From: David Kaplan Date: Mon, 15 Sep 2025 13:47:02 +0000 (-0500) Subject: x86/bugs: Simplify SSB cmdline parsing X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=02ac6cc8c5a129013695c3eee48b65fb5ba669c0;p=users%2Fhch%2Fmisc.git x86/bugs: Simplify SSB cmdline parsing Simplify the SSB command line parsing by selecting a mitigation directly, as is done in most of the simpler vulnerabilities. Use early_param() instead of cmdline_find_option() for consistency with the other mitigation selections. Signed-off-by: David Kaplan Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Pawan Gupta Link: https://lore.kernel.org/r/20250819192200.2003074-4-david.kaplan@amd.com --- diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index e29f82466f43..08ed5a2e46a5 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -514,6 +514,7 @@ enum spectre_v2_user_mitigation { /* The Speculative Store Bypass disable variants */ enum ssb_mitigation { SPEC_STORE_BYPASS_NONE, + SPEC_STORE_BYPASS_AUTO, SPEC_STORE_BYPASS_DISABLE, SPEC_STORE_BYPASS_PRCTL, SPEC_STORE_BYPASS_SECCOMP, diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index c348f14c2b5a..570de55485df 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -2525,16 +2525,8 @@ static void update_mds_branch_idle(void) #undef pr_fmt #define pr_fmt(fmt) "Speculative Store Bypass: " fmt -static enum ssb_mitigation ssb_mode __ro_after_init = SPEC_STORE_BYPASS_NONE; - -/* The kernel command line selection */ -enum ssb_mitigation_cmd { - SPEC_STORE_BYPASS_CMD_NONE, - SPEC_STORE_BYPASS_CMD_AUTO, - SPEC_STORE_BYPASS_CMD_ON, - SPEC_STORE_BYPASS_CMD_PRCTL, - SPEC_STORE_BYPASS_CMD_SECCOMP, -}; +static enum ssb_mitigation ssb_mode __ro_after_init = + IS_ENABLED(CONFIG_MITIGATION_SSB) ? SPEC_STORE_BYPASS_AUTO : SPEC_STORE_BYPASS_NONE; static const char * const ssb_strings[] = { [SPEC_STORE_BYPASS_NONE] = "Vulnerable", @@ -2543,94 +2535,61 @@ static const char * const ssb_strings[] = { [SPEC_STORE_BYPASS_SECCOMP] = "Mitigation: Speculative Store Bypass disabled via prctl and seccomp", }; -static const struct { - const char *option; - enum ssb_mitigation_cmd cmd; -} ssb_mitigation_options[] __initconst = { - { "auto", SPEC_STORE_BYPASS_CMD_AUTO }, /* Platform decides */ - { "on", SPEC_STORE_BYPASS_CMD_ON }, /* Disable Speculative Store Bypass */ - { "off", SPEC_STORE_BYPASS_CMD_NONE }, /* Don't touch Speculative Store Bypass */ - { "prctl", SPEC_STORE_BYPASS_CMD_PRCTL }, /* Disable Speculative Store Bypass via prctl */ - { "seccomp", SPEC_STORE_BYPASS_CMD_SECCOMP }, /* Disable Speculative Store Bypass via prctl and seccomp */ -}; +static bool nossb __ro_after_init; -static enum ssb_mitigation_cmd __init ssb_parse_cmdline(void) +static int __init nossb_parse_cmdline(char *str) { - enum ssb_mitigation_cmd cmd; - char arg[20]; - int ret, i; - - cmd = IS_ENABLED(CONFIG_MITIGATION_SSB) ? - SPEC_STORE_BYPASS_CMD_AUTO : SPEC_STORE_BYPASS_CMD_NONE; - if (cmdline_find_option_bool(boot_command_line, "nospec_store_bypass_disable") || - cpu_mitigations_off()) { - return SPEC_STORE_BYPASS_CMD_NONE; - } else { - ret = cmdline_find_option(boot_command_line, "spec_store_bypass_disable", - arg, sizeof(arg)); - if (ret < 0) - return cmd; + nossb = true; + ssb_mode = SPEC_STORE_BYPASS_NONE; + return 0; +} +early_param("nospec_store_bypass_disable", nossb_parse_cmdline); - for (i = 0; i < ARRAY_SIZE(ssb_mitigation_options); i++) { - if (!match_option(arg, ret, ssb_mitigation_options[i].option)) - continue; +static int __init ssb_parse_cmdline(char *str) +{ + if (!str) + return -EINVAL; - cmd = ssb_mitigation_options[i].cmd; - break; - } + if (nossb) + return 0; - if (i >= ARRAY_SIZE(ssb_mitigation_options)) { - pr_err("unknown option (%s). Switching to default mode\n", arg); - return cmd; - } - } + if (!strcmp(str, "auto")) + ssb_mode = SPEC_STORE_BYPASS_AUTO; + else if (!strcmp(str, "on")) + ssb_mode = SPEC_STORE_BYPASS_DISABLE; + else if (!strcmp(str, "off")) + ssb_mode = SPEC_STORE_BYPASS_NONE; + else if (!strcmp(str, "prctl")) + ssb_mode = SPEC_STORE_BYPASS_PRCTL; + else if (!strcmp(str, "seccomp")) + ssb_mode = IS_ENABLED(CONFIG_SECCOMP) ? + SPEC_STORE_BYPASS_SECCOMP : SPEC_STORE_BYPASS_PRCTL; + else + pr_err("Ignoring unknown spec_store_bypass_disable option (%s).\n", + str); - return cmd; + return 0; } +early_param("spec_store_bypass_disable", ssb_parse_cmdline); static void __init ssb_select_mitigation(void) { - enum ssb_mitigation_cmd cmd; - - if (!boot_cpu_has(X86_FEATURE_SSBD)) - goto out; - - cmd = ssb_parse_cmdline(); - if (!boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS) && - (cmd == SPEC_STORE_BYPASS_CMD_NONE || - cmd == SPEC_STORE_BYPASS_CMD_AUTO)) + if (!boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS)) { + ssb_mode = SPEC_STORE_BYPASS_NONE; return; + } - switch (cmd) { - case SPEC_STORE_BYPASS_CMD_SECCOMP: - /* - * Choose prctl+seccomp as the default mode if seccomp is - * enabled. - */ - if (IS_ENABLED(CONFIG_SECCOMP)) - ssb_mode = SPEC_STORE_BYPASS_SECCOMP; - else - ssb_mode = SPEC_STORE_BYPASS_PRCTL; - break; - case SPEC_STORE_BYPASS_CMD_ON: - ssb_mode = SPEC_STORE_BYPASS_DISABLE; - break; - case SPEC_STORE_BYPASS_CMD_AUTO: + if (ssb_mode == SPEC_STORE_BYPASS_AUTO) { if (should_mitigate_vuln(X86_BUG_SPEC_STORE_BYPASS)) ssb_mode = SPEC_STORE_BYPASS_PRCTL; else ssb_mode = SPEC_STORE_BYPASS_NONE; - break; - case SPEC_STORE_BYPASS_CMD_PRCTL: - ssb_mode = SPEC_STORE_BYPASS_PRCTL; - break; - case SPEC_STORE_BYPASS_CMD_NONE: - break; } -out: - if (boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS)) - pr_info("%s\n", ssb_strings[ssb_mode]); + if (!boot_cpu_has(X86_FEATURE_SSBD)) + ssb_mode = SPEC_STORE_BYPASS_NONE; + + pr_info("%s\n", ssb_strings[ssb_mode]); } static void __init ssb_apply_mitigation(void) @@ -2846,6 +2805,7 @@ static int ssb_prctl_get(struct task_struct *task) return PR_SPEC_DISABLE; case SPEC_STORE_BYPASS_SECCOMP: case SPEC_STORE_BYPASS_PRCTL: + case SPEC_STORE_BYPASS_AUTO: if (task_spec_ssb_force_disable(task)) return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE; if (task_spec_ssb_noexec(task))