arm64: cacheinfo: Avoid out-of-bounds write to cacheinfo array

jira VULN-54126
cve CVE-2025-21785
commit-author Radu Rendec <[email protected]>
commit 875d742

The loop that detects/populates cache information already has a bounds
check on the array size but does not account for cache levels with
separate data/instructions cache. Fix this by incrementing the index
for any populated leaf (instead of any populated level).

Fixes: 5d425c1 ("arm64: kernel: add support for cpu cache information")

	Signed-off-by: Radu Rendec <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
	Signed-off-by: Will Deacon <[email protected]>
(cherry picked from commit 875d742)
	Signed-off-by: Marcin Wcisło <[email protected]>

Author: pvts-mat

arch/arm64/kernel/cacheinfo.c

@@ -98,16 +98,18 @@ static int __populate_cache_leaves(unsigned int cpu)
 	unsigned int level, idx;
 	enum cache_type type;
 	struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
-	struct cacheinfo *this_leaf = this_cpu_ci->info_list;
+	struct cacheinfo *infos = this_cpu_ci->info_list;
 
 	for (idx = 0, level = 1; level <= this_cpu_ci->num_levels &&
-	     idx < this_cpu_ci->num_leaves; idx++, level++) {
+	     idx < this_cpu_ci->num_leaves; level++) {
 		type = get_cache_type(level);
 		if (type == CACHE_TYPE_SEPARATE) {
-			ci_leaf_init(this_leaf++, CACHE_TYPE_DATA, level);
-			ci_leaf_init(this_leaf++, CACHE_TYPE_INST, level);
+			if (idx + 1 >= this_cpu_ci->num_leaves)
+				break;
+			ci_leaf_init(&infos[idx++], CACHE_TYPE_DATA, level);
+			ci_leaf_init(&infos[idx++], CACHE_TYPE_INST, level);
 		} else {
-			ci_leaf_init(this_leaf++, type, level);
+			ci_leaf_init(&infos[idx++], type, level);
 		}
 	}
 	return 0;