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linux/arch/riscv/kernel/entry.S
Jisheng Zhang 8f1534e744
riscv: avoid Imbalance in RAS 
Inspired by[1], modify the code to remove the code of modifying ra to
avoid imbalance RAS (return address stack) which may lead to incorret
predictions on return.

Link: https://lore.kernel.org/linux-riscv/20240607061335.2197383-1-cyrilbur@tenstorrent.com/ [1]
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Cyril Bur <cyrilbur@tenstorrent.com>
Link: https://lore.kernel.org/r/20240720170659.1522-1-jszhang@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2024-09-15 20:58:25 -07:00

456 lines
12 KiB
ArmAsm
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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Copyright (C) 2012 Regents of the University of California
* Copyright (C) 2017 SiFive
*/
#include <linux/init.h>
#include <linux/linkage.h>
#include <asm/asm.h>
#include <asm/csr.h>
#include <asm/scs.h>
#include <asm/unistd.h>
#include <asm/page.h>
#include <asm/thread_info.h>
#include <asm/asm-offsets.h>
#include <asm/errata_list.h>
#include <linux/sizes.h>
.section .irqentry.text, "ax"
.macro new_vmalloc_check
REG_S a0, TASK_TI_A0(tp)
csrr a0, CSR_CAUSE
/* Exclude IRQs */
blt a0, zero, _new_vmalloc_restore_context_a0
REG_S a1, TASK_TI_A1(tp)
/* Only check new_vmalloc if we are in page/protection fault */
li a1, EXC_LOAD_PAGE_FAULT
beq a0, a1, _new_vmalloc_kernel_address
li a1, EXC_STORE_PAGE_FAULT
beq a0, a1, _new_vmalloc_kernel_address
li a1, EXC_INST_PAGE_FAULT
bne a0, a1, _new_vmalloc_restore_context_a1
_new_vmalloc_kernel_address:
/* Is it a kernel address? */
csrr a0, CSR_TVAL
bge a0, zero, _new_vmalloc_restore_context_a1
/* Check if a new vmalloc mapping appeared that could explain the trap */
REG_S a2, TASK_TI_A2(tp)
/*
* Computes:
* a0 = &new_vmalloc[BIT_WORD(cpu)]
* a1 = BIT_MASK(cpu)
*/
REG_L a2, TASK_TI_CPU(tp)
/*
* Compute the new_vmalloc element position:
* (cpu / 64) * 8 = (cpu >> 6) << 3
*/
srli a1, a2, 6
slli a1, a1, 3
la a0, new_vmalloc
add a0, a0, a1
/*
* Compute the bit position in the new_vmalloc element:
* bit_pos = cpu % 64 = cpu - (cpu / 64) * 64 = cpu - (cpu >> 6) << 6
* = cpu - ((cpu >> 6) << 3) << 3
*/
slli a1, a1, 3
sub a1, a2, a1
/* Compute the "get mask": 1 << bit_pos */
li a2, 1
sll a1, a2, a1
/* Check the value of new_vmalloc for this cpu */
REG_L a2, 0(a0)
and a2, a2, a1
beq a2, zero, _new_vmalloc_restore_context
/* Atomically reset the current cpu bit in new_vmalloc */
amoxor.d a0, a1, (a0)
/* Only emit a sfence.vma if the uarch caches invalid entries */
ALTERNATIVE("sfence.vma", "nop", 0, RISCV_ISA_EXT_SVVPTC, 1)
REG_L a0, TASK_TI_A0(tp)
REG_L a1, TASK_TI_A1(tp)
REG_L a2, TASK_TI_A2(tp)
csrw CSR_SCRATCH, x0
sret
_new_vmalloc_restore_context:
REG_L a2, TASK_TI_A2(tp)
_new_vmalloc_restore_context_a1:
REG_L a1, TASK_TI_A1(tp)
_new_vmalloc_restore_context_a0:
REG_L a0, TASK_TI_A0(tp)
.endm
SYM_CODE_START(handle_exception)
/*
* If coming from userspace, preserve the user thread pointer and load
* the kernel thread pointer. If we came from the kernel, the scratch
* register will contain 0, and we should continue on the current TP.
*/
csrrw tp, CSR_SCRATCH, tp
bnez tp, .Lsave_context
.Lrestore_kernel_tpsp:
csrr tp, CSR_SCRATCH
#ifdef CONFIG_64BIT
/*
* The RISC-V kernel does not eagerly emit a sfence.vma after each
* new vmalloc mapping, which may result in exceptions:
* - if the uarch caches invalid entries, the new mapping would not be
* observed by the page table walker and an invalidation is needed.
* - if the uarch does not cache invalid entries, a reordered access
* could "miss" the new mapping and traps: in that case, we only need
* to retry the access, no sfence.vma is required.
*/
new_vmalloc_check
#endif
REG_S sp, TASK_TI_KERNEL_SP(tp)
#ifdef CONFIG_VMAP_STACK
addi sp, sp, -(PT_SIZE_ON_STACK)
srli sp, sp, THREAD_SHIFT
andi sp, sp, 0x1
bnez sp, handle_kernel_stack_overflow
REG_L sp, TASK_TI_KERNEL_SP(tp)
#endif
.Lsave_context:
REG_S sp, TASK_TI_USER_SP(tp)
REG_L sp, TASK_TI_KERNEL_SP(tp)
addi sp, sp, -(PT_SIZE_ON_STACK)
REG_S x1, PT_RA(sp)
REG_S x3, PT_GP(sp)
REG_S x5, PT_T0(sp)
save_from_x6_to_x31
/*
* Disable user-mode memory access as it should only be set in the
* actual user copy routines.
*
* Disable the FPU/Vector to detect illegal usage of floating point
* or vector in kernel space.
*/
li t0, SR_SUM | SR_FS_VS
REG_L s0, TASK_TI_USER_SP(tp)
csrrc s1, CSR_STATUS, t0
csrr s2, CSR_EPC
csrr s3, CSR_TVAL
csrr s4, CSR_CAUSE
csrr s5, CSR_SCRATCH
REG_S s0, PT_SP(sp)
REG_S s1, PT_STATUS(sp)
REG_S s2, PT_EPC(sp)
REG_S s3, PT_BADADDR(sp)
REG_S s4, PT_CAUSE(sp)
REG_S s5, PT_TP(sp)
/*
* Set the scratch register to 0, so that if a recursive exception
* occurs, the exception vector knows it came from the kernel
*/
csrw CSR_SCRATCH, x0
/* Load the global pointer */
load_global_pointer
/* Load the kernel shadow call stack pointer if coming from userspace */
scs_load_current_if_task_changed s5
#ifdef CONFIG_RISCV_ISA_V_PREEMPTIVE
move a0, sp
call riscv_v_context_nesting_start
#endif
move a0, sp /* pt_regs */
/*
* MSB of cause differentiates between
* interrupts and exceptions
*/
bge s4, zero, 1f
/* Handle interrupts */
call do_irq
j ret_from_exception
1:
/* Handle other exceptions */
slli t0, s4, RISCV_LGPTR
la t1, excp_vect_table
la t2, excp_vect_table_end
add t0, t1, t0
/* Check if exception code lies within bounds */
bgeu t0, t2, 3f
REG_L t1, 0(t0)
2: jalr t1
j ret_from_exception
3:
la t1, do_trap_unknown
j 2b
SYM_CODE_END(handle_exception)
ASM_NOKPROBE(handle_exception)
/*
* The ret_from_exception must be called with interrupt disabled. Here is the
* caller list:
* - handle_exception
* - ret_from_fork
*/
SYM_CODE_START_NOALIGN(ret_from_exception)
REG_L s0, PT_STATUS(sp)
#ifdef CONFIG_RISCV_M_MODE
/* the MPP value is too large to be used as an immediate arg for addi */
li t0, SR_MPP
and s0, s0, t0
#else
andi s0, s0, SR_SPP
#endif
bnez s0, 1f
#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
call stackleak_erase_on_task_stack
#endif
/* Save unwound kernel stack pointer in thread_info */
addi s0, sp, PT_SIZE_ON_STACK
REG_S s0, TASK_TI_KERNEL_SP(tp)
/* Save the kernel shadow call stack pointer */
scs_save_current
/*
* Save TP into the scratch register , so we can find the kernel data
* structures again.
*/
csrw CSR_SCRATCH, tp
1:
#ifdef CONFIG_RISCV_ISA_V_PREEMPTIVE
move a0, sp
call riscv_v_context_nesting_end
#endif
REG_L a0, PT_STATUS(sp)
/*
* The current load reservation is effectively part of the processor's
* state, in the sense that load reservations cannot be shared between
* different hart contexts. We can't actually save and restore a load
* reservation, so instead here we clear any existing reservation --
* it's always legal for implementations to clear load reservations at
* any point (as long as the forward progress guarantee is kept, but
* we'll ignore that here).
*
* Dangling load reservations can be the result of taking a trap in the
* middle of an LR/SC sequence, but can also be the result of a taken
* forward branch around an SC -- which is how we implement CAS. As a
* result we need to clear reservations between the last CAS and the
* jump back to the new context. While it is unlikely the store
* completes, implementations are allowed to expand reservations to be
* arbitrarily large.
*/
REG_L a2, PT_EPC(sp)
REG_SC x0, a2, PT_EPC(sp)
csrw CSR_STATUS, a0
csrw CSR_EPC, a2
REG_L x1, PT_RA(sp)
REG_L x3, PT_GP(sp)
REG_L x4, PT_TP(sp)
REG_L x5, PT_T0(sp)
restore_from_x6_to_x31
REG_L x2, PT_SP(sp)
#ifdef CONFIG_RISCV_M_MODE
mret
#else
sret
#endif
SYM_CODE_END(ret_from_exception)
ASM_NOKPROBE(ret_from_exception)
#ifdef CONFIG_VMAP_STACK
SYM_CODE_START_LOCAL(handle_kernel_stack_overflow)
/* we reach here from kernel context, sscratch must be 0 */
csrrw x31, CSR_SCRATCH, x31
asm_per_cpu sp, overflow_stack, x31
li x31, OVERFLOW_STACK_SIZE
add sp, sp, x31
/* zero out x31 again and restore x31 */
xor x31, x31, x31
csrrw x31, CSR_SCRATCH, x31
addi sp, sp, -(PT_SIZE_ON_STACK)
//save context to overflow stack
REG_S x1, PT_RA(sp)
REG_S x3, PT_GP(sp)
REG_S x5, PT_T0(sp)
save_from_x6_to_x31
REG_L s0, TASK_TI_KERNEL_SP(tp)
csrr s1, CSR_STATUS
csrr s2, CSR_EPC
csrr s3, CSR_TVAL
csrr s4, CSR_CAUSE
csrr s5, CSR_SCRATCH
REG_S s0, PT_SP(sp)
REG_S s1, PT_STATUS(sp)
REG_S s2, PT_EPC(sp)
REG_S s3, PT_BADADDR(sp)
REG_S s4, PT_CAUSE(sp)
REG_S s5, PT_TP(sp)
move a0, sp
tail handle_bad_stack
SYM_CODE_END(handle_kernel_stack_overflow)
ASM_NOKPROBE(handle_kernel_stack_overflow)
#endif
SYM_CODE_START(ret_from_fork)
call schedule_tail
beqz s0, 1f /* not from kernel thread */
/* Call fn(arg) */
move a0, s1
jalr s0
1:
move a0, sp /* pt_regs */
call syscall_exit_to_user_mode
j ret_from_exception
SYM_CODE_END(ret_from_fork)
#ifdef CONFIG_IRQ_STACKS
/*
* void call_on_irq_stack(struct pt_regs *regs,
* void (*func)(struct pt_regs *));
*
* Calls func(regs) using the per-CPU IRQ stack.
*/
SYM_FUNC_START(call_on_irq_stack)
/* Create a frame record to save ra and s0 (fp) */
addi sp, sp, -STACKFRAME_SIZE_ON_STACK
REG_S ra, STACKFRAME_RA(sp)
REG_S s0, STACKFRAME_FP(sp)
addi s0, sp, STACKFRAME_SIZE_ON_STACK
/* Switch to the per-CPU shadow call stack */
scs_save_current
scs_load_irq_stack t0
/* Switch to the per-CPU IRQ stack and call the handler */
load_per_cpu t0, irq_stack_ptr, t1
li t1, IRQ_STACK_SIZE
add sp, t0, t1
jalr a1
/* Switch back to the thread shadow call stack */
scs_load_current
/* Switch back to the thread stack and restore ra and s0 */
addi sp, s0, -STACKFRAME_SIZE_ON_STACK
REG_L ra, STACKFRAME_RA(sp)
REG_L s0, STACKFRAME_FP(sp)
addi sp, sp, STACKFRAME_SIZE_ON_STACK
ret
SYM_FUNC_END(call_on_irq_stack)
#endif /* CONFIG_IRQ_STACKS */
/*
* Integer register context switch
* The callee-saved registers must be saved and restored.
*
* a0: previous task_struct (must be preserved across the switch)
* a1: next task_struct
*
* The value of a0 and a1 must be preserved by this function, as that's how
* arguments are passed to schedule_tail.
*/
SYM_FUNC_START(__switch_to)
/* Save context into prev->thread */
li a4, TASK_THREAD_RA
add a3, a0, a4
add a4, a1, a4
REG_S ra, TASK_THREAD_RA_RA(a3)
REG_S sp, TASK_THREAD_SP_RA(a3)
REG_S s0, TASK_THREAD_S0_RA(a3)
REG_S s1, TASK_THREAD_S1_RA(a3)
REG_S s2, TASK_THREAD_S2_RA(a3)
REG_S s3, TASK_THREAD_S3_RA(a3)
REG_S s4, TASK_THREAD_S4_RA(a3)
REG_S s5, TASK_THREAD_S5_RA(a3)
REG_S s6, TASK_THREAD_S6_RA(a3)
REG_S s7, TASK_THREAD_S7_RA(a3)
REG_S s8, TASK_THREAD_S8_RA(a3)
REG_S s9, TASK_THREAD_S9_RA(a3)
REG_S s10, TASK_THREAD_S10_RA(a3)
REG_S s11, TASK_THREAD_S11_RA(a3)
/* Save the kernel shadow call stack pointer */
scs_save_current
/* Restore context from next->thread */
REG_L ra, TASK_THREAD_RA_RA(a4)
REG_L sp, TASK_THREAD_SP_RA(a4)
REG_L s0, TASK_THREAD_S0_RA(a4)
REG_L s1, TASK_THREAD_S1_RA(a4)
REG_L s2, TASK_THREAD_S2_RA(a4)
REG_L s3, TASK_THREAD_S3_RA(a4)
REG_L s4, TASK_THREAD_S4_RA(a4)
REG_L s5, TASK_THREAD_S5_RA(a4)
REG_L s6, TASK_THREAD_S6_RA(a4)
REG_L s7, TASK_THREAD_S7_RA(a4)
REG_L s8, TASK_THREAD_S8_RA(a4)
REG_L s9, TASK_THREAD_S9_RA(a4)
REG_L s10, TASK_THREAD_S10_RA(a4)
REG_L s11, TASK_THREAD_S11_RA(a4)
/* The offset of thread_info in task_struct is zero. */
move tp, a1
/* Switch to the next shadow call stack */
scs_load_current
ret
SYM_FUNC_END(__switch_to)
#ifndef CONFIG_MMU
#define do_page_fault do_trap_unknown
#endif
.section ".rodata"
.align LGREG
/* Exception vector table */
SYM_DATA_START_LOCAL(excp_vect_table)
RISCV_PTR do_trap_insn_misaligned
ALT_INSN_FAULT(RISCV_PTR do_trap_insn_fault)
RISCV_PTR do_trap_insn_illegal
RISCV_PTR do_trap_break
RISCV_PTR do_trap_load_misaligned
RISCV_PTR do_trap_load_fault
RISCV_PTR do_trap_store_misaligned
RISCV_PTR do_trap_store_fault
RISCV_PTR do_trap_ecall_u /* system call */
RISCV_PTR do_trap_ecall_s
RISCV_PTR do_trap_unknown
RISCV_PTR do_trap_ecall_m
/* instruciton page fault */
ALT_PAGE_FAULT(RISCV_PTR do_page_fault)
RISCV_PTR do_page_fault /* load page fault */
RISCV_PTR do_trap_unknown
RISCV_PTR do_page_fault /* store page fault */
SYM_DATA_END_LABEL(excp_vect_table, SYM_L_LOCAL, excp_vect_table_end)
#ifndef CONFIG_MMU
SYM_DATA_START(__user_rt_sigreturn)
li a7, __NR_rt_sigreturn
ecall
SYM_DATA_END(__user_rt_sigreturn)
#endif
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