From 1f4bb068b498a544ae913764a797449463ef620c Mon Sep 17 00:00:00 2001 From: David Kaplan Date: Fri, 18 Apr 2025 11:17:21 -0500 Subject: [PATCH] x86/bugs: Restructure SRSO mitigation Restructure SRSO to use select/update/apply functions to create consistent vulnerability handling. Like with retbleed, the command line options directly select mitigations which can later be modified. While at it, remove a comment which doesn't apply anymore due to the changed mitigation detection flow. Signed-off-by: David Kaplan Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Josh Poimboeuf Link: https://lore.kernel.org/20250418161721.1855190-17-david.kaplan@amd.com --- arch/x86/kernel/cpu/bugs.c | 215 +++++++++++++++++-------------------- 1 file changed, 101 insertions(+), 114 deletions(-) diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 25d84e2a4f2ba..a4f3b1d034062 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -84,6 +84,8 @@ static void __init srbds_select_mitigation(void); static void __init srbds_apply_mitigation(void); static void __init l1d_flush_select_mitigation(void); static void __init srso_select_mitigation(void); +static void __init srso_update_mitigation(void); +static void __init srso_apply_mitigation(void); static void __init gds_select_mitigation(void); static void __init gds_apply_mitigation(void); static void __init bhi_select_mitigation(void); @@ -208,11 +210,6 @@ void __init cpu_select_mitigations(void) rfds_select_mitigation(); srbds_select_mitigation(); l1d_flush_select_mitigation(); - - /* - * srso_select_mitigation() depends and must run after - * retbleed_select_mitigation(). - */ srso_select_mitigation(); gds_select_mitigation(); bhi_select_mitigation(); @@ -240,6 +237,8 @@ void __init cpu_select_mitigations(void) mmio_update_mitigation(); rfds_update_mitigation(); bhi_update_mitigation(); + /* srso_update_mitigation() depends on retbleed_update_mitigation(). */ + srso_update_mitigation(); spectre_v1_apply_mitigation(); spectre_v2_apply_mitigation(); @@ -252,6 +251,7 @@ void __init cpu_select_mitigations(void) mmio_apply_mitigation(); rfds_apply_mitigation(); srbds_apply_mitigation(); + srso_apply_mitigation(); gds_apply_mitigation(); bhi_apply_mitigation(); } @@ -2674,6 +2674,7 @@ early_param("l1tf", l1tf_cmdline); enum srso_mitigation { SRSO_MITIGATION_NONE, + SRSO_MITIGATION_AUTO, SRSO_MITIGATION_UCODE_NEEDED, SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED, SRSO_MITIGATION_MICROCODE, @@ -2683,14 +2684,6 @@ enum srso_mitigation { SRSO_MITIGATION_BP_SPEC_REDUCE, }; -enum srso_mitigation_cmd { - SRSO_CMD_OFF, - SRSO_CMD_MICROCODE, - SRSO_CMD_SAFE_RET, - SRSO_CMD_IBPB, - SRSO_CMD_IBPB_ON_VMEXIT, -}; - static const char * const srso_strings[] = { [SRSO_MITIGATION_NONE] = "Vulnerable", [SRSO_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode", @@ -2702,8 +2695,7 @@ static const char * const srso_strings[] = { [SRSO_MITIGATION_BP_SPEC_REDUCE] = "Mitigation: Reduced Speculation" }; -static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_NONE; -static enum srso_mitigation_cmd srso_cmd __ro_after_init = SRSO_CMD_SAFE_RET; +static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_AUTO; static int __init srso_parse_cmdline(char *str) { @@ -2711,15 +2703,15 @@ static int __init srso_parse_cmdline(char *str) return -EINVAL; if (!strcmp(str, "off")) - srso_cmd = SRSO_CMD_OFF; + srso_mitigation = SRSO_MITIGATION_NONE; else if (!strcmp(str, "microcode")) - srso_cmd = SRSO_CMD_MICROCODE; + srso_mitigation = SRSO_MITIGATION_MICROCODE; else if (!strcmp(str, "safe-ret")) - srso_cmd = SRSO_CMD_SAFE_RET; + srso_mitigation = SRSO_MITIGATION_SAFE_RET; else if (!strcmp(str, "ibpb")) - srso_cmd = SRSO_CMD_IBPB; + srso_mitigation = SRSO_MITIGATION_IBPB; else if (!strcmp(str, "ibpb-vmexit")) - srso_cmd = SRSO_CMD_IBPB_ON_VMEXIT; + srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT; else pr_err("Ignoring unknown SRSO option (%s).", str); @@ -2731,132 +2723,83 @@ early_param("spec_rstack_overflow", srso_parse_cmdline); static void __init srso_select_mitigation(void) { - bool has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE); + bool has_microcode; - if (!boot_cpu_has_bug(X86_BUG_SRSO) || - cpu_mitigations_off() || - srso_cmd == SRSO_CMD_OFF) { - if (boot_cpu_has(X86_FEATURE_SBPB)) - x86_pred_cmd = PRED_CMD_SBPB; - goto out; - } + if (!boot_cpu_has_bug(X86_BUG_SRSO) || cpu_mitigations_off()) + srso_mitigation = SRSO_MITIGATION_NONE; + if (srso_mitigation == SRSO_MITIGATION_NONE) + return; + + if (srso_mitigation == SRSO_MITIGATION_AUTO) + srso_mitigation = SRSO_MITIGATION_SAFE_RET; + + has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE); if (has_microcode) { /* * Zen1/2 with SMT off aren't vulnerable after the right * IBPB microcode has been applied. - * - * Zen1/2 don't have SBPB, no need to try to enable it here. */ if (boot_cpu_data.x86 < 0x19 && !cpu_smt_possible()) { setup_force_cpu_cap(X86_FEATURE_SRSO_NO); - goto out; - } - - if (retbleed_mitigation == RETBLEED_MITIGATION_IBPB) { - srso_mitigation = SRSO_MITIGATION_IBPB; - goto out; + srso_mitigation = SRSO_MITIGATION_NONE; + return; } } else { pr_warn("IBPB-extending microcode not applied!\n"); pr_warn(SRSO_NOTICE); - - /* may be overwritten by SRSO_CMD_SAFE_RET below */ - srso_mitigation = SRSO_MITIGATION_UCODE_NEEDED; } - switch (srso_cmd) { - case SRSO_CMD_MICROCODE: - if (has_microcode) { - srso_mitigation = SRSO_MITIGATION_MICROCODE; - pr_warn(SRSO_NOTICE); - } - break; - - case SRSO_CMD_SAFE_RET: - if (boot_cpu_has(X86_FEATURE_SRSO_USER_KERNEL_NO)) + switch (srso_mitigation) { + case SRSO_MITIGATION_SAFE_RET: + if (boot_cpu_has(X86_FEATURE_SRSO_USER_KERNEL_NO)) { + srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT; goto ibpb_on_vmexit; + } - if (IS_ENABLED(CONFIG_MITIGATION_SRSO)) { - /* - * Enable the return thunk for generated code - * like ftrace, static_call, etc. - */ - setup_force_cpu_cap(X86_FEATURE_RETHUNK); - setup_force_cpu_cap(X86_FEATURE_UNRET); - - if (boot_cpu_data.x86 == 0x19) { - setup_force_cpu_cap(X86_FEATURE_SRSO_ALIAS); - x86_return_thunk = srso_alias_return_thunk; - } else { - setup_force_cpu_cap(X86_FEATURE_SRSO); - x86_return_thunk = srso_return_thunk; - } - if (has_microcode) - srso_mitigation = SRSO_MITIGATION_SAFE_RET; - else - srso_mitigation = SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED; - } else { + if (!IS_ENABLED(CONFIG_MITIGATION_SRSO)) { pr_err("WARNING: kernel not compiled with MITIGATION_SRSO.\n"); + srso_mitigation = SRSO_MITIGATION_NONE; } - break; - case SRSO_CMD_IBPB: - if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY)) { - if (has_microcode) { - setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB); - setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT); - srso_mitigation = SRSO_MITIGATION_IBPB; - - /* - * IBPB on entry already obviates the need for - * software-based untraining so clear those in case some - * other mitigation like Retbleed has selected them. - */ - setup_clear_cpu_cap(X86_FEATURE_UNRET); - setup_clear_cpu_cap(X86_FEATURE_RETHUNK); - - /* - * There is no need for RSB filling: write_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_IBPB_ENTRY.\n"); - } + if (!has_microcode) + srso_mitigation = SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED; break; - ibpb_on_vmexit: - case SRSO_CMD_IBPB_ON_VMEXIT: + case SRSO_MITIGATION_IBPB_ON_VMEXIT: if (boot_cpu_has(X86_FEATURE_SRSO_BP_SPEC_REDUCE)) { pr_notice("Reducing speculation to address VM/HV SRSO attack vector.\n"); srso_mitigation = SRSO_MITIGATION_BP_SPEC_REDUCE; break; } - - if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY)) { - if (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: write_ibpb() ensures - * all predictions, including the RSB, are invalidated, - * regardless of IBPB implementation. - */ - setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT); - } - } else { + fallthrough; + case SRSO_MITIGATION_IBPB: + if (!IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY)) { pr_err("WARNING: kernel not compiled with MITIGATION_IBPB_ENTRY.\n"); + srso_mitigation = SRSO_MITIGATION_NONE; } + + if (!has_microcode) + srso_mitigation = SRSO_MITIGATION_UCODE_NEEDED; break; default: break; } +} -out: +static void __init srso_update_mitigation(void) +{ + /* If retbleed is using IBPB, that works for SRSO as well */ + if (retbleed_mitigation == RETBLEED_MITIGATION_IBPB && + boot_cpu_has(X86_FEATURE_IBPB_BRTYPE)) + srso_mitigation = SRSO_MITIGATION_IBPB; + + if (boot_cpu_has_bug(X86_BUG_SRSO) && !cpu_mitigations_off()) + pr_info("%s\n", srso_strings[srso_mitigation]); +} + +static void __init srso_apply_mitigation(void) +{ /* * Clear the feature flag if this mitigation is not selected as that * feature flag controls the BpSpecReduce MSR bit toggling in KVM. @@ -2864,8 +2807,52 @@ out: if (srso_mitigation != SRSO_MITIGATION_BP_SPEC_REDUCE) setup_clear_cpu_cap(X86_FEATURE_SRSO_BP_SPEC_REDUCE); - if (srso_mitigation != SRSO_MITIGATION_NONE) - pr_info("%s\n", srso_strings[srso_mitigation]); + if (srso_mitigation == SRSO_MITIGATION_NONE) { + if (boot_cpu_has(X86_FEATURE_SBPB)) + x86_pred_cmd = PRED_CMD_SBPB; + return; + } + + switch (srso_mitigation) { + case SRSO_MITIGATION_SAFE_RET: + case SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED: + /* + * Enable the return thunk for generated code + * like ftrace, static_call, etc. + */ + setup_force_cpu_cap(X86_FEATURE_RETHUNK); + setup_force_cpu_cap(X86_FEATURE_UNRET); + + if (boot_cpu_data.x86 == 0x19) { + setup_force_cpu_cap(X86_FEATURE_SRSO_ALIAS); + x86_return_thunk = srso_alias_return_thunk; + } else { + setup_force_cpu_cap(X86_FEATURE_SRSO); + x86_return_thunk = srso_return_thunk; + } + break; + case SRSO_MITIGATION_IBPB: + setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB); + /* + * IBPB on entry already obviates the need for + * software-based untraining so clear those in case some + * other mitigation like Retbleed has selected them. + */ + setup_clear_cpu_cap(X86_FEATURE_UNRET); + setup_clear_cpu_cap(X86_FEATURE_RETHUNK); + fallthrough; + case SRSO_MITIGATION_IBPB_ON_VMEXIT: + setup_force_cpu_cap(X86_FEATURE_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); + break; + default: + break; + } } #undef pr_fmt -- 2.47.2