[PATCH RFC] kasan: use stack_depot_put for Generic mode

[andrey.konovalov@linux.dev]

From: Andrey Konovalov <andreyknvl@google.com>

Evict alloc/free stack traces from the stack depot for Generic KASAN
once they are evicted from the quaratine.

For auxiliary stack traces, evict the oldest stack trace once a new one
is saved (KASAN only keeps references to the last two).

Also evict all save stack traces on krealloc.

To avoid double-evicting and mis-evicting stack traces (in case KASAN's
metadata was corrupted), reset KASAN's per-object metadata that stores
stack depot handles when the object is initialized and when it's evicted
from the quarantine.

Note that stack_depot_put is no-op of the handle is 0.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

---

This goes on top of the "stackdepot: allow evicting stack traces" series.
I'll mail the patches all together after the merge window.
---
 mm/kasan/common.c     |  3 ++-
 mm/kasan/generic.c    | 22 ++++++++++++++++++----
 mm/kasan/quarantine.c | 26 ++++++++++++++++++++------
 3 files changed, 40 insertions(+), 11 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 825a0240ec02..b5d8bd26fced 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -50,7 +50,8 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags, depot_flags_t depot_flags)
 void kasan_set_track(struct kasan_track *track, gfp_t flags)
 {
 	track->pid = current->pid;
-	track->stack = kasan_save_stack(flags, STACK_DEPOT_FLAG_CAN_ALLOC);
+	track->stack = kasan_save_stack(flags,
+			STACK_DEPOT_FLAG_CAN_ALLOC | STACK_DEPOT_FLAG_GET);
 }
 
 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 5d168c9afb32..50cc519e23f4 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -449,10 +449,14 @@ struct kasan_free_meta *kasan_get_free_meta(struct kmem_cache *cache,
 void kasan_init_object_meta(struct kmem_cache *cache, const void *object)
 {
 	struct kasan_alloc_meta *alloc_meta;
+	struct kasan_free_meta *free_meta;
 
 	alloc_meta = kasan_get_alloc_meta(cache, object);
 	if (alloc_meta)
 		__memset(alloc_meta, 0, sizeof(*alloc_meta));
+	free_meta = kasan_get_free_meta(cache, object);
+	if (free_meta)
+		__memset(free_meta, 0, sizeof(*free_meta));
 }
 
 size_t kasan_metadata_size(struct kmem_cache *cache, bool in_object)
@@ -489,18 +493,20 @@ 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]);
 	alloc_meta->aux_stack[1] = alloc_meta->aux_stack[0];
 	alloc_meta->aux_stack[0] = kasan_save_stack(0, depot_flags);
 }
 
 void kasan_record_aux_stack(void *addr)
 {
-	return __kasan_record_aux_stack(addr, STACK_DEPOT_FLAG_CAN_ALLOC);
+	return __kasan_record_aux_stack(addr,
+			STACK_DEPOT_FLAG_CAN_ALLOC | STACK_DEPOT_FLAG_GET);
 }
 
 void kasan_record_aux_stack_noalloc(void *addr)
 {
-	return __kasan_record_aux_stack(addr, 0);
+	return __kasan_record_aux_stack(addr, STACK_DEPOT_FLAG_GET);
 }
 
 void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
@@ -508,8 +514,16 @@ void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
 	struct kasan_alloc_meta *alloc_meta;
 
 	alloc_meta = kasan_get_alloc_meta(cache, object);
-	if (alloc_meta)
-		kasan_set_track(&alloc_meta->alloc_track, flags);
+	if (!alloc_meta)
+		return;
+
+	/* Evict previous stack traces (might exist for krealloc). */
+	stack_depot_put(alloc_meta->alloc_track.stack);
+	stack_depot_put(alloc_meta->aux_stack[0]);
+	stack_depot_put(alloc_meta->aux_stack[1]);
+	__memset(alloc_meta, 0, sizeof(*alloc_meta));
+
+	kasan_set_track(&alloc_meta->alloc_track, flags);
 }
 
 void kasan_save_free_info(struct kmem_cache *cache, void *object)
diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 152dca73f398..37fb0e3f5876 100644
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -141,11 +141,22 @@ static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache)
 static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
 {
 	void *object = qlink_to_object(qlink, cache);
-	struct kasan_free_meta *meta = kasan_get_free_meta(cache, object);
+	struct kasan_alloc_meta *alloc_meta = kasan_get_alloc_meta(cache, object);
+	struct kasan_free_meta *free_meta = kasan_get_free_meta(cache, object);
 	unsigned long flags;
 
-	if (IS_ENABLED(CONFIG_SLAB))
-		local_irq_save(flags);
+	if (alloc_meta) {
+		stack_depot_put(alloc_meta->alloc_track.stack);
+		stack_depot_put(alloc_meta->aux_stack[0]);
+		stack_depot_put(alloc_meta->aux_stack[1]);
+		__memset(alloc_meta, 0, sizeof(*alloc_meta));
+	}
+
+	if (free_meta &&
+	    *(u8 *)kasan_mem_to_shadow(object) == KASAN_SLAB_FREETRACK) {
+		stack_depot_put(free_meta->free_track.stack);
+		free_meta->free_track.stack = 0;
+	}
 
 	/*
 	 * If init_on_free is enabled and KASAN's free metadata is stored in
@@ -155,14 +166,17 @@ static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
 	 */
 	if (slab_want_init_on_free(cache) &&
 	    cache->kasan_info.free_meta_offset == 0)
-		memzero_explicit(meta, sizeof(*meta));
+		memzero_explicit(free_meta, sizeof(*free_meta));
 
 	/*
-	 * As the object now gets freed from the quarantine, assume that its
-	 * free track is no longer valid.
+	 * As the object now gets freed from the quarantine,
+	 * take note that its free track is no longer exists.
 	 */
 	*(u8 *)kasan_mem_to_shadow(object) = KASAN_SLAB_FREE;
 
+	if (IS_ENABLED(CONFIG_SLAB))
+		local_irq_save(flags);
+
 	___cache_free(cache, object, _THIS_IP_);
 
 	if (IS_ENABLED(CONFIG_SLAB))
-- 
2.25.1