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x86/bugs: Clarify that syscall hardening isn't a BHI mitigation

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While syscall hardening helps prevent some BHI attacks, there's still
other low-hanging fruit remaining.  Don't classify it as a mitigation
and make it clear that the system may still be vulnerable if it doesn't
have a HW or SW mitigation enabled.

Fixes: ec9404e40e ("x86/bhi: Add BHI mitigation knob")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/b5951dae3fdee7f1520d5136a27be3bdfe95f88b.1712813475.git.jpoimboe@kernel.org
This commit is contained in:
Josh Poimboeuf 2024-04-10 22:40:48 -07:00 committed by Ingo Molnar
parent 1cea8a280d
commit 5f882f3b0a
3 changed files with 9 additions and 11 deletions
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11
Documentation/admin-guide/hw-vuln/spectre.rst
View File

@ -441,10 +441,10 @@ The possible values in this file are:
- System is protected by BHI_DIS_S
* - BHI: SW loop, KVM SW loop
- System is protected by software clearing sequence
* - BHI: Syscall hardening
- Syscalls are hardened against BHI
* - BHI: Syscall hardening, KVM: SW loop
- System is protected from userspace attacks by syscall hardening; KVM is protected by software clearing sequence
* - BHI: Vulnerable
- System is vulnerable to BHI
* - BHI: Vulnerable, KVM: SW loop
- System is vulnerable; KVM is protected by software clearing sequence
Full mitigation might require a microcode update from the CPU
vendor. When the necessary microcode is not available, the kernel will
@ -661,8 +661,7 @@ kernel command line.
spectre_bhi=
[X86] Control mitigation of Branch History Injection
(BHI) vulnerability. Syscalls are hardened against BHI
regardless of this setting. This setting affects the deployment
(BHI) vulnerability. This setting affects the deployment
of the HW BHI control and the SW BHB clearing sequence.
on

3
Documentation/admin-guide/kernel-parameters.txt
View File

@ -6065,8 +6065,7 @@
See Documentation/admin-guide/laptops/sonypi.rst
spectre_bhi= [X86] Control mitigation of Branch History Injection
(BHI) vulnerability. Syscalls are hardened against BHI
reglardless of this setting. This setting affects the
(BHI) vulnerability. This setting affects the
deployment of the HW BHI control and the SW BHB
clearing sequence.

6
arch/x86/kernel/cpu/bugs.c
View File

@ -2818,10 +2818,10 @@ static const char *spectre_bhi_state(void)
return "; BHI: SW loop, KVM: SW loop";
else if (boot_cpu_has(X86_FEATURE_RETPOLINE) && rrsba_disabled)
return "; BHI: Retpoline";
else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT))
return "; BHI: Syscall hardening, KVM: SW loop";
else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT))
return "; BHI: Vulnerable, KVM: SW loop";
return "; BHI: Vulnerable (Syscall hardening enabled)";
return "; BHI: Vulnerable";
}
static ssize_t spectre_v2_show_state(char *buf)