1 files changed, 107 insertions, 0 deletions
diff --git a/mm/kasan/report_tags.c b/mm/kasan/report_tags.c
new file mode 100644
index 000000000000..d15f8f580e2c
--- /dev/null
+++ b/mm/kasan/report_tags.c
@@ -0,0 +1,107 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2014 Samsung Electronics Co., Ltd.
+ * Copyright (c) 2020 Google, Inc.
+ */
+
+#include <linux/atomic.h>
+
+#include "kasan.h"
+#include "../slab.h"
+
+extern struct kasan_stack_ring stack_ring;
+
+static const char *get_common_bug_type(struct kasan_report_info *info)
+{
+	/*
+	 * If access_size is a negative number, then it has reason to be
+	 * defined as out-of-bounds bug type.
+	 *
+	 * Casting negative numbers to size_t would indeed turn up as
+	 * a large size_t and its value will be larger than ULONG_MAX/2,
+	 * so that this can qualify as out-of-bounds.
+	 */
+	if (info->access_addr + info->access_size < info->access_addr)
+		return "out-of-bounds";
+
+	return "invalid-access";
+}
+
+void kasan_complete_mode_report_info(struct kasan_report_info *info)
+{
+	unsigned long flags;
+	u64 pos;
+	struct kasan_stack_ring_entry *entry;
+	bool alloc_found = false, free_found = false;
+
+	if ((!info->cache || !info->object) && !info->bug_type) {
+		info->bug_type = get_common_bug_type(info);
+		return;
+	}
+
+	write_lock_irqsave(&stack_ring.lock, flags);
+
+	pos = atomic64_read(&stack_ring.pos);
+
+	/*
+	 * The loop below tries to find stack ring entries relevant to the
+	 * buggy object. This is a best-effort process.
+	 *
+	 * First, another object with the same tag can be allocated in place of
+	 * the buggy object. Also, since the number of entries is limited, the
+	 * entries relevant to the buggy object can be overwritten.
+	 */
+
+	for (u64 i = pos - 1; i != pos - 1 - stack_ring.size; i--) {
+		if (alloc_found && free_found)
+			break;
+
+		entry = &stack_ring.entries[i % stack_ring.size];
+
+		if (kasan_reset_tag(entry->ptr) != info->object ||
+		    get_tag(entry->ptr) != get_tag(info->access_addr) ||
+		    info->cache->object_size != entry->size)
+			continue;
+
+		if (entry->is_free) {
+			/*
+			 * Second free of the same object.
+			 * Give up on trying to find the alloc entry.
+			 */
+			if (free_found)
+				break;
+
+			memcpy(&info->free_track, &entry->track,
+			       sizeof(info->free_track));
+			free_found = true;
+
+			/*
+			 * If a free entry is found first, the bug is likely
+			 * a use-after-free.
+			 */
+			if (!info->bug_type)
+				info->bug_type = "slab-use-after-free";
+		} else {
+			/* Second alloc of the same object. Give up. */
+			if (alloc_found)
+				break;
+
+			memcpy(&info->alloc_track, &entry->track,
+			       sizeof(info->alloc_track));
+			alloc_found = true;
+
+			/*
+			 * If an alloc entry is found first, the bug is likely
+			 * an out-of-bounds.
+			 */
+			if (!info->bug_type)
+				info->bug_type = "slab-out-of-bounds";
+		}
+	}
+
+	write_unlock_irqrestore(&stack_ring.lock, flags);
+
+	/* Assign the common bug type if no entries were found. */
+	if (!info->bug_type)
+		info->bug_type = get_common_bug_type(info);
+}