[PATCH 0/3] x86/cpu: Followups to adding setcpuid=

[PATCH 0/3] x86/cpu: Followups to adding setcpuid=

[Brendan Jackman]

To: Thomas Gleixner <tglx@linutronix.de>
To: Ingo Molnar <mingo@redhat.com>
To: Borislav Petkov <bp@alien8.de>
To: Dave Hansen <dave.hansen@linux.intel.com>
To: x86@kernel.org
To: H. Peter Anvin <hpa@zytor.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Brendan Jackman <jackmanb@google.com>

Followup to this patchset:

https://lore.kernel.org/linux-kernel/20250218-force-cpu-bug-v3-0-da3df43d1936@google.com/

Note that some of these changes were actually a part of that patchset
originally, but got lost as the v2 was merged, apparently due to
confusion stemming from Lore losing data.

---
Brendan Jackman (3):
      x86/cpu: Remove some macros about feature names
      x86/cpu: Warn louder about {set,clear}cpuid
      x86/cpu: Log CPU flag cmdline hacks more verbosely

 arch/x86/include/asm/cpufeature.h |  5 ----
 arch/x86/kernel/cpu/common.c      | 62 +++++++++++++++++++++++----------------
 2 files changed, 37 insertions(+), 30 deletions(-)
---
base-commit: ade3daf70f3655ea06606b2f65062ba4554db06e
change-id: 20250303-setcpuid-taint-louder-557bc93babed

Best regards,
-- 
Brendan Jackman <jackmanb@google.com>

[PATCH 1/3] x86/cpu: Remove some macros about feature names

[Brendan Jackman]

These macros used to abstract over CONFIG_X86_FEATURE_NAMES, but that
was removed in commit 7583e8fbdc49 ("x86/cpu: Remove
X86_FEATURE_NAMES"). Now they are just unnecessary indirection, remove
them.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/include/asm/cpufeature.h |  5 -----
 arch/x86/kernel/cpu/common.c      | 12 ++++++------
 2 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index de88f9b4fa3bfa7477bbdf7c5efe9582e1b87b4f..7937823ded89d08e1928ad6ca60ed8d76c65387d 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -38,13 +38,8 @@ enum cpuid_leafs
 	NR_CPUID_WORDS,
 };
 
-#define X86_CAP_FMT_NUM "%d:%d"
-#define x86_cap_flag_num(flag) ((flag) >> 5), ((flag) & 31)
-
 extern const char * const x86_cap_flags[NCAPINTS*32];
 extern const char * const x86_power_flags[32];
-#define X86_CAP_FMT "%s"
-#define x86_cap_flag(flag) x86_cap_flags[flag]
 
 /*
  * In order to save room, we index into this array by doing
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 0f32b6ffbf04f5394e15b50188c7d32943b0b111..b5fdaa6fd4c4ff7701009a0443ff57332503bc77 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -667,8 +667,8 @@ static void filter_cpuid_features(struct cpuinfo_x86 *c, bool warn)
 		if (!warn)
 			continue;
 
-		pr_warn("CPU: CPU feature " X86_CAP_FMT " disabled, no CPUID level 0x%x\n",
-			x86_cap_flag(df->feature), df->level);
+		pr_warn("CPU: CPU feature %s disabled, no CPUID level 0x%x\n",
+			x86_cap_flags[df->feature], df->level);
 	}
 }
 
@@ -1502,9 +1502,9 @@ static inline void parse_set_clear_cpuid(char *arg, bool set)
 
 				/* empty-string, i.e., ""-defined feature flags */
 				if (!x86_cap_flags[bit])
-					pr_cont(" " X86_CAP_FMT_NUM, x86_cap_flag_num(bit));
+					pr_cont(" %d:%d", bit >> 5, bit & 31);
 				else
-					pr_cont(" " X86_CAP_FMT, x86_cap_flag(bit));
+					pr_cont(" %s", x86_cap_flags[bit]);
 
 				if (set)
 					setup_force_cpu_cap(bit);
@@ -1523,9 +1523,9 @@ static inline void parse_set_clear_cpuid(char *arg, bool set)
 			const char *flag;
 
 			if (bit < 32 * NCAPINTS)
-				flag = x86_cap_flag(bit);
+				flag = x86_cap_flags[bit];
 			else
-				flag = x86_bug_flag(bit - (32 * NCAPINTS));
+				flag = x86_bug_flags[bit - (32 * NCAPINTS)];
 
 			if (!flag)
 				continue;

-- 
2.48.1.711.g2feabab25a-goog

[PATCH 2/3] x86/cpu: Warn louder about {set,clear}cpuid

[Brendan Jackman]

Commit 814165e9fd1f6 ("x86/cpu: Add the 'setcpuid=' boot parameter")
recently expanded the user's ability to break their system horribly by
overriding effective CPU flags. This was reflected with updates to the
documentation to try and make people aware that this is dangerous.

To further reduce the risk of users mistaking this for a "real feature",
and try to help them figure out why their kernel is tainted if they do
use it:

- Upgrade the existing printk to pr_warn, to help ensure kernel logs
  reflect what changes are in effect.

- Print an extra warning that tries to be as dramatic as possible, while
  also highlighting the fact that it tainted the kernel.

Suggested-by: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/kernel/cpu/common.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index b5fdaa6fd4c4ff7701009a0443ff57332503bc77..c1ced31f976d970efd24d6c9e4ac77cbff3371b9 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1479,12 +1479,12 @@ static void detect_nopl(void)
 #endif
 }
 
-static inline void parse_set_clear_cpuid(char *arg, bool set)
+static inline bool parse_set_clear_cpuid(char *arg, bool set)
 {
 	char *opt;
 	int taint = 0;
 
-	pr_info("%s CPUID bits:", set ? "Force-enabling" : "Clearing");
+	pr_warn("%s CPUID bits:", set ? "Force-enabling" : "Clearing");
 
 	while (arg) {
 		bool found __maybe_unused = false;
@@ -1547,10 +1547,9 @@ static inline void parse_set_clear_cpuid(char *arg, bool set)
 			pr_cont(" (unknown: %s)", opt);
 	}
 
-	if (taint)
-		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
-
 	pr_cont("\n");
+
+	return taint;
 }
 
 
@@ -1560,6 +1559,7 @@ static inline void parse_set_clear_cpuid(char *arg, bool set)
  */
 static void __init cpu_parse_early_param(void)
 {
+	bool cpuid_taint = false;
 	char arg[128];
 	int arglen;
 
@@ -1594,11 +1594,16 @@ static void __init cpu_parse_early_param(void)
 
 	arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
 	if (arglen > 0)
-		parse_set_clear_cpuid(arg, false);
+		cpuid_taint |= parse_set_clear_cpuid(arg, false);
 
 	arglen = cmdline_find_option(boot_command_line, "setcpuid", arg, sizeof(arg));
 	if (arglen > 0)
-		parse_set_clear_cpuid(arg, true);
+		cpuid_taint |= parse_set_clear_cpuid(arg, true);
+
+	if (cpuid_taint) {
+		pr_warn("!!! setcpuid=/clearcpuid= in use, this is for TESTING ONLY, may break things horribly. Tainting kernel.\n");
+		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+	}
 }
 
 /*

-- 
2.48.1.711.g2feabab25a-goog

[PATCH 3/3] x86/cpu: Log CPU flag cmdline hacks more verbosely

[Brendan Jackman]

Since using these options is very dangerous, make details as visible as
possible:

- Instead of a single message for each of the cmdline options, print a
  separate pr_warn() for each individual flag.

- Say explicitly whether the flag is a "feature" or a "bug".

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/kernel/cpu/common.c | 39 +++++++++++++++++++++++----------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index c1ced31f976d970efd24d6c9e4ac77cbff3371b9..8eba9ca9c216127ce1a6d630e7f67130520137b4 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1484,8 +1484,6 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 	char *opt;
 	int taint = 0;
 
-	pr_warn("%s CPUID bits:", set ? "Force-enabling" : "Clearing");
-
 	while (arg) {
 		bool found __maybe_unused = false;
 		unsigned int bit;
@@ -1500,16 +1498,19 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 		if (!kstrtouint(opt, 10, &bit)) {
 			if (bit < NCAPINTS * 32) {
 
+				if (set) {
+					pr_warn("setcpuid: force-enabling CPU feature flag:");
+					setup_force_cpu_cap(bit);
+				} else {
+					pr_warn("clearcpuid: force-disabling CPU feature flag:");
+					setup_clear_cpu_cap(bit);
+				}
 				/* empty-string, i.e., ""-defined feature flags */
 				if (!x86_cap_flags[bit])
-					pr_cont(" %d:%d", bit >> 5, bit & 31);
+					pr_cont(" %d:%d\n", bit >> 5, bit & 31);
 				else
-					pr_cont(" %s", x86_cap_flags[bit]);
+					pr_cont(" %s\n", x86_cap_flags[bit]);
 
-				if (set)
-					setup_force_cpu_cap(bit);
-				else
-					setup_clear_cpu_cap(bit);
 				taint++;
 			}
 			/*
@@ -1521,11 +1522,15 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 
 		for (bit = 0; bit < 32 * (NCAPINTS + NBUGINTS); bit++) {
 			const char *flag;
+			const char *kind;
 
-			if (bit < 32 * NCAPINTS)
+			if (bit < 32 * NCAPINTS) {
 				flag = x86_cap_flags[bit];
-			else
+				kind = "feature";
+			} else {
+				kind = "bug";
 				flag = x86_bug_flags[bit - (32 * NCAPINTS)];
+			}
 
 			if (!flag)
 				continue;
@@ -1533,22 +1538,24 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 			if (strcmp(flag, opt))
 				continue;
 
-			pr_cont(" %s", opt);
-			if (set)
+			if (set) {
+				pr_warn("setcpuid: force-enabling CPU %s flag: %s\n",
+					kind, flag);
 				setup_force_cpu_cap(bit);
-			else
+			} else {
+				pr_warn("clearcpuid: force-disabling CPU %s flag: %s\n",
+					kind, flag);
 				setup_clear_cpu_cap(bit);
+			}
 			taint++;
 			found = true;
 			break;
 		}
 
 		if (!found)
-			pr_cont(" (unknown: %s)", opt);
+			pr_warn("%s: unknown CPU flag: %s", set ? "setcpuid" : "clearcpuid", opt);
 	}
 
-	pr_cont("\n");
-
 	return taint;
 }
 

-- 
2.48.1.711.g2feabab25a-goog

Re: [PATCH 0/3] x86/cpu: Followups to adding setcpuid=

[Borislav Petkov]

On Mon, Mar 03, 2025 at 03:45:36PM +0000, Brendan Jackman wrote:
> To: Thomas Gleixner <tglx@linutronix.de>
> To: Ingo Molnar <mingo@redhat.com>
> To: Borislav Petkov <bp@alien8.de>
> To: Dave Hansen <dave.hansen@linux.intel.com>
> To: x86@kernel.org
> To: H. Peter Anvin <hpa@zytor.com>
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> 
> Followup to this patchset:
> 
> https://lore.kernel.org/linux-kernel/20250218-force-cpu-bug-v3-0-da3df43d1936@google.com/
> 
> Note that some of these changes were actually a part of that patchset
> originally, but got lost as the v2 was merged, apparently due to
> confusion stemming from Lore losing data.
> 
> ---
> Brendan Jackman (3):
>       x86/cpu: Remove some macros about feature names
>       x86/cpu: Warn louder about {set,clear}cpuid
>       x86/cpu: Log CPU flag cmdline hacks more verbosely
> 
>  arch/x86/include/asm/cpufeature.h |  5 ----
>  arch/x86/kernel/cpu/common.c      | 62 +++++++++++++++++++++++----------------
>  2 files changed, 37 insertions(+), 30 deletions(-)
> ---

LGTM.

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

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

[tip: x86/cpu] x86/cpu: Log CPU flag cmdline hacks more verbosely

[tip-bot2 for Brendan Jackman]

The following commit has been merged into the x86/cpu branch of tip:

Commit-ID:     75ab6506acbc494a838dc8bc5fbbde7092f71b33
Gitweb:        https://git.kernel.org/tip/75ab6506acbc494a838dc8bc5fbbde7092f71b33
Author:        Brendan Jackman <jackmanb@google.com>
AuthorDate:    Mon, 03 Mar 2025 15:45:39 
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 03 Mar 2025 21:23:39 +01:00

x86/cpu: Log CPU flag cmdline hacks more verbosely

Since using these options is very dangerous, make details as visible as
possible:

- Instead of a single message for each of the cmdline options, print a
  separate pr_warn() for each individual flag.

- Say explicitly whether the flag is a "feature" or a "bug".

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250303-setcpuid-taint-louder-v1-3-8d255032cb4c@google.com
---
 arch/x86/kernel/cpu/common.c | 39 ++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index c1ced31..8eba9ca 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1484,8 +1484,6 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 	char *opt;
 	int taint = 0;
 
-	pr_warn("%s CPUID bits:", set ? "Force-enabling" : "Clearing");
-
 	while (arg) {
 		bool found __maybe_unused = false;
 		unsigned int bit;
@@ -1500,16 +1498,19 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 		if (!kstrtouint(opt, 10, &bit)) {
 			if (bit < NCAPINTS * 32) {
 
+				if (set) {
+					pr_warn("setcpuid: force-enabling CPU feature flag:");
+					setup_force_cpu_cap(bit);
+				} else {
+					pr_warn("clearcpuid: force-disabling CPU feature flag:");
+					setup_clear_cpu_cap(bit);
+				}
 				/* empty-string, i.e., ""-defined feature flags */
 				if (!x86_cap_flags[bit])
-					pr_cont(" %d:%d", bit >> 5, bit & 31);
+					pr_cont(" %d:%d\n", bit >> 5, bit & 31);
 				else
-					pr_cont(" %s", x86_cap_flags[bit]);
+					pr_cont(" %s\n", x86_cap_flags[bit]);
 
-				if (set)
-					setup_force_cpu_cap(bit);
-				else
-					setup_clear_cpu_cap(bit);
 				taint++;
 			}
 			/*
@@ -1521,11 +1522,15 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 
 		for (bit = 0; bit < 32 * (NCAPINTS + NBUGINTS); bit++) {
 			const char *flag;
+			const char *kind;
 
-			if (bit < 32 * NCAPINTS)
+			if (bit < 32 * NCAPINTS) {
 				flag = x86_cap_flags[bit];
-			else
+				kind = "feature";
+			} else {
+				kind = "bug";
 				flag = x86_bug_flags[bit - (32 * NCAPINTS)];
+			}
 
 			if (!flag)
 				continue;
@@ -1533,22 +1538,24 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 			if (strcmp(flag, opt))
 				continue;
 
-			pr_cont(" %s", opt);
-			if (set)
+			if (set) {
+				pr_warn("setcpuid: force-enabling CPU %s flag: %s\n",
+					kind, flag);
 				setup_force_cpu_cap(bit);
-			else
+			} else {
+				pr_warn("clearcpuid: force-disabling CPU %s flag: %s\n",
+					kind, flag);
 				setup_clear_cpu_cap(bit);
+			}
 			taint++;
 			found = true;
 			break;
 		}
 
 		if (!found)
-			pr_cont(" (unknown: %s)", opt);
+			pr_warn("%s: unknown CPU flag: %s", set ? "setcpuid" : "clearcpuid", opt);
 	}
 
-	pr_cont("\n");
-
 	return taint;
 }
 

[tip: x86/cpu] x86/cpu: Warn louder about the {set,clear}cpuid boot parameters

[tip-bot2 for Brendan Jackman]

The following commit has been merged into the x86/cpu branch of tip:

Commit-ID:     cf4d8a642cb8556c3cb786278a6f7fa43bc3f5e9
Gitweb:        https://git.kernel.org/tip/cf4d8a642cb8556c3cb786278a6f7fa43bc3f5e9
Author:        Brendan Jackman <jackmanb@google.com>
AuthorDate:    Mon, 03 Mar 2025 15:45:38 
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 03 Mar 2025 21:23:39 +01:00

x86/cpu: Warn louder about the {set,clear}cpuid boot parameters

Commit 814165e9fd1f6 ("x86/cpu: Add the 'setcpuid=' boot parameter")
recently expanded the user's ability to break their system horribly by
overriding effective CPU flags. This was reflected with updates to the
documentation to try and make people aware that this is dangerous.

To further reduce the risk of users mistaking this for a "real feature",
and try to help them figure out why their kernel is tainted if they do
use it:

- Upgrade the existing printk to pr_warn, to help ensure kernel logs
  reflect what changes are in effect.

- Print an extra warning that tries to be as dramatic as possible, while
  also highlighting the fact that it tainted the kernel.

Suggested-by: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250303-setcpuid-taint-louder-v1-2-8d255032cb4c@google.com
---
 arch/x86/kernel/cpu/common.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index b5fdaa6..c1ced31 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1479,12 +1479,12 @@ static void detect_nopl(void)
 #endif
 }
 
-static inline void parse_set_clear_cpuid(char *arg, bool set)
+static inline bool parse_set_clear_cpuid(char *arg, bool set)
 {
 	char *opt;
 	int taint = 0;
 
-	pr_info("%s CPUID bits:", set ? "Force-enabling" : "Clearing");
+	pr_warn("%s CPUID bits:", set ? "Force-enabling" : "Clearing");
 
 	while (arg) {
 		bool found __maybe_unused = false;
@@ -1547,10 +1547,9 @@ static inline void parse_set_clear_cpuid(char *arg, bool set)
 			pr_cont(" (unknown: %s)", opt);
 	}
 
-	if (taint)
-		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
-
 	pr_cont("\n");
+
+	return taint;
 }
 
 
@@ -1560,6 +1559,7 @@ static inline void parse_set_clear_cpuid(char *arg, bool set)
  */
 static void __init cpu_parse_early_param(void)
 {
+	bool cpuid_taint = false;
 	char arg[128];
 	int arglen;
 
@@ -1594,11 +1594,16 @@ static void __init cpu_parse_early_param(void)
 
 	arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
 	if (arglen > 0)
-		parse_set_clear_cpuid(arg, false);
+		cpuid_taint |= parse_set_clear_cpuid(arg, false);
 
 	arglen = cmdline_find_option(boot_command_line, "setcpuid", arg, sizeof(arg));
 	if (arglen > 0)
-		parse_set_clear_cpuid(arg, true);
+		cpuid_taint |= parse_set_clear_cpuid(arg, true);
+
+	if (cpuid_taint) {
+		pr_warn("!!! setcpuid=/clearcpuid= in use, this is for TESTING ONLY, may break things horribly. Tainting kernel.\n");
+		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+	}
 }
 
 /*

[tip: x86/cpu] x86/cpu: Remove unnecessary macro indirection related to CPU feature names

[tip-bot2 for Brendan Jackman]

The following commit has been merged into the x86/cpu branch of tip:

Commit-ID:     2f0f6cdf9bc1d104c8c224df8dd65748de02118d
Gitweb:        https://git.kernel.org/tip/2f0f6cdf9bc1d104c8c224df8dd65748de02118d
Author:        Brendan Jackman <jackmanb@google.com>
AuthorDate:    Mon, 03 Mar 2025 15:45:37 
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 03 Mar 2025 21:23:39 +01:00

x86/cpu: Remove unnecessary macro indirection related to CPU feature names

These macros used to abstract over CONFIG_X86_FEATURE_NAMES, but that
was removed in:

  7583e8fbdc49 ("x86/cpu: Remove X86_FEATURE_NAMES")

Now they are just an unnecessary indirection, remove them.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250303-setcpuid-taint-louder-v1-1-8d255032cb4c@google.com
---
 arch/x86/include/asm/cpufeature.h |  5 -----
 arch/x86/kernel/cpu/common.c      | 12 ++++++------
 2 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index de88f9b..7937823 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -38,13 +38,8 @@ enum cpuid_leafs
 	NR_CPUID_WORDS,
 };
 
-#define X86_CAP_FMT_NUM "%d:%d"
-#define x86_cap_flag_num(flag) ((flag) >> 5), ((flag) & 31)
-
 extern const char * const x86_cap_flags[NCAPINTS*32];
 extern const char * const x86_power_flags[32];
-#define X86_CAP_FMT "%s"
-#define x86_cap_flag(flag) x86_cap_flags[flag]
 
 /*
  * In order to save room, we index into this array by doing
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 0f32b6f..b5fdaa6 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -667,8 +667,8 @@ static void filter_cpuid_features(struct cpuinfo_x86 *c, bool warn)
 		if (!warn)
 			continue;
 
-		pr_warn("CPU: CPU feature " X86_CAP_FMT " disabled, no CPUID level 0x%x\n",
-			x86_cap_flag(df->feature), df->level);
+		pr_warn("CPU: CPU feature %s disabled, no CPUID level 0x%x\n",
+			x86_cap_flags[df->feature], df->level);
 	}
 }
 
@@ -1502,9 +1502,9 @@ static inline void parse_set_clear_cpuid(char *arg, bool set)
 
 				/* empty-string, i.e., ""-defined feature flags */
 				if (!x86_cap_flags[bit])
-					pr_cont(" " X86_CAP_FMT_NUM, x86_cap_flag_num(bit));
+					pr_cont(" %d:%d", bit >> 5, bit & 31);
 				else
-					pr_cont(" " X86_CAP_FMT, x86_cap_flag(bit));
+					pr_cont(" %s", x86_cap_flags[bit]);
 
 				if (set)
 					setup_force_cpu_cap(bit);
@@ -1523,9 +1523,9 @@ static inline void parse_set_clear_cpuid(char *arg, bool set)
 			const char *flag;
 
 			if (bit < 32 * NCAPINTS)
-				flag = x86_cap_flag(bit);
+				flag = x86_cap_flags[bit];
 			else
-				flag = x86_bug_flag(bit - (32 * NCAPINTS));
+				flag = x86_bug_flags[bit - (32 * NCAPINTS)];
 
 			if (!flag)
 				continue;

[tip: x86/cpu] x86/cpu: Log CPU flag cmdline hacks more verbosely

[tip-bot2 for Brendan Jackman]

The following commit has been merged into the x86/cpu branch of tip:

Commit-ID:     d0ba9bcf001c7907e4755b0e498f5ff9d1a228ef
Gitweb:        https://git.kernel.org/tip/d0ba9bcf001c7907e4755b0e498f5ff9d1a228ef
Author:        Brendan Jackman <jackmanb@google.com>
AuthorDate:    Mon, 03 Mar 2025 15:45:39 
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 04 Mar 2025 11:15:12 +01:00

x86/cpu: Log CPU flag cmdline hacks more verbosely

Since using these options is very dangerous, make details as visible as
possible:

- Instead of a single message for each of the cmdline options, print a
  separate pr_warn() for each individual flag.

- Say explicitly whether the flag is a "feature" or a "bug".

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250303-setcpuid-taint-louder-v1-3-8d255032cb4c@google.com
---
 arch/x86/kernel/cpu/common.c | 39 ++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index c1ced31..8eba9ca 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1484,8 +1484,6 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 	char *opt;
 	int taint = 0;
 
-	pr_warn("%s CPUID bits:", set ? "Force-enabling" : "Clearing");
-
 	while (arg) {
 		bool found __maybe_unused = false;
 		unsigned int bit;
@@ -1500,16 +1498,19 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 		if (!kstrtouint(opt, 10, &bit)) {
 			if (bit < NCAPINTS * 32) {
 
+				if (set) {
+					pr_warn("setcpuid: force-enabling CPU feature flag:");
+					setup_force_cpu_cap(bit);
+				} else {
+					pr_warn("clearcpuid: force-disabling CPU feature flag:");
+					setup_clear_cpu_cap(bit);
+				}
 				/* empty-string, i.e., ""-defined feature flags */
 				if (!x86_cap_flags[bit])
-					pr_cont(" %d:%d", bit >> 5, bit & 31);
+					pr_cont(" %d:%d\n", bit >> 5, bit & 31);
 				else
-					pr_cont(" %s", x86_cap_flags[bit]);
+					pr_cont(" %s\n", x86_cap_flags[bit]);
 
-				if (set)
-					setup_force_cpu_cap(bit);
-				else
-					setup_clear_cpu_cap(bit);
 				taint++;
 			}
 			/*
@@ -1521,11 +1522,15 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 
 		for (bit = 0; bit < 32 * (NCAPINTS + NBUGINTS); bit++) {
 			const char *flag;
+			const char *kind;
 
-			if (bit < 32 * NCAPINTS)
+			if (bit < 32 * NCAPINTS) {
 				flag = x86_cap_flags[bit];
-			else
+				kind = "feature";
+			} else {
+				kind = "bug";
 				flag = x86_bug_flags[bit - (32 * NCAPINTS)];
+			}
 
 			if (!flag)
 				continue;
@@ -1533,22 +1538,24 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 			if (strcmp(flag, opt))
 				continue;
 
-			pr_cont(" %s", opt);
-			if (set)
+			if (set) {
+				pr_warn("setcpuid: force-enabling CPU %s flag: %s\n",
+					kind, flag);
 				setup_force_cpu_cap(bit);
-			else
+			} else {
+				pr_warn("clearcpuid: force-disabling CPU %s flag: %s\n",
+					kind, flag);
 				setup_clear_cpu_cap(bit);
+			}
 			taint++;
 			found = true;
 			break;
 		}
 
 		if (!found)
-			pr_cont(" (unknown: %s)", opt);
+			pr_warn("%s: unknown CPU flag: %s", set ? "setcpuid" : "clearcpuid", opt);
 	}
 
-	pr_cont("\n");
-
 	return taint;
 }
 

[tip: x86/cpu] x86/cpu: Warn louder about the {set,clear}cpuid boot parameters

[tip-bot2 for Brendan Jackman]

The following commit has been merged into the x86/cpu branch of tip:

Commit-ID:     681955761bf6845241c6d33e2fb222f5e92c8b89
Gitweb:        https://git.kernel.org/tip/681955761bf6845241c6d33e2fb222f5e92c8b89
Author:        Brendan Jackman <jackmanb@google.com>
AuthorDate:    Mon, 03 Mar 2025 15:45:38 
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 04 Mar 2025 11:15:03 +01:00

x86/cpu: Warn louder about the {set,clear}cpuid boot parameters

Commit 814165e9fd1f6 ("x86/cpu: Add the 'setcpuid=' boot parameter")
recently expanded the user's ability to break their system horribly by
overriding effective CPU flags. This was reflected with updates to the
documentation to try and make people aware that this is dangerous.

To further reduce the risk of users mistaking this for a "real feature",
and try to help them figure out why their kernel is tainted if they do
use it:

- Upgrade the existing printk to pr_warn, to help ensure kernel logs
  reflect what changes are in effect.

- Print an extra warning that tries to be as dramatic as possible, while
  also highlighting the fact that it tainted the kernel.

Suggested-by: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250303-setcpuid-taint-louder-v1-2-8d255032cb4c@google.com
---
 arch/x86/kernel/cpu/common.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index b5fdaa6..c1ced31 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1479,12 +1479,12 @@ static void detect_nopl(void)
 #endif
 }
 
-static inline void parse_set_clear_cpuid(char *arg, bool set)
+static inline bool parse_set_clear_cpuid(char *arg, bool set)
 {
 	char *opt;
 	int taint = 0;
 
-	pr_info("%s CPUID bits:", set ? "Force-enabling" : "Clearing");
+	pr_warn("%s CPUID bits:", set ? "Force-enabling" : "Clearing");
 
 	while (arg) {
 		bool found __maybe_unused = false;
@@ -1547,10 +1547,9 @@ static inline void parse_set_clear_cpuid(char *arg, bool set)
 			pr_cont(" (unknown: %s)", opt);
 	}
 
-	if (taint)
-		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
-
 	pr_cont("\n");
+
+	return taint;
 }
 
 
@@ -1560,6 +1559,7 @@ static inline void parse_set_clear_cpuid(char *arg, bool set)
  */
 static void __init cpu_parse_early_param(void)
 {
+	bool cpuid_taint = false;
 	char arg[128];
 	int arglen;
 
@@ -1594,11 +1594,16 @@ static void __init cpu_parse_early_param(void)
 
 	arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
 	if (arglen > 0)
-		parse_set_clear_cpuid(arg, false);
+		cpuid_taint |= parse_set_clear_cpuid(arg, false);
 
 	arglen = cmdline_find_option(boot_command_line, "setcpuid", arg, sizeof(arg));
 	if (arglen > 0)
-		parse_set_clear_cpuid(arg, true);
+		cpuid_taint |= parse_set_clear_cpuid(arg, true);
+
+	if (cpuid_taint) {
+		pr_warn("!!! setcpuid=/clearcpuid= in use, this is for TESTING ONLY, may break things horribly. Tainting kernel.\n");
+		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+	}
 }
 
 /*

[tip: x86/cpu] x86/cpu: Remove unnecessary macro indirection related to CPU feature names

[tip-bot2 for Brendan Jackman]

The following commit has been merged into the x86/cpu branch of tip:

Commit-ID:     27c3b452c1a554483ac692702639c826602d1089
Gitweb:        https://git.kernel.org/tip/27c3b452c1a554483ac692702639c826602d1089
Author:        Brendan Jackman <jackmanb@google.com>
AuthorDate:    Mon, 03 Mar 2025 15:45:37 
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 04 Mar 2025 11:14:53 +01:00

x86/cpu: Remove unnecessary macro indirection related to CPU feature names

These macros used to abstract over CONFIG_X86_FEATURE_NAMES, but that
was removed in:

  7583e8fbdc49 ("x86/cpu: Remove X86_FEATURE_NAMES")

Now they are just an unnecessary indirection, remove them.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250303-setcpuid-taint-louder-v1-1-8d255032cb4c@google.com
---
 arch/x86/include/asm/cpufeature.h |  5 -----
 arch/x86/kernel/cpu/common.c      | 12 ++++++------
 2 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index e5fc003..e955da3 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -37,13 +37,8 @@ enum cpuid_leafs
 	NR_CPUID_WORDS,
 };
 
-#define X86_CAP_FMT_NUM "%d:%d"
-#define x86_cap_flag_num(flag) ((flag) >> 5), ((flag) & 31)
-
 extern const char * const x86_cap_flags[NCAPINTS*32];
 extern const char * const x86_power_flags[32];
-#define X86_CAP_FMT "%s"
-#define x86_cap_flag(flag) x86_cap_flags[flag]
 
 /*
  * In order to save room, we index into this array by doing
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 0f32b6f..b5fdaa6 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -667,8 +667,8 @@ static void filter_cpuid_features(struct cpuinfo_x86 *c, bool warn)
 		if (!warn)
 			continue;
 
-		pr_warn("CPU: CPU feature " X86_CAP_FMT " disabled, no CPUID level 0x%x\n",
-			x86_cap_flag(df->feature), df->level);
+		pr_warn("CPU: CPU feature %s disabled, no CPUID level 0x%x\n",
+			x86_cap_flags[df->feature], df->level);
 	}
 }
 
@@ -1502,9 +1502,9 @@ static inline void parse_set_clear_cpuid(char *arg, bool set)
 
 				/* empty-string, i.e., ""-defined feature flags */
 				if (!x86_cap_flags[bit])
-					pr_cont(" " X86_CAP_FMT_NUM, x86_cap_flag_num(bit));
+					pr_cont(" %d:%d", bit >> 5, bit & 31);
 				else
-					pr_cont(" " X86_CAP_FMT, x86_cap_flag(bit));
+					pr_cont(" %s", x86_cap_flags[bit]);
 
 				if (set)
 					setup_force_cpu_cap(bit);
@@ -1523,9 +1523,9 @@ static inline void parse_set_clear_cpuid(char *arg, bool set)
 			const char *flag;
 
 			if (bit < 32 * NCAPINTS)
-				flag = x86_cap_flag(bit);
+				flag = x86_cap_flags[bit];
 			else
-				flag = x86_bug_flag(bit - (32 * NCAPINTS));
+				flag = x86_bug_flags[bit - (32 * NCAPINTS)];
 
 			if (!flag)
 				continue;