From: David Kaplan Date: Fri, 18 Apr 2025 16:17:16 +0000 (-0500) Subject: x86/bugs: Restructure spectre_v2_user mitigation X-Git-Tag: v6.16-rc1~195^2~31^2~5 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=ddfca9430a617780c8ad9691bf44660ae49e2a35;p=thirdparty%2Fkernel%2Flinux.git x86/bugs: Restructure spectre_v2_user mitigation Restructure spectre_v2_user to use select/update/apply functions to create consistent vulnerability handling. The IBPB/STIBP choices are first decided based on the spectre_v2_user command line but can be modified by the spectre_v2 command line option as well. Signed-off-by: David Kaplan Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Josh Poimboeuf Link: https://lore.kernel.org/20250418161721.1855190-12-david.kaplan@amd.com --- diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 207a472d1a6e6..dc75195760ca5 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -60,6 +60,8 @@ static void __init retbleed_select_mitigation(void); static void __init retbleed_update_mitigation(void); static void __init retbleed_apply_mitigation(void); static void __init spectre_v2_user_select_mitigation(void); +static void __init spectre_v2_user_update_mitigation(void); +static void __init spectre_v2_user_apply_mitigation(void); static void __init ssb_select_mitigation(void); static void __init l1tf_select_mitigation(void); static void __init mds_select_mitigation(void); @@ -190,11 +192,6 @@ void __init cpu_select_mitigations(void) spectre_v1_select_mitigation(); spectre_v2_select_mitigation(); retbleed_select_mitigation(); - /* - * spectre_v2_user_select_mitigation() relies on the state set by - * retbleed_select_mitigation(); specifically the STIBP selection is - * forced for UNRET or IBPB. - */ spectre_v2_user_select_mitigation(); ssb_select_mitigation(); l1tf_select_mitigation(); @@ -217,6 +214,13 @@ void __init cpu_select_mitigations(void) * choices. */ retbleed_update_mitigation(); + + /* + * spectre_v2_user_update_mitigation() depends on + * retbleed_update_mitigation(), specifically the STIBP + * selection is forced for UNRET or IBPB. + */ + spectre_v2_user_update_mitigation(); mds_update_mitigation(); taa_update_mitigation(); mmio_update_mitigation(); @@ -224,6 +228,7 @@ void __init cpu_select_mitigations(void) spectre_v1_apply_mitigation(); retbleed_apply_mitigation(); + spectre_v2_user_apply_mitigation(); mds_apply_mitigation(); taa_apply_mitigation(); mmio_apply_mitigation(); @@ -1379,6 +1384,8 @@ enum spectre_v2_mitigation_cmd { SPECTRE_V2_CMD_IBRS, }; +static enum spectre_v2_mitigation_cmd spectre_v2_cmd __ro_after_init = SPECTRE_V2_CMD_AUTO; + enum spectre_v2_user_cmd { SPECTRE_V2_USER_CMD_NONE, SPECTRE_V2_USER_CMD_AUTO, @@ -1417,31 +1424,18 @@ static void __init spec_v2_user_print_cond(const char *reason, bool secure) pr_info("spectre_v2_user=%s forced on command line.\n", reason); } -static __ro_after_init enum spectre_v2_mitigation_cmd spectre_v2_cmd; - -static enum spectre_v2_user_cmd __init -spectre_v2_parse_user_cmdline(void) +static enum spectre_v2_user_cmd __init spectre_v2_parse_user_cmdline(void) { - enum spectre_v2_user_cmd mode; char arg[20]; int ret, i; - mode = IS_ENABLED(CONFIG_MITIGATION_SPECTRE_V2) ? - SPECTRE_V2_USER_CMD_AUTO : SPECTRE_V2_USER_CMD_NONE; - - switch (spectre_v2_cmd) { - case SPECTRE_V2_CMD_NONE: + if (cpu_mitigations_off() || !IS_ENABLED(CONFIG_MITIGATION_SPECTRE_V2)) return SPECTRE_V2_USER_CMD_NONE; - case SPECTRE_V2_CMD_FORCE: - return SPECTRE_V2_USER_CMD_FORCE; - default: - break; - } ret = cmdline_find_option(boot_command_line, "spectre_v2_user", arg, sizeof(arg)); if (ret < 0) - return mode; + return SPECTRE_V2_USER_CMD_AUTO; for (i = 0; i < ARRAY_SIZE(v2_user_options); i++) { if (match_option(arg, ret, v2_user_options[i].option)) { @@ -1452,7 +1446,7 @@ spectre_v2_parse_user_cmdline(void) } pr_err("Unknown user space protection option (%s). Switching to default\n", arg); - return mode; + return SPECTRE_V2_USER_CMD_AUTO; } static inline bool spectre_v2_in_ibrs_mode(enum spectre_v2_mitigation mode) @@ -1460,60 +1454,72 @@ static inline bool spectre_v2_in_ibrs_mode(enum spectre_v2_mitigation mode) return spectre_v2_in_eibrs_mode(mode) || mode == SPECTRE_V2_IBRS; } -static void __init -spectre_v2_user_select_mitigation(void) +static void __init spectre_v2_user_select_mitigation(void) { - enum spectre_v2_user_mitigation mode = SPECTRE_V2_USER_NONE; - enum spectre_v2_user_cmd cmd; - if (!boot_cpu_has(X86_FEATURE_IBPB) && !boot_cpu_has(X86_FEATURE_STIBP)) return; - cmd = spectre_v2_parse_user_cmdline(); - switch (cmd) { + switch (spectre_v2_parse_user_cmdline()) { case SPECTRE_V2_USER_CMD_NONE: - goto set_mode; + return; case SPECTRE_V2_USER_CMD_FORCE: - mode = SPECTRE_V2_USER_STRICT; + spectre_v2_user_ibpb = SPECTRE_V2_USER_STRICT; + spectre_v2_user_stibp = SPECTRE_V2_USER_STRICT; break; case SPECTRE_V2_USER_CMD_AUTO: case SPECTRE_V2_USER_CMD_PRCTL: + spectre_v2_user_ibpb = SPECTRE_V2_USER_PRCTL; + spectre_v2_user_stibp = SPECTRE_V2_USER_PRCTL; + break; case SPECTRE_V2_USER_CMD_PRCTL_IBPB: - mode = SPECTRE_V2_USER_PRCTL; + spectre_v2_user_ibpb = SPECTRE_V2_USER_STRICT; + spectre_v2_user_stibp = SPECTRE_V2_USER_PRCTL; break; case SPECTRE_V2_USER_CMD_SECCOMP: + if (IS_ENABLED(CONFIG_SECCOMP)) + spectre_v2_user_ibpb = SPECTRE_V2_USER_SECCOMP; + else + spectre_v2_user_ibpb = SPECTRE_V2_USER_PRCTL; + spectre_v2_user_stibp = spectre_v2_user_ibpb; + break; case SPECTRE_V2_USER_CMD_SECCOMP_IBPB: + spectre_v2_user_ibpb = SPECTRE_V2_USER_STRICT; if (IS_ENABLED(CONFIG_SECCOMP)) - mode = SPECTRE_V2_USER_SECCOMP; + spectre_v2_user_stibp = SPECTRE_V2_USER_SECCOMP; else - mode = SPECTRE_V2_USER_PRCTL; + spectre_v2_user_stibp = SPECTRE_V2_USER_PRCTL; break; } - /* Initialize Indirect Branch Prediction Barrier */ - if (boot_cpu_has(X86_FEATURE_IBPB)) { - static_branch_enable(&switch_vcpu_ibpb); + /* + * At this point, an STIBP mode other than "off" has been set. + * If STIBP support is not being forced, check if STIBP always-on + * is preferred. + */ + if ((spectre_v2_user_stibp == SPECTRE_V2_USER_PRCTL || + spectre_v2_user_stibp == SPECTRE_V2_USER_SECCOMP) && + boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON)) + spectre_v2_user_stibp = SPECTRE_V2_USER_STRICT_PREFERRED; - spectre_v2_user_ibpb = mode; - switch (cmd) { - case SPECTRE_V2_USER_CMD_NONE: - break; - case SPECTRE_V2_USER_CMD_FORCE: - case SPECTRE_V2_USER_CMD_PRCTL_IBPB: - case SPECTRE_V2_USER_CMD_SECCOMP_IBPB: - static_branch_enable(&switch_mm_always_ibpb); - spectre_v2_user_ibpb = SPECTRE_V2_USER_STRICT; - break; - case SPECTRE_V2_USER_CMD_PRCTL: - case SPECTRE_V2_USER_CMD_AUTO: - case SPECTRE_V2_USER_CMD_SECCOMP: - static_branch_enable(&switch_mm_cond_ibpb); - break; - } + if (!boot_cpu_has(X86_FEATURE_IBPB)) + spectre_v2_user_ibpb = SPECTRE_V2_USER_NONE; - pr_info("mitigation: Enabling %s Indirect Branch Prediction Barrier\n", - static_key_enabled(&switch_mm_always_ibpb) ? - "always-on" : "conditional"); + if (!boot_cpu_has(X86_FEATURE_STIBP)) + spectre_v2_user_stibp = SPECTRE_V2_USER_NONE; +} + +static void __init spectre_v2_user_update_mitigation(void) +{ + if (!boot_cpu_has(X86_FEATURE_IBPB) && !boot_cpu_has(X86_FEATURE_STIBP)) + return; + + /* The spectre_v2 cmd line can override spectre_v2_user options */ + if (spectre_v2_cmd == SPECTRE_V2_CMD_NONE) { + spectre_v2_user_ibpb = SPECTRE_V2_USER_NONE; + spectre_v2_user_stibp = SPECTRE_V2_USER_NONE; + } else if (spectre_v2_cmd == SPECTRE_V2_CMD_FORCE) { + spectre_v2_user_ibpb = SPECTRE_V2_USER_STRICT; + spectre_v2_user_stibp = SPECTRE_V2_USER_STRICT; } /* @@ -1531,30 +1537,44 @@ spectre_v2_user_select_mitigation(void) if (!boot_cpu_has(X86_FEATURE_STIBP) || !cpu_smt_possible() || (spectre_v2_in_eibrs_mode(spectre_v2_enabled) && - !boot_cpu_has(X86_FEATURE_AUTOIBRS))) + !boot_cpu_has(X86_FEATURE_AUTOIBRS))) { + spectre_v2_user_stibp = SPECTRE_V2_USER_NONE; return; + } - /* - * At this point, an STIBP mode other than "off" has been set. - * If STIBP support is not being forced, check if STIBP always-on - * is preferred. - */ - if (mode != SPECTRE_V2_USER_STRICT && - boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON)) - mode = SPECTRE_V2_USER_STRICT_PREFERRED; - - if (retbleed_mitigation == RETBLEED_MITIGATION_UNRET || - retbleed_mitigation == RETBLEED_MITIGATION_IBPB) { - if (mode != SPECTRE_V2_USER_STRICT && - mode != SPECTRE_V2_USER_STRICT_PREFERRED) + if (spectre_v2_user_stibp != SPECTRE_V2_USER_NONE && + (retbleed_mitigation == RETBLEED_MITIGATION_UNRET || + retbleed_mitigation == RETBLEED_MITIGATION_IBPB)) { + if (spectre_v2_user_stibp != SPECTRE_V2_USER_STRICT && + spectre_v2_user_stibp != SPECTRE_V2_USER_STRICT_PREFERRED) pr_info("Selecting STIBP always-on mode to complement retbleed mitigation\n"); - mode = SPECTRE_V2_USER_STRICT_PREFERRED; + spectre_v2_user_stibp = SPECTRE_V2_USER_STRICT_PREFERRED; } + pr_info("%s\n", spectre_v2_user_strings[spectre_v2_user_stibp]); +} - spectre_v2_user_stibp = mode; +static void __init spectre_v2_user_apply_mitigation(void) +{ + /* Initialize Indirect Branch Prediction Barrier */ + if (spectre_v2_user_ibpb != SPECTRE_V2_USER_NONE) { + static_branch_enable(&switch_vcpu_ibpb); + + switch (spectre_v2_user_ibpb) { + case SPECTRE_V2_USER_STRICT: + static_branch_enable(&switch_mm_always_ibpb); + break; + case SPECTRE_V2_USER_PRCTL: + case SPECTRE_V2_USER_SECCOMP: + static_branch_enable(&switch_mm_cond_ibpb); + break; + default: + break; + } -set_mode: - pr_info("%s\n", spectre_v2_user_strings[mode]); + pr_info("mitigation: Enabling %s Indirect Branch Prediction Barrier\n", + static_key_enabled(&switch_mm_always_ibpb) ? + "always-on" : "conditional"); + } } static const char * const spectre_v2_strings[] = {