From: David Kaplan Date: Fri, 18 Apr 2025 16:17:15 +0000 (-0500) Subject: x86/bugs: Restructure retbleed mitigation X-Git-Tag: v6.16-rc1~195^2~31^2~6 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e3b78a7ad5ea718ea1dbaeb02ba9a6aa2aee9324;p=thirdparty%2Fkernel%2Flinux.git x86/bugs: Restructure retbleed mitigation Restructure retbleed mitigation to use select/update/apply functions to create consistent vulnerability handling. The retbleed_update_mitigation() simplifies the dependency between spectre_v2 and retbleed. The command line options now directly select a preferred mitigation which simplifies the logic. Signed-off-by: David Kaplan Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Josh Poimboeuf Link: https://lore.kernel.org/20250418161721.1855190-11-david.kaplan@amd.com --- diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 7edf42912cdf8..207a472d1a6e6 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -57,6 +57,8 @@ 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 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 ssb_select_mitigation(void); static void __init l1tf_select_mitigation(void); @@ -187,11 +189,6 @@ void __init cpu_select_mitigations(void) /* Select the proper CPU mitigations before patching alternatives: */ spectre_v1_select_mitigation(); spectre_v2_select_mitigation(); - /* - * retbleed_select_mitigation() relies on the state set by - * spectre_v2_select_mitigation(); specifically it wants to know about - * spectre_v2=ibrs. - */ retbleed_select_mitigation(); /* * spectre_v2_user_select_mitigation() relies on the state set by @@ -219,12 +216,14 @@ void __init cpu_select_mitigations(void) * After mitigations are selected, some may need to update their * choices. */ + retbleed_update_mitigation(); mds_update_mitigation(); taa_update_mitigation(); mmio_update_mitigation(); rfds_update_mitigation(); spectre_v1_apply_mitigation(); + retbleed_apply_mitigation(); mds_apply_mitigation(); taa_apply_mitigation(); mmio_apply_mitigation(); @@ -1085,6 +1084,7 @@ enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init = SPECTRE_V2_NONE; enum retbleed_mitigation { RETBLEED_MITIGATION_NONE, + RETBLEED_MITIGATION_AUTO, RETBLEED_MITIGATION_UNRET, RETBLEED_MITIGATION_IBPB, RETBLEED_MITIGATION_IBRS, @@ -1092,14 +1092,6 @@ enum retbleed_mitigation { RETBLEED_MITIGATION_STUFF, }; -enum retbleed_mitigation_cmd { - RETBLEED_CMD_OFF, - RETBLEED_CMD_AUTO, - RETBLEED_CMD_UNRET, - RETBLEED_CMD_IBPB, - RETBLEED_CMD_STUFF, -}; - static const char * const retbleed_strings[] = { [RETBLEED_MITIGATION_NONE] = "Vulnerable", [RETBLEED_MITIGATION_UNRET] = "Mitigation: untrained return thunk", @@ -1110,9 +1102,7 @@ static const char * const retbleed_strings[] = { }; static enum retbleed_mitigation retbleed_mitigation __ro_after_init = - RETBLEED_MITIGATION_NONE; -static enum retbleed_mitigation_cmd retbleed_cmd __ro_after_init = - IS_ENABLED(CONFIG_MITIGATION_RETBLEED) ? RETBLEED_CMD_AUTO : RETBLEED_CMD_OFF; + IS_ENABLED(CONFIG_MITIGATION_RETBLEED) ? RETBLEED_MITIGATION_AUTO : RETBLEED_MITIGATION_NONE; static int __ro_after_init retbleed_nosmt = false; @@ -1129,15 +1119,15 @@ static int __init retbleed_parse_cmdline(char *str) } if (!strcmp(str, "off")) { - retbleed_cmd = RETBLEED_CMD_OFF; + retbleed_mitigation = RETBLEED_MITIGATION_NONE; } else if (!strcmp(str, "auto")) { - retbleed_cmd = RETBLEED_CMD_AUTO; + retbleed_mitigation = RETBLEED_MITIGATION_AUTO; } else if (!strcmp(str, "unret")) { - retbleed_cmd = RETBLEED_CMD_UNRET; + retbleed_mitigation = RETBLEED_MITIGATION_UNRET; } else if (!strcmp(str, "ibpb")) { - retbleed_cmd = RETBLEED_CMD_IBPB; + retbleed_mitigation = RETBLEED_MITIGATION_IBPB; } else if (!strcmp(str, "stuff")) { - retbleed_cmd = RETBLEED_CMD_STUFF; + retbleed_mitigation = RETBLEED_MITIGATION_STUFF; } else if (!strcmp(str, "nosmt")) { retbleed_nosmt = true; } else if (!strcmp(str, "force")) { @@ -1158,76 +1148,109 @@ early_param("retbleed", retbleed_parse_cmdline); static void __init retbleed_select_mitigation(void) { - bool mitigate_smt = false; - - if (!boot_cpu_has_bug(X86_BUG_RETBLEED) || cpu_mitigations_off()) - return; - - switch (retbleed_cmd) { - case RETBLEED_CMD_OFF: + if (!boot_cpu_has_bug(X86_BUG_RETBLEED) || cpu_mitigations_off()) { + retbleed_mitigation = RETBLEED_MITIGATION_NONE; return; + } - case RETBLEED_CMD_UNRET: - if (IS_ENABLED(CONFIG_MITIGATION_UNRET_ENTRY)) { - retbleed_mitigation = RETBLEED_MITIGATION_UNRET; - } else { + switch (retbleed_mitigation) { + case RETBLEED_MITIGATION_UNRET: + if (!IS_ENABLED(CONFIG_MITIGATION_UNRET_ENTRY)) { + retbleed_mitigation = RETBLEED_MITIGATION_AUTO; pr_err("WARNING: kernel not compiled with MITIGATION_UNRET_ENTRY.\n"); - goto do_cmd_auto; } break; - - case RETBLEED_CMD_IBPB: + case RETBLEED_MITIGATION_IBPB: if (!boot_cpu_has(X86_FEATURE_IBPB)) { pr_err("WARNING: CPU does not support IBPB.\n"); - goto do_cmd_auto; - } else if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY)) { - retbleed_mitigation = RETBLEED_MITIGATION_IBPB; - } else { + retbleed_mitigation = RETBLEED_MITIGATION_AUTO; + } else if (!IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY)) { pr_err("WARNING: kernel not compiled with MITIGATION_IBPB_ENTRY.\n"); - goto do_cmd_auto; + retbleed_mitigation = RETBLEED_MITIGATION_AUTO; + } + break; + case RETBLEED_MITIGATION_STUFF: + if (!IS_ENABLED(CONFIG_MITIGATION_CALL_DEPTH_TRACKING)) { + pr_err("WARNING: kernel not compiled with MITIGATION_CALL_DEPTH_TRACKING.\n"); + retbleed_mitigation = RETBLEED_MITIGATION_AUTO; + } else if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) { + pr_err("WARNING: retbleed=stuff only supported for Intel CPUs.\n"); + retbleed_mitigation = RETBLEED_MITIGATION_AUTO; } break; + default: + break; + } - case RETBLEED_CMD_STUFF: - if (IS_ENABLED(CONFIG_MITIGATION_CALL_DEPTH_TRACKING) && - spectre_v2_enabled == SPECTRE_V2_RETPOLINE) { - if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) { - pr_err("WARNING: retbleed=stuff only supported for Intel CPUs.\n"); - goto do_cmd_auto; - } - retbleed_mitigation = RETBLEED_MITIGATION_STUFF; + if (retbleed_mitigation != RETBLEED_MITIGATION_AUTO) + return; - } else { - if (IS_ENABLED(CONFIG_MITIGATION_CALL_DEPTH_TRACKING)) - pr_err("WARNING: retbleed=stuff depends on spectre_v2=retpoline\n"); - else - pr_err("WARNING: kernel not compiled with MITIGATION_CALL_DEPTH_TRACKING.\n"); + /* Intel mitigation selected in retbleed_update_mitigation() */ + if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD || + boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) { + if (IS_ENABLED(CONFIG_MITIGATION_UNRET_ENTRY)) + retbleed_mitigation = RETBLEED_MITIGATION_UNRET; + else if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY) && + boot_cpu_has(X86_FEATURE_IBPB)) + retbleed_mitigation = RETBLEED_MITIGATION_IBPB; + else + retbleed_mitigation = RETBLEED_MITIGATION_NONE; + } +} - goto do_cmd_auto; - } - break; +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; -do_cmd_auto: - case RETBLEED_CMD_AUTO: - if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD || - boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) { - if (IS_ENABLED(CONFIG_MITIGATION_UNRET_ENTRY)) - retbleed_mitigation = RETBLEED_MITIGATION_UNRET; - else if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY) && - boot_cpu_has(X86_FEATURE_IBPB)) - retbleed_mitigation = RETBLEED_MITIGATION_IBPB; + /* + * retbleed=stuff is only allowed on Intel. If stuffing can't be used + * then a different mitigation will be selected below. + */ + if (retbleed_mitigation == RETBLEED_MITIGATION_STUFF) { + if (spectre_v2_enabled != SPECTRE_V2_RETPOLINE) { + pr_err("WARNING: retbleed=stuff depends on spectre_v2=retpoline\n"); + retbleed_mitigation = RETBLEED_MITIGATION_AUTO; } + } + /* + * Let IBRS trump all on Intel without affecting the effects of the + * retbleed= cmdline option except for call depth based stuffing + */ + if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) { + switch (spectre_v2_enabled) { + case SPECTRE_V2_IBRS: + retbleed_mitigation = RETBLEED_MITIGATION_IBRS; + break; + case SPECTRE_V2_EIBRS: + case SPECTRE_V2_EIBRS_RETPOLINE: + case SPECTRE_V2_EIBRS_LFENCE: + retbleed_mitigation = RETBLEED_MITIGATION_EIBRS; + break; + default: + 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]); +} - /* - * The Intel mitigation (IBRS or eIBRS) was already selected in - * spectre_v2_select_mitigation(). 'retbleed_mitigation' will - * be set accordingly below. - */ - break; - } +static void __init retbleed_apply_mitigation(void) +{ + bool mitigate_smt = false; switch (retbleed_mitigation) { + case RETBLEED_MITIGATION_NONE: + return; + case RETBLEED_MITIGATION_UNRET: setup_force_cpu_cap(X86_FEATURE_RETHUNK); setup_force_cpu_cap(X86_FEATURE_UNRET); @@ -1277,28 +1300,6 @@ do_cmd_auto: if (mitigate_smt && !boot_cpu_has(X86_FEATURE_STIBP) && (retbleed_nosmt || cpu_mitigations_auto_nosmt())) cpu_smt_disable(false); - - /* - * Let IBRS trump all on Intel without affecting the effects of the - * retbleed= cmdline option except for call depth based stuffing - */ - if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) { - switch (spectre_v2_enabled) { - case SPECTRE_V2_IBRS: - retbleed_mitigation = RETBLEED_MITIGATION_IBRS; - break; - case SPECTRE_V2_EIBRS: - case SPECTRE_V2_EIBRS_RETPOLINE: - case SPECTRE_V2_EIBRS_LFENCE: - retbleed_mitigation = RETBLEED_MITIGATION_EIBRS; - break; - default: - if (retbleed_mitigation != RETBLEED_MITIGATION_STUFF) - pr_err(RETBLEED_INTEL_MSG); - } - } - - pr_info("%s\n", retbleed_strings[retbleed_mitigation]); } #undef pr_fmt @@ -1855,8 +1856,8 @@ static void __init spectre_v2_select_mitigation(void) if (IS_ENABLED(CONFIG_MITIGATION_IBRS_ENTRY) && boot_cpu_has_bug(X86_BUG_RETBLEED) && - retbleed_cmd != RETBLEED_CMD_OFF && - retbleed_cmd != RETBLEED_CMD_STUFF && + 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; @@ -1964,7 +1965,7 @@ static void __init spectre_v2_select_mitigation(void) (boot_cpu_data.x86_vendor == X86_VENDOR_AMD || boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)) { - if (retbleed_cmd != RETBLEED_CMD_IBPB) { + if (retbleed_mitigation != RETBLEED_MITIGATION_IBPB) { setup_force_cpu_cap(X86_FEATURE_USE_IBPB_FW); pr_info("Enabling Speculation Barrier for firmware calls\n"); }