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[PATCH v2 1/5] x86/bugs: Use early_param for spectre_v2_user

David Kaplan posted 5 patches 1 month, 2 weeks ago
There is a newer version of this series
[PATCH v2 1/5] x86/bugs: Use early_param for spectre_v2_user
Posted by David Kaplan 1 month, 2 weeks ago 
Most of the mitigations in bugs.c use early_param to parse their command
line options.  Modify spectre_v2_user to use early_param for consistency.

Remove spec_v2_user_print_cond() because informing a user about their
cmdline choice isn't very interesting and the chosen mitigation is already
printed in spectre_v2_user_update_mitigation().

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
 arch/x86/kernel/cpu/bugs.c | 65 +++++++++++++++-----------------------
 1 file changed, 26 insertions(+), 39 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 49ef1b832c1a..de78b76ae851 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1826,7 +1826,7 @@ enum spectre_v2_mitigation_cmd {
 
 static enum spectre_v2_mitigation_cmd spectre_v2_cmd __ro_after_init = SPECTRE_V2_CMD_AUTO;
 
-enum spectre_v2_user_cmd {
+enum spectre_v2_user_mitigation_cmd {
 	SPECTRE_V2_USER_CMD_NONE,
 	SPECTRE_V2_USER_CMD_AUTO,
 	SPECTRE_V2_USER_CMD_FORCE,
@@ -1836,6 +1836,9 @@ enum spectre_v2_user_cmd {
 	SPECTRE_V2_USER_CMD_SECCOMP_IBPB,
 };
 
+static enum spectre_v2_user_mitigation_cmd spectre_v2_user_cmd __ro_after_init =
+	SPECTRE_V2_USER_CMD_AUTO;
+
 static const char * const spectre_v2_user_strings[] = {
 	[SPECTRE_V2_USER_NONE]			= "User space: Vulnerable",
 	[SPECTRE_V2_USER_STRICT]		= "User space: Mitigation: STIBP protection",
@@ -1844,50 +1847,34 @@ static const char * const spectre_v2_user_strings[] = {
 	[SPECTRE_V2_USER_SECCOMP]		= "User space: Mitigation: STIBP via seccomp and prctl",
 };
 
-static const struct {
-	const char			*option;
-	enum spectre_v2_user_cmd	cmd;
-	bool				secure;
-} v2_user_options[] __initconst = {
-	{ "auto",		SPECTRE_V2_USER_CMD_AUTO,		false },
-	{ "off",		SPECTRE_V2_USER_CMD_NONE,		false },
-	{ "on",			SPECTRE_V2_USER_CMD_FORCE,		true  },
-	{ "prctl",		SPECTRE_V2_USER_CMD_PRCTL,		false },
-	{ "prctl,ibpb",		SPECTRE_V2_USER_CMD_PRCTL_IBPB,		false },
-	{ "seccomp",		SPECTRE_V2_USER_CMD_SECCOMP,		false },
-	{ "seccomp,ibpb",	SPECTRE_V2_USER_CMD_SECCOMP_IBPB,	false },
-};
-
-static void __init spec_v2_user_print_cond(const char *reason, bool secure)
-{
-	if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2) != secure)
-		pr_info("spectre_v2_user=%s forced on command line.\n", reason);
-}
-
-static enum spectre_v2_user_cmd __init spectre_v2_parse_user_cmdline(void)
+static int __init spectre_v2_parse_user_cmdline(char *str)
 {
-	char arg[20];
-	int ret, i;
+	if (!str)
+		return -EINVAL;
 
 	if (!IS_ENABLED(CONFIG_MITIGATION_SPECTRE_V2))
 		return SPECTRE_V2_USER_CMD_NONE;
 
-	ret = cmdline_find_option(boot_command_line, "spectre_v2_user",
-				  arg, sizeof(arg));
-	if (ret < 0)
-		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)) {
-			spec_v2_user_print_cond(v2_user_options[i].option,
-						v2_user_options[i].secure);
-			return v2_user_options[i].cmd;
-		}
-	}
+	if (!strcmp(str, "auto"))
+		spectre_v2_user_cmd = SPECTRE_V2_USER_CMD_AUTO;
+	else if (!strcmp(str, "off"))
+		spectre_v2_user_cmd = SPECTRE_V2_USER_CMD_NONE;
+	else if (!strcmp(str, "on"))
+		spectre_v2_user_cmd = SPECTRE_V2_USER_CMD_FORCE;
+	else if (!strcmp(str, "prctl"))
+		spectre_v2_user_cmd = SPECTRE_V2_USER_CMD_PRCTL;
+	else if (!strcmp(str, "prctl,ibpb"))
+		spectre_v2_user_cmd = SPECTRE_V2_USER_CMD_PRCTL_IBPB;
+	else if (!strcmp(str, "seccomp"))
+		spectre_v2_user_cmd = SPECTRE_V2_USER_CMD_SECCOMP;
+	else if (!strcmp(str, "seccomp,ibpb"))
+		spectre_v2_user_cmd = SPECTRE_V2_USER_CMD_SECCOMP_IBPB;
+	else
+		pr_err("Ignoring unknown spectre_v2_user option (%s).", str);
 
-	pr_err("Unknown user space protection option (%s). Switching to default\n", arg);
-	return SPECTRE_V2_USER_CMD_AUTO;
+	return 0;
 }
+early_param("spectre_v2_user", spectre_v2_parse_user_cmdline);
 
 static inline bool spectre_v2_in_ibrs_mode(enum spectre_v2_mitigation mode)
 {
@@ -1899,7 +1886,7 @@ static void __init spectre_v2_user_select_mitigation(void)
 	if (!boot_cpu_has(X86_FEATURE_IBPB) && !boot_cpu_has(X86_FEATURE_STIBP))
 		return;
 
-	switch (spectre_v2_parse_user_cmdline()) {
+	switch (spectre_v2_user_cmd) {
 	case SPECTRE_V2_USER_CMD_NONE:
 		return;
 	case SPECTRE_V2_USER_CMD_FORCE:
-- 
2.34.1
Re: [PATCH v2 1/5] x86/bugs: Use early_param for spectre_v2_user
Posted by Josh Poimboeuf 1 month, 1 week ago 
On Tue, Aug 19, 2025 at 02:21:56PM -0500, David Kaplan wrote:
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -1826,7 +1826,7 @@ enum spectre_v2_mitigation_cmd {
>  
>  static enum spectre_v2_mitigation_cmd spectre_v2_cmd __ro_after_init = SPECTRE_V2_CMD_AUTO;
>  
> -enum spectre_v2_user_cmd {
> +enum spectre_v2_user_mitigation_cmd {
>  	SPECTRE_V2_USER_CMD_NONE,
>  	SPECTRE_V2_USER_CMD_AUTO,
>  	SPECTRE_V2_USER_CMD_FORCE,
> @@ -1836,6 +1836,9 @@ enum spectre_v2_user_cmd {
>  	SPECTRE_V2_USER_CMD_SECCOMP_IBPB,
>  };
>  
> +static enum spectre_v2_user_mitigation_cmd spectre_v2_user_cmd __ro_after_init =
> +	SPECTRE_V2_USER_CMD_AUTO;

Should this default not be dependent on CONFIG_MITIGATION_SPECTRE_V2?

> -static enum spectre_v2_user_cmd __init spectre_v2_parse_user_cmdline(void)
> +static int __init spectre_v2_parse_user_cmdline(char *str)

Should probably swap "parse" and "user" to match the namespace of the
surrounding code, i.e. spectre_v2_user_parse_cmdline().  This is for
parsing the "spectre_v2_user" option after all.

>  {
> -	char arg[20];
> -	int ret, i;
> +	if (!str)
> +		return -EINVAL;
>  
>  	if (!IS_ENABLED(CONFIG_MITIGATION_SPECTRE_V2))
>  		return SPECTRE_V2_USER_CMD_NONE;

This return value no longer makes sense here, as this no longer returns
'enum spectre_v2_user_cmd'.

But also, most of the other mitigations allow you to override the
compile time default with the cmdline.  Might as well allow that here
too for consistency.

-- 
Josh
Re: [PATCH v2 1/5] x86/bugs: Use early_param for spectre_v2_user
Posted by Borislav Petkov 1 month, 2 weeks ago 
On Tue, Aug 19, 2025 at 02:21:56PM -0500, David Kaplan wrote:
> Most of the mitigations in bugs.c use early_param to parse their command
> line options.  Modify spectre_v2_user to use early_param for consistency.
> 
> Remove spec_v2_user_print_cond() because informing a user about their
> cmdline choice isn't very interesting and the chosen mitigation is already
> printed in spectre_v2_user_update_mitigation().
> 
> Signed-off-by: David Kaplan <david.kaplan@amd.com>
> ---
>  arch/x86/kernel/cpu/bugs.c | 65 +++++++++++++++-----------------------
>  1 file changed, 26 insertions(+), 39 deletions(-)

Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>

-- 
Regards/Gruss,
    Boris.

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