From 0fad2878642ec46225af2054564932745ac5c765 Mon Sep 17 00:00:00 2001 From: Johannes Wikner Date: Tue, 8 Oct 2024 12:36:30 +0200 Subject: x86/bugs: Skip RSB fill at VMEXIT 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: --- arch/x86/kernel/cpu/bugs.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'arch') diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index d1915427b4ff..4474c5a1cd9a 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1117,6 +1117,14 @@ do_cmd_auto: setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB); setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT); 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; case RETBLEED_MITIGATION_STUFF: @@ -2638,6 +2646,13 @@ 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 MITIGATION_SRSO.\n"); -- cgit v1.2.3