Messages in this thread Patch in this message | | | From | Josh Poimboeuf <> | Subject | [PATCH 3/7] x86/bugs: Fix BHI handling of RRSBA | Date | Wed, 10 Apr 2024 22:40:47 -0700 |
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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: ec9404e40e8f ("x86/bhi: Add BHI mitigation knob") Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> --- arch/x86/kernel/cpu/bugs.c | 30 ++++++++++++++++++------------ 1 file changed, 18 insertions(+), 12 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 27d6d64eeec3..0755600d5d18 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -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 ia32_cap; + if (rrsba_disabled) + return; + + if (!(ia32_cap & ARCH_CAP_RRSBA)) { + rrsba_disabled = true; + return; + } if (!boot_cpu_has(X86_FEATURE_RRSBA_CTRL)) return; - ia32_cap = x86_read_arch_cap_msr(); - - if (ia32_cap & 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 * const 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) && - !(ia32_cap & 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"; -- 2.44.0
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