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x86/bugs: Fix BHI handling of RRSBA

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The ARCH_CAP_RRSBA check isn't correct: RRSBA may have already been
disabled by the Spectre v2 mitigation (or can otherwise be disabled by
the BHI mitigation itself if needed).  In that case retpolines are fine.

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/6f56f13da34a0834b69163467449be7f58f253dc.1712813475.git.jpoimboe@kernel.org
This commit is contained in:
Josh Poimboeuf 2024-04-10 22:40:47 -07:00 committed by Ingo Molnar
parent d0485730d2
commit 1cea8a280d
1 changed files with 18 additions and 12 deletions
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30
arch/x86/kernel/cpu/bugs.c
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@ -1538,20 +1538,25 @@ static enum spectre_v2_mitigation __init spectre_v2_select_retpoline(void)
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)
{
u64 x86_arch_cap_msr;
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_arch_cap_msr = x86_read_arch_cap_msr();
if (x86_arch_cap_msr & ARCH_CAP_RRSBA) {
x86_spec_ctrl_base |= SPEC_CTRL_RRSBA_DIS_S;
update_spec_ctrl(x86_spec_ctrl_base);
}
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)
@ -1652,9 +1657,11 @@ static void __init bhi_select_mitigation(void)
return;
/* Retpoline mitigates against BHI unless the CPU has RRSBA behavior */
if (cpu_feature_enabled(X86_FEATURE_RETPOLINE) &&
!(x86_read_arch_cap_msr() & ARCH_CAP_RRSBA))
return;
if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) {
spec_ctrl_disable_kernel_rrsba();
if (rrsba_disabled)
return;
}
if (spec_ctrl_bhi_dis())
return;
@ -2809,8 +2816,7 @@ static const char *spectre_bhi_state(void)
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) &&
!(x86_arch_cap_msr & ARCH_CAP_RRSBA))
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";