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From:   andrey.konovalov@linux.dev
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Andrey Konovalov <andreyknvl@gmail.com>,
        Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Vlastimil Babka <vbabka@suse.cz>, kasan-dev@googlegroups.com,
        Evgenii Stepanov <eugenis@google.com>,
        Oscar Salvador <osalvador@suse.de>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH v4 20/22] kasan: use stack_depot_put for tag-based modes
Date:   Mon, 20 Nov 2023 18:47:18 +0100
Message-Id: <b4773e5c1b0b9df6826ec0b65c1923feadfa78e5.1700502145.git.andreyknvl@google.com>
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From: Andrey Konovalov <andreyknvl@google.com>

Make tag-based KASAN modes evict stack traces from the stack depot once
they are evicted from the stack ring.

Internally, pass STACK_DEPOT_FLAG_GET to stack_depot_save_flags (via
kasan_save_stack) to increment the refcount when saving a new entry
to stack ring and call stack_depot_put when removing an entry from
stack ring.

Reviewed-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

---

Changes v1->v2:
- Adapt to the stack depot API change.
- Drop READ_ONCE when reading entry->stack.
---
 mm/kasan/tags.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index b6c017e670d8..739ae997463d 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -97,12 +97,13 @@ static void save_stack_info(struct kmem_cache *cache, void *object,
 			gfp_t gfp_flags, bool is_free)
 {
 	unsigned long flags;
-	depot_stack_handle_t stack;
+	depot_stack_handle_t stack, old_stack;
 	u64 pos;
 	struct kasan_stack_ring_entry *entry;
 	void *old_ptr;
 
-	stack = kasan_save_stack(gfp_flags, STACK_DEPOT_FLAG_CAN_ALLOC);
+	stack = kasan_save_stack(gfp_flags,
+			STACK_DEPOT_FLAG_CAN_ALLOC | STACK_DEPOT_FLAG_GET);
 
 	/*
 	 * Prevent save_stack_info() from modifying stack ring
@@ -121,6 +122,8 @@ static void save_stack_info(struct kmem_cache *cache, void *object,
 	if (!try_cmpxchg(&entry->ptr, &old_ptr, STACK_RING_BUSY_PTR))
 		goto next; /* Busy slot. */
 
+	old_stack = entry->stack;
+
 	entry->size = cache->object_size;
 	entry->pid = current->pid;
 	entry->stack = stack;
@@ -129,6 +132,9 @@ static void save_stack_info(struct kmem_cache *cache, void *object,
 	entry->ptr = object;
 
 	read_unlock_irqrestore(&stack_ring.lock, flags);
+
+	if (old_stack)
+		stack_depot_put(old_stack);
 }
 
 void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
-- 
2.25.1