From 98ff5c071d1cde9426b0bfa449c43d49ec58f1c4 Mon Sep 17 00:00:00 2001 From: Pawan Gupta Date: Wed, 11 Jun 2025 10:29:00 -0700 Subject: [PATCH] x86/bugs: Avoid AUTO after the select step in the retbleed mitigation The retbleed select function leaves the mitigation to AUTO in some cases. Moreover, the update function can also set the mitigation to AUTO. This is inconsistent with other mitigations and requires explicit handling of AUTO at the end of update step. Make sure a mitigation gets selected in the select step, and do not change it to AUTO in the update step. When no mitigation can be selected leave it to NONE, which is what AUTO was getting changed to in the end. Suggested-by: Borislav Petkov Signed-off-by: Pawan Gupta Signed-off-by: Borislav Petkov (AMD) Acked-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/20250611-eibrs-fix-v4-1-5ff86cac6c61@linux.intel.com --- arch/x86/kernel/cpu/bugs.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 7f94e6a5497d..53649df2c4d6 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1247,6 +1247,14 @@ static void __init retbleed_select_mitigation(void) retbleed_mitigation = RETBLEED_MITIGATION_IBPB; else retbleed_mitigation = RETBLEED_MITIGATION_NONE; + } else if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) { + /* Final mitigation depends on spectre-v2 selection */ + if (boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) + retbleed_mitigation = RETBLEED_MITIGATION_EIBRS; + else if (boot_cpu_has(X86_FEATURE_IBRS)) + retbleed_mitigation = RETBLEED_MITIGATION_IBRS; + else + retbleed_mitigation = RETBLEED_MITIGATION_NONE; } } @@ -1255,9 +1263,6 @@ static void __init retbleed_update_mitigation(void) if (!boot_cpu_has_bug(X86_BUG_RETBLEED) || cpu_mitigations_off()) return; - if (retbleed_mitigation == RETBLEED_MITIGATION_NONE) - goto out; - /* * retbleed=stuff is only allowed on Intel. If stuffing can't be used * then a different mitigation will be selected below. @@ -1268,7 +1273,7 @@ static void __init retbleed_update_mitigation(void) its_mitigation == ITS_MITIGATION_RETPOLINE_STUFF) { if (spectre_v2_enabled != SPECTRE_V2_RETPOLINE) { pr_err("WARNING: retbleed=stuff depends on spectre_v2=retpoline\n"); - retbleed_mitigation = RETBLEED_MITIGATION_AUTO; + retbleed_mitigation = RETBLEED_MITIGATION_NONE; } else { if (retbleed_mitigation != RETBLEED_MITIGATION_STUFF) pr_info("Retbleed mitigation updated to stuffing\n"); @@ -1294,15 +1299,11 @@ static void __init retbleed_update_mitigation(void) if (retbleed_mitigation != RETBLEED_MITIGATION_STUFF) pr_err(RETBLEED_INTEL_MSG); } - /* If nothing has set the mitigation yet, default to NONE. */ - if (retbleed_mitigation == RETBLEED_MITIGATION_AUTO) - retbleed_mitigation = RETBLEED_MITIGATION_NONE; } -out: + pr_info("%s\n", retbleed_strings[retbleed_mitigation]); } - static void __init retbleed_apply_mitigation(void) { bool mitigate_smt = false; -- 2.51.0