From 5a15d8348881e9371afdf9f5357a135489496955 Mon Sep 17 00:00:00 2001 From: "Borislav Petkov (AMD)" Date: Mon, 7 Aug 2023 10:46:04 +0200 Subject: [PATCH] x86/srso: Tie SBPB bit setting to microcode patch detection The SBPB bit in MSR_IA32_PRED_CMD is supported only after a microcode patch has been applied so set X86_FEATURE_SBPB only then. Otherwise, guests would attempt to set that bit and #GP on the MSR write. While at it, make SMT detection more robust as some guests - depending on how and what CPUID leafs their report - lead to cpu_smt_control getting set to CPU_SMT_NOT_SUPPORTED but SRSO_NO should be set for any guest incarnation where one simply cannot do SMT, for whatever reason. Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation") Reported-by: Konrad Rzeszutek Wilk Reported-by: Salvatore Bonaccorso Signed-off-by: Borislav Petkov (AMD) --- arch/x86/kernel/cpu/amd.c | 19 ++++++++++++------- arch/x86/kernel/cpu/bugs.c | 7 +++---- 2 files changed, 15 insertions(+), 11 deletions(-) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index 834f310..41e10c2 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -1238,14 +1238,19 @@ EXPORT_SYMBOL_GPL(amd_get_highest_perf); bool cpu_has_ibpb_brtype_microcode(void) { - u8 fam = boot_cpu_data.x86; - + switch (boot_cpu_data.x86) { /* Zen1/2 IBPB flushes branch type predictions too. */ - if (fam == 0x17) + case 0x17: return boot_cpu_has(X86_FEATURE_AMD_IBPB); - /* Poke the MSR bit on Zen3/4 to check its presence. */ - else if (fam == 0x19) - return !wrmsrl_safe(MSR_IA32_PRED_CMD, PRED_CMD_SBPB); - else + case 0x19: + /* Poke the MSR bit on Zen3/4 to check its presence. */ + if (!wrmsrl_safe(MSR_IA32_PRED_CMD, PRED_CMD_SBPB)) { + setup_force_cpu_cap(X86_FEATURE_SBPB); + return true; + } else { + return false; + } + default: return false; + } } diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 7314a6b..2afe69b 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -2265,14 +2265,13 @@ static void __init srso_select_mitigation(void) * flags for guests. */ setup_force_cpu_cap(X86_FEATURE_IBPB_BRTYPE); - setup_force_cpu_cap(X86_FEATURE_SBPB); /* * Zen1/2 with SMT off aren't vulnerable after the right * IBPB microcode has been applied. */ if ((boot_cpu_data.x86 < 0x19) && - (cpu_smt_control == CPU_SMT_DISABLED)) + (!cpu_smt_possible() || (cpu_smt_control == CPU_SMT_DISABLED))) setup_force_cpu_cap(X86_FEATURE_SRSO_NO); } @@ -2345,8 +2344,8 @@ static void __init srso_select_mitigation(void) pr_info("%s%s\n", srso_strings[srso_mitigation], (has_microcode ? "" : ", no microcode")); pred_cmd: - if (boot_cpu_has(X86_FEATURE_SRSO_NO) || - srso_cmd == SRSO_CMD_OFF) + if ((boot_cpu_has(X86_FEATURE_SRSO_NO) || srso_cmd == SRSO_CMD_OFF) && + boot_cpu_has(X86_FEATURE_SBPB)) x86_pred_cmd = PRED_CMD_SBPB; } -- 2.7.4