tools/x86/kcpuid: Consolidate index validity checks

Let index_to_cpuid_range() return a CPUID range only if the passed index
is within a CPUID range's maximum supported function on the CPU.
Returning a CPUID range that is invalid on the CPU for the passed index
does not make sense.

This also avoids repeating the "function index is within CPUID range"
checks, both at setup_cpuid_range() and index_to_func().

Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20250324142042.29010-14-darwi@linutronix.de

1 files changed, 9 insertions, 12 deletions

diff --git a/tools/arch/x86/kcpuid/kcpuid.c b/tools/arch/x86/kcpuid/kcpuid.c
index 1f48de343d4d..ac3d36bef85f 100644
--- a/tools/arch/x86/kcpuid/kcpuid.c
+++ b/tools/arch/x86/kcpuid/kcpuid.c
@@ -101,10 +101,12 @@ static char *range_to_str(struct cpuid_range *range)
 
 struct cpuid_range *index_to_cpuid_range(u32 index)
 {
+	u32 func_idx = index & CPUID_FUNCTION_MASK;
+	u32 range_idx = index & CPUID_INDEX_MASK;
 	struct cpuid_range *range;
 
 	for_each_cpuid_range(range) {
-		if (range->index == (index & CPUID_INDEX_MASK))
+		if (range->index == range_idx && (u32)range->nr > func_idx)
 			return range;
 	}
 
@@ -331,17 +333,16 @@ static void parse_line(char *line)
 	/* index/main-leaf */
 	index = strtoull(tokens[0], NULL, 0);
 
-	/* Skip line parsing if it's not covered by known ranges */
+	/*
+	 * Skip line parsing if the index is not covered by known-valid
+	 * CPUID ranges on this CPU.
+	 */
 	range = index_to_cpuid_range(index);
 	if (!range)
 		return;
 
-	/* Skip line parsing for non-existing indexes */
-	index &= CPUID_FUNCTION_MASK;
-	if ((int)index >= range->nr)
-		return;
-
 	/* Skip line parsing if the index CPUID output is all zero */
+	index &= CPUID_FUNCTION_MASK;
 	func = &range->funcs[index];
 	if (!func->nr)
 		return;
@@ -505,17 +506,13 @@ static void show_range(struct cpuid_range *range)
 
 static inline struct cpuid_func *index_to_func(u32 index)
 {
+	u32 func_idx = index & CPUID_FUNCTION_MASK;
 	struct cpuid_range *range;
-	u32 func_idx;
 
 	range = index_to_cpuid_range(index);
 	if (!range)
 		return NULL;
 
-	func_idx = index & CPUID_FUNCTION_MASK;
-	if ((func_idx + 1) > (u32)range->nr)
-		return NULL;
-
 	return &range->funcs[func_idx];
 }