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_NONE;
static enum srso_mitigation_cmd srso_cmd __ro_after_init = SRSO_CMD_SAFE_RET;
static int __init srso_parse_cmdline(char *str)
{
if (!str)
return -EINVAL;
if (!strcmp(str, "off"))
srso_cmd = SRSO_CMD_OFF;
else if (!strcmp(str, "microcode"))
srso_cmd = SRSO_CMD_MICROCODE;
else if (!strcmp(str, "safe-ret"))
srso_cmd = SRSO_CMD_SAFE_RET;
else if (!strcmp(str, "ibpb"))
srso_cmd = SRSO_CMD_IBPB;
else if (!strcmp(str, "ibpb-vmexit"))
srso_cmd = SRSO_CMD_IBPB_ON_VMEXIT;
else
pr_err("Ignoring unknown SRSO option (%s).", str);
return 0;
}
early_param("spec_rstack_overflow", srso_parse_cmdline);
#define SRSO_NOTICE "WARNING: See https://kernel.org/doc/html/latest/admin-guide/hw-vuln/srso.html for mitigation options."
static void __init srso_select_mitigation(void)
{
bool has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE);
if (!boot_cpu_has_bug(X86_BUG_SRSO) ||
cpu_mitigations_off() ||
srso_cmd == SRSO_CMD_OFF) {
if (boot_cpu_has(X86_FEATURE_SBPB))
x86_pred_cmd = PRED_CMD_SBPB;
return;
}
if (has_microcode) {
/*
* Zen1/2 with SMT off aren't vulnerable after the right
* IBPB microcode has been applied.
*
* Zen1/2 don't have SBPB, no need to try to enable it here.
*/
if (boot_cpu_data.x86 < 0x19 && !cpu_smt_possible()) {
setup_force_cpu_cap(X86_FEATURE_SRSO_NO);
return;
}
if (retbleed_mitigation == RETBLEED_MITIGATION_IBPB) {
srso_mitigation = SRSO_MITIGATION_IBPB;
goto out;
}
} else {
pr_warn("IBPB-extending microcode not applied!\n");
pr_warn(SRSO_NOTICE);
/* may be overwritten by SRSO_CMD_SAFE_RET below */
srso_mitigation = SRSO_MITIGATION_UCODE_NEEDED;
}
switch (srso_cmd) {
case SRSO_CMD_MICROCODE:
if (has_microcode) {
srso_mitigation = SRSO_MITIGATION_MICROCODE;
pr_warn(SRSO_NOTICE);
}
break;
case SRSO_CMD_SAFE_RET:
if (IS_ENABLED(CONFIG_MITIGATION_SRSO)) {
/*
* Enable the return thunk for generated code
* like ftrace, static_call, etc.
*/
setup_force_cpu_cap(X86_FEATURE_RETHUNK);
setup_force_cpu_cap(X86_FEATURE_UNRET);
if (boot_cpu_data.x86 == 0x19) {
setup_force_cpu_cap(X86_FEATURE_SRSO_ALIAS);
x86_return_thunk = srso_alias_return_thunk;
} else {
setup_force_cpu_cap(X86_FEATURE_SRSO);
x86_return_thunk = srso_return_thunk;
}
if (has_microcode)
srso_mitigation = SRSO_MITIGATION_SAFE_RET;
else
srso_mitigation = SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED;
} else {
pr_err("WARNING: kernel not compiled with MITIGATION_SRSO.\n");
}
break;
case SRSO_CMD_IBPB:
if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY)) {
if (has_microcode) {
setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
srso_mitigation = SRSO_MITIGATION_IBPB;
/*
* IBPB on entry already obviates the need for
* software-based untraining so clear those in case some
* other mitigation like Retbleed has selected them.
*/
setup_clear_cpu_cap(X86_FEATURE_UNRET);
setup_clear_cpu_cap(X86_FEATURE_RETHUNK);
}
} else {
pr_err("WARNING: kernel not compiled with MITIGATION_IBPB_ENTRY.\n");
}
break;
case SRSO_CMD_IBPB_ON_VMEXIT:
if (IS_ENABLED(CONFIG_MITIGATION_SRSO)) {
if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) {
setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT;
/*
* There is no need for RSB filling: entry_ibpb() ensures
* all predictions, including the RSB, are invalidated,
* regardless of IBPB implementation.
*/
setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT);
}
} else {
pr_err("WARNING: kernel not compiled with MITIGATION_SRSO.\n");
}
break;
default:
break;
}
out:
pr_info("%s\n", srso_strings[srso_mitigation]);
}
#undef pr_fmt
#define pr_fmt(fmt) fmt
#ifdef CONFIG_SYSFS
#define L1TF_DEFAULT_MSG "Mitigation: PTE Inversion"
#if IS_ENABLED(CONFIG_KVM_INTEL)
static const char * const l1tf_vmx_states[] = {
[VMENTER_L1D_FLUSH_AUTO] = "auto",
[VMENTER_L1D_FLUSH_NEVER] = "vulnerable",
[VMENTER_L1D_FLUSH_COND] = "conditional cache flushes",
[VMENTER_L1D_FLUSH_ALWAYS] = "cache flushes",
[VMENTER_L1D_FLUSH_EPT_DISABLED] = "EPT disabled",
[VMENTER_L1D_FLUSH_NOT_REQUIRED] = "flush not necessary"
};
static ssize_t l1tf_show_state(char *buf)
{
if (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_AUTO)
return sysfs_emit(buf, "%s\n", L1TF_DEFAULT_MSG);
if (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_EPT_DISABLED ||
(l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_NEVER &&
sched_smt_active())) {
return sysfs_emit(buf, "%s; VMX: %s\n", L1TF_DEFAULT_MSG,
l1tf_vmx_states[l1tf_vmx_mitigation]);
}
return sysfs_emit(buf, "%s; VMX: %s, SMT %s\n", L1TF_DEFAULT_MSG,
l1tf_vmx_states[l1tf_vmx_mitigation],
sched_smt_active() ? "vulnerable" : "disabled");
}
static ssize_t itlb_multihit_show_state(char *buf)
{
if (!boot_cpu_has(X86_FEATURE_MSR_IA32_FEAT_CTL) ||
!boot_cpu_has(X86_FEATURE_VMX))
return sysfs_emit(buf, "KVM: Mitigation: VMX unsupported\n");
else if (!(cr4_read_shadow() & X86_CR4_VMXE))
return sysfs_emit(buf, "KVM: Mitigation: VMX disabled\n");
else if (itlb_multihit_kvm_mitigation)
return sysfs_emit(buf, "KVM: Mitigation: Split huge pages\n");
else
return sysfs_emit(buf, "KVM: Vulnerable\n");
}
#else
static ssize_t l1tf_show_state(char *buf)
{
return sysfs_emit(buf, "%s\n", L1TF_DEFAULT_MSG);
}
static ssize_t itlb_multihit_show_state(char *buf)
{
return sysfs_emit(buf, "Processor vulnerable\n");
}
#endif
static ssize_t mds_show_state(char *buf)
{
if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
return sysfs_emit(buf, "%s; SMT Host state unknown\n",
mds_strings[mds_mitigation]);
}
if (boot_cpu_has(X86_BUG_MSBDS_ONLY)) {
return sysfs_emit(buf, "%s; SMT %s\n", mds_strings[mds_mitigation],
(mds_mitigation == MDS_MITIGATION_OFF ? "vulnerable" :
sched_smt_active() ? "mitigated" : "disabled"));
}
return sysfs_emit(buf, "%s; SMT %s\n", mds_strings[mds_mitigation],
sched_smt_active() ? "vulnerable" : "disabled");
}
static ssize_t tsx_async_abort_show_state(char *buf)
{
if ((taa_mitigation == TAA_MITIGATION_TSX_DISABLED) ||
(taa_mitigation == TAA_MITIGATION_OFF))
return sysfs_emit(buf, "%s\n", taa_strings[taa_mitigation]);
if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
return sysfs_emit(buf, "%s; SMT Host state unknown\n",
taa_strings[taa_mitigation]);
}
return sysfs_emit(buf, "%s; SMT %s\n", taa_strings[taa_mitigation],
sched_smt_active() ? "vulnerable" : "disabled");
}
static ssize_t mmio_stale_data_show_state(char *buf)
{
if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN))
return sysfs_emit(buf, "Unknown: No mitigations\n");
if (mmio_mitigation == MMIO_MITIGATION_OFF)
return sysfs_emit(buf, "%s\n", mmio_strings[mmio_mitigation]);
if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
return sysfs_emit(buf, "%s; SMT Host state unknown\n",
mmio_strings[mmio_mitigation]);
}
return sysfs_emit(buf, "%s; SMT %s\n", mmio_strings[mmio_mitigation],
sched_smt_active() ? "vulnerable" : "disabled");
}
static ssize_t rfds_show_state(char *buf)
{
return sysfs_emit(buf, "%s\n", rfds_strings[rfds_mitigation]);
}
static char *stibp_state(void)
{
if (spectre_v2_in_eibrs_mode(spectre_v2_enabled) &&
!boot_cpu_has(X86_FEATURE_AUTOIBRS))
return "";
switch (spectre_v2_user_stibp) {
case SPECTRE_V2_USER_NONE:
return "; STIBP: disabled";
case SPECTRE_V2_USER_STRICT:
return "; STIBP: forced";
case SPECTRE_V2_USER_STRICT_PREFERRED:
return "; STIBP: always-on";
case SPECTRE_V2_USER_PRCTL:
case SPECTRE_V2_USER_SECCOMP:
if (static_key_enabled(&switch_to_cond_stibp))
return "; STIBP: conditional";
}
return "";
}
static char *ibpb_state(void)
{
if (boot_cpu_has(X86_FEATURE_IBPB)) {
if (static_key_enabled(&switch_mm_always_ibpb))
return "; IBPB: always-on";
if (static_key_enabled(&switch_mm_cond_ibpb))
return "; IBPB: conditional";
return "; IBPB: disabled";
}
return "";
}
static char *pbrsb_eibrs_state(void)
{
if (boot_cpu_has_bug(X86_BUG_EIBRS_PBRSB)) {
if (boot_cpu_has(X86_FEATURE_RSB_VMEXIT_LITE) ||
boot_cpu_has(X86_FEATURE_RSB_VMEXIT))
return "; PBRSB-eIBRS: SW sequence";
else
return "; PBRSB-eIBRS: Vulnerable";
} else {
return "; PBRSB-eIBRS: Not affected";
}
}
static const char *spectre_bhi_state(void)
{
if (!boot_cpu_has_bug(X86_BUG_BHI))
return "; BHI: Not affected";
else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_HW))
return "; BHI: BHI_DIS_S";
else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP))
return "; BHI: SW loop, KVM: SW loop";
else if (boot_cpu_has(X86_FEATURE_RETPOLINE) &&
!boot_cpu_has(X86_FEATURE_RETPOLINE_LFENCE) &&
rrsba_disabled)
return "; BHI: Retpoline";
else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT))
return "; BHI: Vulnerable, KVM: SW loop";
return "; BHI: Vulnerable";
}
static ssize_t spectre_v2_show_state(char *buf)
{
if (spectre_v2_enabled == SPECTRE_V2_LFENCE)
return sysfs_emit(buf, "Vulnerable: LFENCE\n");
if (spectre_v2_enabled == SPECTRE_V2_EIBRS && unprivileged_ebpf_enabled())
return sysfs_emit(buf, "Vulnerable: eIBRS with unprivileged eBPF\n");
if (sched_smt_active() && unprivileged_ebpf_enabled() &&
spectre_v2_enabled == SPECTRE_V2_EIBRS_LFENCE)
return sysfs_emit(buf, "Vulnerable: eIBRS+LFENCE with unprivileged eBPF and SMT\n");
return sysfs_emit(buf, "%s%s%s%s%s%s%s%s\n",
spectre_v2_strings[spectre_v2_enabled],
ibpb_state(),
boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? "; IBRS_FW" : "",
stibp_state(),
boot_cpu_has(X86_FEATURE_RSB_CTXSW) ? "; RSB filling" : "",
pbrsb_eibrs_state(),
spectre_bhi_state(),
/* this should always be at the end */
spectre_v2_module_string());
}
static ssize_t srbds_show_state(char *buf)
{
return sysfs_emit(buf, "%s\n", srbds_strings[srbds_mitigation]);
}
static ssize_t retbleed_show_state(char *buf)
{
if (retbleed_mitigation == RETBLEED_MITIGATION_UNRET ||
retbleed_mitigation == RETBLEED_MITIGATION_IBPB) {
if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
return sysfs_emit(buf, "Vulnerable: untrained return thunk / IBPB on non-AMD based uarch\n");
return sysfs_emit(buf, "%s; SMT %s\n", retbleed_strings[retbleed_mitigation],
!sched_smt_active() ? "disabled" :
spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT ||
spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT_PREFERRED ?
"enabled with STIBP protection" : "vulnerable");
}
return sysfs_emit(buf, "%s\n", retbleed_strings[retbleed_mitigation]);
}
static ssize_t srso_show_state(char *buf)
{
if (boot_cpu_has(X86_FEATURE_SRSO_NO))
return sysfs_emit(buf, "Mitigation: SMT disabled\n");
return sysfs_emit(buf, "%s\n", srso_strings[srso_mitigation]);
}
static ssize_t gds_show_state(char *buf)
{
return sysfs_emit(buf, "%s\n", gds_strings[gds_mitigation]);
}
static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,
char *buf, unsigned int bug)
{
if (!boot_cpu_has_bug(bug))
return sysfs_emit(buf, "Not affected\n");
switch (bug) {
case X86_BUG_CPU_MELTDOWN:
if (boot_cpu_has(X86_FEATURE_PTI))
return sysfs_emit(buf, "Mitigation: PTI\n");
if (hypervisor_is_type(X86_HYPER_XEN_PV))
return sysfs_emit(buf, "Unknown (XEN PV detected, hypervisor mitigation required)\n");
break;
case X86_BUG_SPECTRE_V1:
return sysfs_emit(buf, "%s\n", spectre_v1_strings[spectre_v1_mitigation]);
case X86_BUG_SPECTRE_V2:
return spectre_v2_show_state(buf);
case X86_BUG_SPEC_STORE_BYPASS:
return sysfs_emit(buf, "%s\n", ssb_strings[ssb_mode]);
case X86_BUG_L1TF:
if (boot_cpu_has(X86_FEATURE_L1TF_PTEINV))
return l1tf_show_state(buf);
break;
case X86_BUG_MDS:
return mds_show_state(buf);
case X86_BUG_TAA:
return tsx_async_abort_show_state(buf);
case X86_BUG_ITLB_MULTIHIT:
return itlb_multihit_show_state(buf);
case X86_BUG_SRBDS:
return srbds_show_state(buf);
case X86_BUG_MMIO_STALE_DATA:
case X86_BUG_MMIO_UNKNOWN:
return mmio_stale_data_show_state(buf);
case X86_BUG_RETBLEED:
return retbleed_show_state(buf);
case X86_BUG_SRSO:
return srso_show_state(buf);
case X86_BUG_GDS:
return gds_show_state(buf);
case X86_BUG_RFDS:
return rfds_show_state(buf);
default:
break;
}
return sysfs_emit(buf, "Vulnerable\n");
}
ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_CPU_MELTDOWN);
}
ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_SPECTRE_V1);
}
ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_SPECTRE_V2);
}
ssize_t cpu_show_spec_store_bypass(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_SPEC_STORE_BYPASS);
}
ssize_t cpu_show_l1tf(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_L1TF);
}
ssize_t cpu_show_mds(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_MDS);
}
ssize_t cpu_show_tsx_async_abort(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_TAA);
}
ssize_t cpu_show_itlb_multihit(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_ITLB_MULTIHIT);
}
ssize_t cpu_show_srbds(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_SRBDS);
}
ssize_t cpu_show_mmio_stale_data(struct device *dev, struct device_attribute *attr, char *buf)
{
if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN))
return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_UNKNOWN);
else
return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_STALE_DATA);
}
ssize_t cpu_show_retbleed(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_RETBLEED);
}
ssize_t cpu_show_spec_rstack_overflow(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_SRSO);
}
ssize_t cpu_show_gds(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_GDS);
}
ssize_t cpu_show_reg_file_data_sampling(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_RFDS);
}
#endif
void __warn_thunk(void)
{
WARN_ONCE(1, "Unpatched return thunk in use. This should not happen!\n");
}
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