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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 <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Link: https://lore.kernel.org/r/20250819192200.2003074-4-david.kaplan@amd.com
This commit is contained in:
David Kaplan 2025-09-15 08:47:02 -05:00 committed by Borislav Petkov (AMD)
parent 9a9f8147ae
commit 02ac6cc8c5
2 changed files with 45 additions and 84 deletions
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1
arch/x86/include/asm/nospec-branch.h
View File

@ -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,

126
arch/x86/kernel/cpu/bugs.c
View File

@ -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",
@ -2543,93 +2535,60 @@ 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;
for (i = 0; i < ARRAY_SIZE(ssb_mitigation_options); i++) {
if (!match_option(arg, ret, ssb_mitigation_options[i].option))
continue;
cmd = ssb_mitigation_options[i].cmd;
break;
}
if (i >= ARRAY_SIZE(ssb_mitigation_options)) {
pr_err("unknown option (%s). Switching to default mode\n", arg);
return cmd;
}
}
return cmd;
nossb = true;
ssb_mode = SPEC_STORE_BYPASS_NONE;
return 0;
}
early_param("nospec_store_bypass_disable", nossb_parse_cmdline);
static int __init ssb_parse_cmdline(char *str)
{
if (!str)
return -EINVAL;
if (nossb)
return 0;
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 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))
if (!boot_cpu_has(X86_FEATURE_SSBD))
ssb_mode = SPEC_STORE_BYPASS_NONE;
pr_info("%s\n", ssb_strings[ssb_mode]);
}
@ -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))