[PATCH v3 mm 2/4] kasan: handle concurrent kasan_record_aux_stack calls

[andrey.konovalov@linux.dev]

From: Andrey Konovalov <andreyknvl@google.com>

kasan_record_aux_stack can be called concurrently on the same object.
This might lead to a race condition when rotating the saved aux stack
trace handles, which in turns leads to incorrect accounting of stack
depot handles and refcount underflows in the stack depot code.

Fix by introducing a raw spinlock to protect the aux stack trace handles
in kasan_record_aux_stack.

Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Reported-by: syzbot+186b55175d8360728234@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000784b1c060b0074a2@google.com/
Fixes: 773688a6cb24 ("kasan: use stack_depot_put for Generic mode")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

---

Changes v2->v3:
- Use raw spinlock to avoid lockdep complaints on RT kernels.

Changes v1->v2:
- Use per-object spinlock instead of a global one.
---
 mm/kasan/generic.c | 32 +++++++++++++++++++++++++++++---
 mm/kasan/kasan.h   |  8 ++++++++
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 54e20b2bc3e1..55e6b5db2cae 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -25,6 +25,7 @@
 #include <linux/sched.h>
 #include <linux/sched/task_stack.h>
 #include <linux/slab.h>
+#include <linux/spinlock.h>
 #include <linux/stackdepot.h>
 #include <linux/stacktrace.h>
 #include <linux/string.h>
@@ -471,8 +472,18 @@ void kasan_init_object_meta(struct kmem_cache *cache, const void *object)
 	struct kasan_free_meta *free_meta;
 
 	alloc_meta = kasan_get_alloc_meta(cache, object);
-	if (alloc_meta)
+	if (alloc_meta) {
 		__memset(alloc_meta, 0, sizeof(*alloc_meta));
+
+		/*
+		 * Temporarily disable KASAN bug reporting to allow instrumented
+		 * raw_spin_lock_init to access aux_lock, which resides inside
+		 * of a redzone.
+		 */
+		kasan_disable_current();
+		raw_spin_lock_init(&alloc_meta->aux_lock);
+		kasan_enable_current();
+	}
 	free_meta = kasan_get_free_meta(cache, object);
 	if (free_meta)
 		__memset(free_meta, 0, sizeof(*free_meta));
@@ -502,6 +513,8 @@ static void __kasan_record_aux_stack(void *addr, depot_flags_t depot_flags)
 	struct kmem_cache *cache;
 	struct kasan_alloc_meta *alloc_meta;
 	void *object;
+	depot_stack_handle_t new_handle, old_handle;
+	unsigned long flags;
 
 	if (is_kfence_address(addr) || !slab)
 		return;
@@ -512,9 +525,22 @@ static void __kasan_record_aux_stack(void *addr, depot_flags_t depot_flags)
 	if (!alloc_meta)
 		return;
 
-	stack_depot_put(alloc_meta->aux_stack[1]);
+	new_handle = kasan_save_stack(0, depot_flags);
+
+	/*
+	 * Temporarily disable KASAN bug reporting to allow instrumented
+	 * spinlock functions to access aux_lock, which resides inside of a
+	 * redzone.
+	 */
+	kasan_disable_current();
+	raw_spin_lock_irqsave(&alloc_meta->aux_lock, flags);
+	old_handle = alloc_meta->aux_stack[1];
 	alloc_meta->aux_stack[1] = alloc_meta->aux_stack[0];
-	alloc_meta->aux_stack[0] = kasan_save_stack(0, depot_flags);
+	alloc_meta->aux_stack[0] = new_handle;
+	raw_spin_unlock_irqrestore(&alloc_meta->aux_lock, flags);
+	kasan_enable_current();
+
+	stack_depot_put(old_handle);
 }
 
 void kasan_record_aux_stack(void *addr)
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 5e298e3ac909..69e4f5e58e33 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -6,6 +6,7 @@
 #include <linux/kasan.h>
 #include <linux/kasan-tags.h>
 #include <linux/kfence.h>
+#include <linux/spinlock.h>
 #include <linux/stackdepot.h>
 
 #if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
@@ -249,6 +250,13 @@ struct kasan_global {
 struct kasan_alloc_meta {
 	struct kasan_track alloc_track;
 	/* Free track is stored in kasan_free_meta. */
+	/*
+	 * aux_lock protects aux_stack from accesses from concurrent
+	 * kasan_record_aux_stack calls. It is a raw spinlock to avoid sleeping
+	 * on RT kernels, as kasan_record_aux_stack_noalloc can be called from
+	 * non-sleepable contexts.
+	 */
+	raw_spinlock_t aux_lock;
 	depot_stack_handle_t aux_stack[2];
 };
 
-- 
2.25.1