[PATCH v7 2/3] x86/cpu: Check if feature string is non-zero

[Maciej Wieczor-Retman]

From: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>

In filter_cpuid_features, x86_cap_flags[] is read, but it's not verified
whether the string is non-zero which could lead to unwanted output.

In two more places there are open coded paths that try to retrieve a
feature string, and if there isn't one, the feature word and bit are
returned instead. While correcting filter_cpuid_features() with a helper
it's trivial to also clean up these open coded cases.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
---
Changelog v7:
- sizeof(buf) -> 16
- Rebase onto 7.01-rc1.

Changelog v6:
- Remove parts of the patch message that are redundant and just copy
  what's visible in the diff.
- Redo the helper to use an external char buffer instead of a local
  static string.

 arch/x86/kernel/cpu/common.c     | 26 +++++++++++++++++++++-----
 arch/x86/kernel/cpu/cpuid-deps.c | 20 +++-----------------
 include/linux/cpu.h              |  2 ++
 3 files changed, 26 insertions(+), 22 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 9aa11224a038..b60269174d95 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -675,6 +675,7 @@ cpuid_dependent_features[] = {
 static void filter_cpuid_features(struct cpuinfo_x86 *c, bool warn)
 {
 	const struct cpuid_dependent_feature *df;
+	char feature_buf[16];
 
 	for (df = cpuid_dependent_features; df->feature; df++) {
 
@@ -697,7 +698,7 @@ static void filter_cpuid_features(struct cpuinfo_x86 *c, bool warn)
 			continue;
 
 		pr_warn("CPU: CPU feature %s disabled, no CPUID level 0x%x\n",
-			x86_cap_flags[df->feature], df->level);
+			x86_cap_name(df->feature, feature_buf), df->level);
 	}
 }
 
@@ -1634,6 +1635,7 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 
 	while (arg) {
 		bool found __maybe_unused = false;
+		char name_buf[16];
 		unsigned int bit;
 
 		opt = strsep(&arg, ",");
@@ -1654,10 +1656,7 @@ static inline bool parse_set_clear_cpuid(char *arg, bool set)
 					setup_clear_cpu_cap(bit);
 				}
 				/* empty-string, i.e., ""-defined feature flags */
-				if (!x86_cap_flags[bit])
-					pr_cont(" %d:%d\n", bit >> 5, bit & 31);
-				else
-					pr_cont(" %s\n", x86_cap_flags[bit]);
+				pr_cont(" %s\n", x86_cap_name(bit, name_buf));
 
 				taint++;
 			}
@@ -1980,6 +1979,23 @@ static void generic_identify(struct cpuinfo_x86 *c)
 #endif
 }
 
+const char *x86_cap_name(unsigned int bit, char *buf)
+{
+	unsigned int word = bit >> 5;
+	const char *name = NULL;
+
+	if (likely(word < NCAPINTS))
+		name = x86_cap_flags[bit];
+	else if (likely(word < NCAPINTS + NBUGINTS))
+		name = x86_bug_flags[bit - 32 * NCAPINTS];
+
+	if (name)
+		return name;
+
+	snprintf(buf, 16, "%u:%u", word, bit & 31);
+	return buf;
+}
+
 /*
  * This does the hard work of actually picking apart the CPU stuff...
  */
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index 146f6f8b0650..7fad18e7d2eb 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -2,6 +2,7 @@
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/cpu.h>
 #include <asm/cpufeature.h>
 
 struct cpuid_dep {
@@ -156,21 +157,6 @@ void setup_clear_cpu_cap(unsigned int feature)
 	do_clear_cpu_cap(NULL, feature);
 }
 
-/*
- * Return the feature "name" if available, otherwise return
- * the X86_FEATURE_* numerals to make it easier to identify
- * the feature.
- */
-static const char *x86_feature_name(unsigned int feature, char *buf)
-{
-	if (x86_cap_flags[feature])
-		return x86_cap_flags[feature];
-
-	snprintf(buf, 16, "%d*32+%2d", feature / 32, feature % 32);
-
-	return buf;
-}
-
 void check_cpufeature_deps(struct cpuinfo_x86 *c)
 {
 	char feature_buf[16], depends_buf[16];
@@ -185,8 +171,8 @@ void check_cpufeature_deps(struct cpuinfo_x86 *c)
 			 */
 			pr_warn_once("x86 CPU feature dependency check failure: CPU%d has '%s' enabled but '%s' disabled. Kernel might be fine, but no guarantees.\n",
 				     smp_processor_id(),
-				     x86_feature_name(d->feature, feature_buf),
-				     x86_feature_name(d->depends, depends_buf));
+				     x86_cap_name(d->feature, feature_buf),
+				     x86_cap_name(d->depends, depends_buf));
 		}
 	}
 }
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 8239cd95a005..acd3f0f4867a 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -233,4 +233,6 @@ int arch_get_indir_br_lp_status(struct task_struct *t, unsigned long __user *sta
 int arch_set_indir_br_lp_status(struct task_struct *t, unsigned long status);
 int arch_lock_indir_br_lp_status(struct task_struct *t, unsigned long status);
 
+const char *x86_cap_name(unsigned int bit, char *buf);
+
 #endif /* _LINUX_CPU_H_ */
-- 
2.53.0