From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Implement storing stack depot handles for alloc/free stack traces for
slab objects for the tag-based KASAN modes in a ring buffer.
This ring buffer is referred to as the stack ring.
On each alloc/free of a slab object, the tagged address of the object and
the current stack trace are recorded in the stack ring.
On each bug report, if the accessed address belongs to a slab object, the
stack ring is scanned for matching entries. The newest entries are used to
print the alloc/free stack traces in the report: one entry for alloc and
one for free.
The ring buffer is lock-free.
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
The number of entries in the stack ring is fixed in this version of the
patch. We could either implement it as a config option or a command-line
argument. I tilt towards the latter option and will implement it in v2
unless there are objections.
---
mm/kasan/kasan.h | 20 ++++++++++++++
mm/kasan/report_tags.c | 61 ++++++++++++++++++++++++++++++++++++++++++
mm/kasan/tags.c | 30 +++++++++++++++++++++
3 files changed, 111 insertions(+)
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index c51cea31ced0..da9a3c56ef4b 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -2,6 +2,7 @@
#ifndef __MM_KASAN_KASAN_H
#define __MM_KASAN_KASAN_H
+#include <linux/atomic.h>
#include <linux/kasan.h>
#include <linux/kasan-tags.h>
#include <linux/kfence.h>
@@ -227,6 +228,25 @@ struct kasan_free_meta {
#endif /* CONFIG_KASAN_GENERIC */
+#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
+
+struct kasan_stack_ring_entry {
+ atomic64_t ptr; /* void * */
+ atomic64_t size; /* size_t */
+ atomic_t pid; /* u32 */
+ atomic_t stack; /* depot_stack_handle_t */
+ atomic_t is_free; /* bool */
+};
+
+#define KASAN_STACK_RING_ENTRIES (32 << 10)
+
+struct kasan_stack_ring {
+ atomic64_t pos;
+ struct kasan_stack_ring_entry entries[KASAN_STACK_RING_ENTRIES];
+};
+
+#endif /* CONFIG_KASAN_SW_TAGS || CONFIG_KASAN_HW_TAGS */
+
#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
/* Used in KUnit-compatible KASAN tests. */
struct kunit_kasan_status {
diff --git a/mm/kasan/report_tags.c b/mm/kasan/report_tags.c
index 5cbac2cdb177..21911d1883d3 100644
--- a/mm/kasan/report_tags.c
+++ b/mm/kasan/report_tags.c
@@ -4,8 +4,12 @@
* Copyright (c) 2020 Google, Inc.
*/
+#include <linux/atomic.h>
+
#include "kasan.h"
+extern struct kasan_stack_ring stack_ring;
+
static const char *get_bug_type(struct kasan_report_info *info)
{
/*
@@ -24,5 +28,62 @@ static const char *get_bug_type(struct kasan_report_info *info)
void kasan_complete_mode_report_info(struct kasan_report_info *info)
{
+ u64 pos;
+ struct kasan_stack_ring_entry *entry;
+ void *object;
+ u32 pid;
+ depot_stack_handle_t stack;
+ bool is_free;
+ bool alloc_found = false, free_found = false;
+
info->bug_type = get_bug_type(info);
+
+ if (!info->cache || !info->object)
+ return;
+
+ pos = atomic64_read(&stack_ring.pos);
+
+ for (u64 i = pos - 1; i != pos - 1 - KASAN_STACK_RING_ENTRIES; i--) {
+ if (alloc_found && free_found)
+ break;
+
+ entry = &stack_ring.entries[i % KASAN_STACK_RING_ENTRIES];
+
+ /* Paired with atomic64_set_release() in save_stack_info(). */
+ object = (void *)atomic64_read_acquire(&entry->ptr);
+
+ if (kasan_reset_tag(object) != info->object ||
+ get_tag(object) != get_tag(info->access_addr))
+ continue;
+
+ pid = atomic_read(&entry->pid);
+ stack = atomic_read(&entry->stack);
+ is_free = atomic_read(&entry->is_free);
+
+ /* Try detecting if the entry was changed while being read. */
+ smp_mb();
+ if (object != (void *)atomic64_read(&entry->ptr))
+ continue;
+
+ if (is_free) {
+ /*
+ * Second free of the same object.
+ * Give up on trying to find the alloc entry.
+ */
+ if (free_found)
+ break;
+
+ info->free_track.pid = pid;
+ info->free_track.stack = stack;
+ free_found = true;
+ } else {
+ /* Second alloc of the same object. Give up. */
+ if (alloc_found)
+ break;
+
+ info->alloc_track.pid = pid;
+ info->alloc_track.stack = stack;
+ alloc_found = true;
+ }
+ }
}
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index 39a0481e5228..286011307695 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -6,6 +6,7 @@
* Copyright (c) 2020 Google, Inc.
*/
+#include <linux/atomic.h>
#include <linux/init.h>
#include <linux/kasan.h>
#include <linux/kernel.h>
@@ -16,11 +17,40 @@
#include <linux/types.h>
#include "kasan.h"
+#include "../slab.h"
+
+struct kasan_stack_ring stack_ring;
+
+void save_stack_info(struct kmem_cache *cache, void *object,
+ gfp_t flags, bool is_free)
+{
+ u64 pos;
+ struct kasan_stack_ring_entry *entry;
+ depot_stack_handle_t stack;
+
+ stack = kasan_save_stack(flags, true);
+
+ pos = atomic64_fetch_add(1, &stack_ring.pos);
+ entry = &stack_ring.entries[pos % KASAN_STACK_RING_ENTRIES];
+
+ atomic64_set(&entry->size, cache->object_size);
+ atomic_set(&entry->pid, current->pid);
+ atomic_set(&entry->stack, stack);
+ atomic_set(&entry->is_free, is_free);
+
+ /*
+ * Paired with atomic64_read_acquire() in
+ * kasan_complete_mode_report_info().
+ */
+ atomic64_set_release(&entry->ptr, (s64)object);
+}
void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
{
+ save_stack_info(cache, object, flags, false);
}
void kasan_save_free_info(struct kmem_cache *cache, void *object)
{
+ save_stack_info(cache, object, GFP_NOWAIT, true);
}
--
2.25.1
