[PATCH v2 19/19] kasan: use stack_depot_put for tag-based modes

andrey.konovalov
2023-09-13T17:18:50Z

From: Andrey Konovalov <andreyknvl@google.com>

Make tag-based KASAN modes to 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.

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/report_tags.c | 1 +
mm/kasan/tags.c | 10 ++++++++--
2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/report_tags.c b/mm/kasan/report_tags.c
index 98c238ba3545..55154743f915 100644
--- a/mm/kasan/report_tags.c
+++ b/mm/kasan/report_tags.c
@@ -7,6 +7,7 @@
#include <linux/atomic.h>

#include "kasan.h"
+#include "../slab.h"

extern struct kasan_stack_ring stack_ring;

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