[PATCH v5 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.

Add a helper that verifies the feature string in filter_cpuid_features()
is non-zero, and also cleans up the open coded paths mentioned above.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
---
 arch/x86/kernel/cpu/common.c     | 25 ++++++++++++++++++++-----
 arch/x86/kernel/cpu/cpuid-deps.c | 21 +++------------------
 include/linux/cpu.h              |  2 ++
 3 files changed, 25 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 8d12c5722245..7aede0760ebc 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -697,7 +697,7 @@ 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), df->level);
 	}
 }
 
@@ -1651,10 +1651,7 @@ 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));
 
 				taint++;
 			}
@@ -1972,6 +1969,24 @@ static void generic_identify(struct cpuinfo_x86 *c)
 #endif
 }
 
+const char *x86_cap_name(unsigned int bit)
+{
+	unsigned int word = bit >> 5;
+	static char undef_buf[16];
+	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(undef_buf, sizeof(undef_buf), "%u:%u", word, bit & 31);
+	return undef_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..1106a5476dca 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 {
@@ -156,24 +157,8 @@ 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];
 	const struct cpuid_dep *d;
 
 	for (d = cpuid_deps; d->feature; d++) {
@@ -185,8 +170,8 @@ 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),
+				     x86_cap_name(d->depends));
 		}
 	}
 }
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 487b3bf2e1ea..8b2176561f29 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -229,4 +229,6 @@ static inline bool cpu_attack_vector_mitigated(enum cpu_attack_vectors v)
 #define smt_mitigations SMT_MITIGATIONS_OFF
 #endif
 
+const char *x86_cap_name(unsigned int bit);
+
 #endif /* _LINUX_CPU_H_ */
-- 
2.53.0