From: Josh Poimboeuf Date: Tue, 8 Apr 2025 21:47:33 +0000 (-0700) Subject: x86/bugs: Don't fill RSB on VMEXIT with eIBRS+retpoline X-Git-Tag: v6.15-rc2~19^2~6 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=18bae0dfec15b24ec14ca17dc18603372f5f254f;p=thirdparty%2Fkernel%2Flinux.git x86/bugs: Don't fill RSB on VMEXIT with eIBRS+retpoline eIBRS protects against guest->host RSB underflow/poisoning attacks. Adding retpoline to the mix doesn't change that. Retpoline has a balanced CALL/RET anyway. So the current full RSB filling on VMEXIT with eIBRS+retpoline is overkill. Disable it or do the VMEXIT_LITE mitigation if needed. Suggested-by: Pawan Gupta Signed-off-by: Josh Poimboeuf Signed-off-by: Ingo Molnar Reviewed-by: Pawan Gupta Reviewed-by: Amit Shah Reviewed-by: Nikolay Borisov Cc: Paolo Bonzini Cc: Vitaly Kuznetsov Cc: Sean Christopherson Cc: David Woodhouse Link: https://lore.kernel.org/r/84a1226e5c9e2698eae1b5ade861f1b8bf3677dc.1744148254.git.jpoimboe@kernel.org --- diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 99265098d0450..a10b37bb747ed 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1617,20 +1617,20 @@ static void __init spectre_v2_determine_rsb_fill_type_at_vmexit(enum spectre_v2_ case SPECTRE_V2_NONE: return; - case SPECTRE_V2_EIBRS_LFENCE: case SPECTRE_V2_EIBRS: + case SPECTRE_V2_EIBRS_LFENCE: + case SPECTRE_V2_EIBRS_RETPOLINE: if (boot_cpu_has_bug(X86_BUG_EIBRS_PBRSB)) { - setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT_LITE); pr_info("Spectre v2 / PBRSB-eIBRS: Retire a single CALL on VMEXIT\n"); + setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT_LITE); } return; - case SPECTRE_V2_EIBRS_RETPOLINE: case SPECTRE_V2_RETPOLINE: case SPECTRE_V2_LFENCE: case SPECTRE_V2_IBRS: - setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT); pr_info("Spectre v2 / SpectreRSB : Filling RSB on VMEXIT\n"); + setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT); return; }