[PATCH 6.8 085/158] x86/bugs: Fix BHI retpoline check

Greg Kroah-Hartman
2024-04-23T21:42:01Z

From: Josh Poimboeuf <jpoimboe@kernel.org>

[ Upstream commit 69129794d94c544810e68b2b4eaa7e44063f9bf2 ]

Confusingly, X86_FEATURE_RETPOLINE doesn't mean retpolines are enabled,
as it also includes the original "AMD retpoline" which isn't a retpoline
at all.

Also replace cpu_feature_enabled() with boot_cpu_has() because this is
before alternatives are patched and cpu_feature_enabled()'s fallback
path is slower than plain old boot_cpu_has().

Fixes: ec9404e40e8f ("x86/bhi: Add BHI mitigation knob")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/ad3807424a3953f0323c011a643405619f2a4927.1712944776.git.jpoimboe@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/kernel/cpu/bugs.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index cbc8c88144e47..e7ceee008bd09 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1651,7 +1651,8 @@ 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)) {
+ if (boot_cpu_has(X86_FEATURE_RETPOLINE) &&
+ !boot_cpu_has(X86_FEATURE_RETPOLINE_LFENCE)) {
spec_ctrl_disable_kernel_rrsba();
if (rrsba_disabled)
return;
@@ -2803,11 +2804,13 @@ static const char *spectre_bhi_state(void)
{
if (!boot_cpu_has_bug(X86_BUG_BHI))
return "; BHI: Not affected";
- else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_HW))
+ else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_HW))
return "; BHI: BHI_DIS_S";
- else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP))
+ 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) && rrsba_disabled)
+ else if (boot_cpu_has(X86_FEATURE_RETPOLINE) &&
+ !boot_cpu_has(X86_FEATURE_RETPOLINE_LFENCE) &&
+ rrsba_disabled)
return "; BHI: Retpoline";
else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT))
return "; BHI: Vulnerable, KVM: SW loop";
--
2.43.0