x86/bugs: Clarify that syscall hardening isn't a BHI mitigation
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
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@ -441,10 +441,10 @@ The possible values in this file are:
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- System is protected by BHI_DIS_S
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* - BHI: SW loop, KVM SW loop
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- System is protected by software clearing sequence
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* - BHI: Syscall hardening
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- Syscalls are hardened against BHI
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* - BHI: Syscall hardening, KVM: SW loop
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- System is protected from userspace attacks by syscall hardening; KVM is protected by software clearing sequence
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* - BHI: Vulnerable
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- System is vulnerable to BHI
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* - BHI: Vulnerable, KVM: SW loop
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- System is vulnerable; KVM is protected by software clearing sequence
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Full mitigation might require a microcode update from the CPU
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vendor. When the necessary microcode is not available, the kernel will
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@ -661,8 +661,7 @@ kernel command line.
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spectre_bhi=
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[X86] Control mitigation of Branch History Injection
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(BHI) vulnerability. Syscalls are hardened against BHI
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regardless of this setting. This setting affects the deployment
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(BHI) vulnerability. This setting affects the deployment
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of the HW BHI control and the SW BHB clearing sequence.
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on
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@ -6065,8 +6065,7 @@
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See Documentation/admin-guide/laptops/sonypi.rst
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spectre_bhi= [X86] Control mitigation of Branch History Injection
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(BHI) vulnerability. Syscalls are hardened against BHI
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reglardless of this setting. This setting affects the
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(BHI) vulnerability. This setting affects the
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deployment of the HW BHI control and the SW BHB
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clearing sequence.
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@ -2819,9 +2819,9 @@ static const char *spectre_bhi_state(void)
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else if (boot_cpu_has(X86_FEATURE_RETPOLINE) && rrsba_disabled)
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return "; BHI: Retpoline";
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else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT))
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return "; BHI: Syscall hardening, KVM: SW loop";
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return "; BHI: Vulnerable, KVM: SW loop";
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return "; BHI: Vulnerable (Syscall hardening enabled)";
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return "; BHI: Vulnerable";
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}
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static ssize_t spectre_v2_show_state(char *buf)
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