From 480e803dacf8be92b1104ca65f2be4cb0e191375 Mon Sep 17 00:00:00 2001 From: David Kaplan Date: Fri, 18 Apr 2025 11:17:18 -0500 Subject: [PATCH] x86/bugs: Restructure spectre_v2 mitigation Restructure spectre_v2 to use select/update/apply functions to create consistent vulnerability handling. The spectre_v2 mitigation may be updated based on the selected retbleed mitigation. Signed-off-by: David Kaplan Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Josh Poimboeuf Link: https://lore.kernel.org/20250418161721.1855190-14-david.kaplan@amd.com --- arch/x86/kernel/cpu/bugs.c | 101 ++++++++++++++++++++----------------- 1 file changed, 56 insertions(+), 45 deletions(-) diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 100a320443856..93d07438eea78 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -56,6 +56,8 @@ static void __init spectre_v1_select_mitigation(void); static void __init spectre_v1_apply_mitigation(void); static void __init spectre_v2_select_mitigation(void); +static void __init spectre_v2_update_mitigation(void); +static void __init spectre_v2_apply_mitigation(void); static void __init retbleed_select_mitigation(void); static void __init retbleed_update_mitigation(void); static void __init retbleed_apply_mitigation(void); @@ -217,6 +219,12 @@ void __init cpu_select_mitigations(void) * After mitigations are selected, some may need to update their * choices. */ + spectre_v2_update_mitigation(); + /* + * retbleed_update_mitigation() relies on the state set by + * spectre_v2_update_mitigation(); specifically it wants to know about + * spectre_v2=ibrs. + */ retbleed_update_mitigation(); /* @@ -232,6 +240,7 @@ void __init cpu_select_mitigations(void) bhi_update_mitigation(); spectre_v1_apply_mitigation(); + spectre_v2_apply_mitigation(); retbleed_apply_mitigation(); spectre_v2_user_apply_mitigation(); mds_apply_mitigation(); @@ -1878,75 +1887,80 @@ static void __init bhi_apply_mitigation(void) static void __init spectre_v2_select_mitigation(void) { - enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline(); - enum spectre_v2_mitigation mode = SPECTRE_V2_NONE; + spectre_v2_cmd = spectre_v2_parse_cmdline(); - /* - * If the CPU is not affected and the command line mode is NONE or AUTO - * then nothing to do. - */ if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2) && - (cmd == SPECTRE_V2_CMD_NONE || cmd == SPECTRE_V2_CMD_AUTO)) + (spectre_v2_cmd == SPECTRE_V2_CMD_NONE || spectre_v2_cmd == SPECTRE_V2_CMD_AUTO)) return; - switch (cmd) { + switch (spectre_v2_cmd) { case SPECTRE_V2_CMD_NONE: return; case SPECTRE_V2_CMD_FORCE: case SPECTRE_V2_CMD_AUTO: if (boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) { - mode = SPECTRE_V2_EIBRS; - break; - } - - if (IS_ENABLED(CONFIG_MITIGATION_IBRS_ENTRY) && - boot_cpu_has_bug(X86_BUG_RETBLEED) && - retbleed_mitigation != RETBLEED_MITIGATION_NONE && - retbleed_mitigation != RETBLEED_MITIGATION_STUFF && - boot_cpu_has(X86_FEATURE_IBRS) && - boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) { - mode = SPECTRE_V2_IBRS; + spectre_v2_enabled = SPECTRE_V2_EIBRS; break; } - mode = spectre_v2_select_retpoline(); + spectre_v2_enabled = spectre_v2_select_retpoline(); break; case SPECTRE_V2_CMD_RETPOLINE_LFENCE: pr_err(SPECTRE_V2_LFENCE_MSG); - mode = SPECTRE_V2_LFENCE; + spectre_v2_enabled = SPECTRE_V2_LFENCE; break; case SPECTRE_V2_CMD_RETPOLINE_GENERIC: - mode = SPECTRE_V2_RETPOLINE; + spectre_v2_enabled = SPECTRE_V2_RETPOLINE; break; case SPECTRE_V2_CMD_RETPOLINE: - mode = spectre_v2_select_retpoline(); + spectre_v2_enabled = spectre_v2_select_retpoline(); break; case SPECTRE_V2_CMD_IBRS: - mode = SPECTRE_V2_IBRS; + spectre_v2_enabled = SPECTRE_V2_IBRS; break; case SPECTRE_V2_CMD_EIBRS: - mode = SPECTRE_V2_EIBRS; + spectre_v2_enabled = SPECTRE_V2_EIBRS; break; case SPECTRE_V2_CMD_EIBRS_LFENCE: - mode = SPECTRE_V2_EIBRS_LFENCE; + spectre_v2_enabled = SPECTRE_V2_EIBRS_LFENCE; break; case SPECTRE_V2_CMD_EIBRS_RETPOLINE: - mode = SPECTRE_V2_EIBRS_RETPOLINE; + spectre_v2_enabled = SPECTRE_V2_EIBRS_RETPOLINE; break; } +} - if (mode == SPECTRE_V2_EIBRS && unprivileged_ebpf_enabled()) +static void __init spectre_v2_update_mitigation(void) +{ + if (spectre_v2_cmd == SPECTRE_V2_CMD_AUTO) { + if (IS_ENABLED(CONFIG_MITIGATION_IBRS_ENTRY) && + boot_cpu_has_bug(X86_BUG_RETBLEED) && + retbleed_mitigation != RETBLEED_MITIGATION_NONE && + retbleed_mitigation != RETBLEED_MITIGATION_STUFF && + boot_cpu_has(X86_FEATURE_IBRS) && + boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) { + spectre_v2_enabled = SPECTRE_V2_IBRS; + } + } + + if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2) && !cpu_mitigations_off()) + pr_info("%s\n", spectre_v2_strings[spectre_v2_enabled]); +} + +static void __init spectre_v2_apply_mitigation(void) +{ + if (spectre_v2_enabled == SPECTRE_V2_EIBRS && unprivileged_ebpf_enabled()) pr_err(SPECTRE_V2_EIBRS_EBPF_MSG); - if (spectre_v2_in_ibrs_mode(mode)) { + if (spectre_v2_in_ibrs_mode(spectre_v2_enabled)) { if (boot_cpu_has(X86_FEATURE_AUTOIBRS)) { msr_set_bit(MSR_EFER, _EFER_AUTOIBRS); } else { @@ -1955,8 +1969,10 @@ static void __init spectre_v2_select_mitigation(void) } } - switch (mode) { + switch (spectre_v2_enabled) { case SPECTRE_V2_NONE: + return; + case SPECTRE_V2_EIBRS: break; @@ -1982,15 +1998,12 @@ static void __init spectre_v2_select_mitigation(void) * JMPs gets protection against BHI and Intramode-BTI, but RET * prediction from a non-RSB predictor is still a risk. */ - if (mode == SPECTRE_V2_EIBRS_LFENCE || - mode == SPECTRE_V2_EIBRS_RETPOLINE || - mode == SPECTRE_V2_RETPOLINE) + if (spectre_v2_enabled == SPECTRE_V2_EIBRS_LFENCE || + spectre_v2_enabled == SPECTRE_V2_EIBRS_RETPOLINE || + spectre_v2_enabled == SPECTRE_V2_RETPOLINE) spec_ctrl_disable_kernel_rrsba(); - spectre_v2_enabled = mode; - pr_info("%s\n", spectre_v2_strings[mode]); - - spectre_v2_select_rsb_mitigation(mode); + spectre_v2_select_rsb_mitigation(spectre_v2_enabled); /* * Retpoline protects the kernel, but doesn't protect firmware. IBRS @@ -1998,10 +2011,10 @@ static void __init spectre_v2_select_mitigation(void) * firmware calls only when IBRS / Enhanced / Automatic IBRS aren't * otherwise enabled. * - * Use "mode" to check Enhanced IBRS instead of boot_cpu_has(), because - * the user might select retpoline on the kernel command line and if - * the CPU supports Enhanced IBRS, kernel might un-intentionally not - * enable IBRS around firmware calls. + * Use "spectre_v2_enabled" to check Enhanced IBRS instead of + * boot_cpu_has(), because the user might select retpoline on the kernel + * command line and if the CPU supports Enhanced IBRS, kernel might + * un-intentionally not enable IBRS around firmware calls. */ if (boot_cpu_has_bug(X86_BUG_RETBLEED) && boot_cpu_has(X86_FEATURE_IBPB) && @@ -2013,13 +2026,11 @@ static void __init spectre_v2_select_mitigation(void) pr_info("Enabling Speculation Barrier for firmware calls\n"); } - } else if (boot_cpu_has(X86_FEATURE_IBRS) && !spectre_v2_in_ibrs_mode(mode)) { + } else if (boot_cpu_has(X86_FEATURE_IBRS) && + !spectre_v2_in_ibrs_mode(spectre_v2_enabled)) { setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW); pr_info("Enabling Restricted Speculation for firmware calls\n"); } - - /* Set up IBPB and STIBP depending on the general spectre V2 command */ - spectre_v2_cmd = cmd; } static void update_stibp_msr(void * __unused) -- 2.47.2