From: Johannes Wikner Date: Tue, 8 Oct 2024 10:36:30 +0000 (+0200) Subject: x86/bugs: Skip RSB fill at VMEXIT X-Git-Tag: v5.10.228~33 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=e7c0f8ca3bddef44aaab2aafc22c64d0e0f66165;p=thirdparty%2Fkernel%2Fstable.git x86/bugs: Skip RSB fill at VMEXIT commit 0fad2878642ec46225af2054564932745ac5c765 upstream. entry_ibpb() is designed to follow Intel's IBPB specification regardless of CPU. This includes invalidating RSB entries. Hence, if IBPB on VMEXIT has been selected, entry_ibpb() as part of the RET untraining in the VMEXIT path will take care of all BTB and RSB clearing so there's no need to explicitly fill the RSB anymore. [ bp: Massage commit message. ] Suggested-by: Borislav Petkov Signed-off-by: Johannes Wikner Cc: Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index d6e14190cf80d..23f884a5d12c8 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1062,6 +1062,14 @@ do_cmd_auto: case RETBLEED_MITIGATION_IBPB: setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB); mitigate_smt = true; + + /* + * There is no need for RSB filling: entry_ibpb() ensures + * all predictions, including the RSB, are invalidated, + * regardless of IBPB implementation. + */ + setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT); + break; default: @@ -2465,6 +2473,13 @@ static void __init srso_select_mitigation(void) if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) { setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT); srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT; + + /* + * There is no need for RSB filling: entry_ibpb() ensures + * all predictions, including the RSB, are invalidated, + * regardless of IBPB implementation. + */ + setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT); } } else { pr_err("WARNING: kernel not compiled with CPU_SRSO.\n");