kasan: implement stack ring for tag-based modes

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 number of entries in the stack ring is fixed in this patch, but one of
the following patches adds a command-line argument to control it.

[andreyknvl@google.com: initialize read-write lock in stack ring]
Link: https://lkml.kernel.org/r/576182d194e27531e8090bad809e4136953895f4.1663700262.git.andreyknvl@google.com
Link: https://lkml.kernel.org/r/692de14b6b6a1bc817fd55e4ad92fc1f83c1ab59.1662411799.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Peter Collingbourne <pcc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 7df107d..cfff811 100644 (file)
--- 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>
@@ -233,6 +234,26 @@ struct kasan_free_meta {
 
 #endif /* CONFIG_KASAN_GENERIC */
 
+#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
+
+struct kasan_stack_ring_entry {
+       void *ptr;
+       size_t size;
+       u32 pid;
+       depot_stack_handle_t stack;
+       bool is_free;
+};
+
+#define KASAN_STACK_RING_SIZE (32 << 10)
+
+struct kasan_stack_ring {
+       rwlock_t lock;
+       atomic64_t pos;
+       struct kasan_stack_ring_entry entries[KASAN_STACK_RING_SIZE];
+};
+
+#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 5cbac2c..1b78136 100644 (file)
--- 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 +28,72 @@ static const char *get_bug_type(struct kasan_report_info *info)
 
 void kasan_complete_mode_report_info(struct kasan_report_info *info)
 {
+       unsigned long flags;
+       u64 pos;
+       struct kasan_stack_ring_entry *entry;
+       void *ptr;
+       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;
+       }
+
+       write_lock_irqsave(&stack_ring.lock, flags);
+
+       pos = atomic64_read(&stack_ring.pos);
+
+       /*
+        * The loop below tries to find stack ring entries relevant to the
+        * buggy object. This is a best-effort process.
+        *
+        * First, another object with the same tag can be allocated in place of
+        * the buggy object. Also, since the number of entries is limited, the
+        * entries relevant to the buggy object can be overwritten.
+        */
+
+       for (u64 i = pos - 1; i != pos - 1 - KASAN_STACK_RING_SIZE; i--) {
+               if (alloc_found && free_found)
+                       break;
+
+               entry = &stack_ring.entries[i % KASAN_STACK_RING_SIZE];
+
+               /* Paired with smp_store_release() in save_stack_info(). */
+               ptr = (void *)smp_load_acquire(&entry->ptr);
+
+               if (kasan_reset_tag(ptr) != info->object ||
+                   get_tag(ptr) != get_tag(info->access_addr))
+                       continue;
+
+               pid = READ_ONCE(entry->pid);
+               stack = READ_ONCE(entry->stack);
+               is_free = READ_ONCE(entry->is_free);
+
+               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;
+               }
+       }
+
+       write_unlock_irqrestore(&stack_ring.lock, flags);
 }

diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index 39a0481..a0524e0 100644 (file)
--- 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 +17,62 @@
 #include <linux/types.h>
 
 #include "kasan.h"
+#include "../slab.h"
+
+/* Non-zero, as initial pointer values are 0. */
+#define STACK_RING_BUSY_PTR ((void *)1)
+
+struct kasan_stack_ring stack_ring = {
+       .lock = __RW_LOCK_UNLOCKED(stack_ring.lock)
+};
+
+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;
+       u64 pos;
+       struct kasan_stack_ring_entry *entry;
+       void *old_ptr;
+
+       stack = kasan_save_stack(gfp_flags, true);
+
+       /*
+        * Prevent save_stack_info() from modifying stack ring
+        * when kasan_complete_mode_report_info() is walking it.
+        */
+       read_lock_irqsave(&stack_ring.lock, flags);
+
+next:
+       pos = atomic64_fetch_add(1, &stack_ring.pos);
+       entry = &stack_ring.entries[pos % KASAN_STACK_RING_SIZE];
+
+       /* Detect stack ring entry slots that are being written to. */
+       old_ptr = READ_ONCE(entry->ptr);
+       if (old_ptr == STACK_RING_BUSY_PTR)
+               goto next; /* Busy slot. */
+       if (!try_cmpxchg(&entry->ptr, &old_ptr, STACK_RING_BUSY_PTR))
+               goto next; /* Busy slot. */
+
+       WRITE_ONCE(entry->size, cache->object_size);
+       WRITE_ONCE(entry->pid, current->pid);
+       WRITE_ONCE(entry->stack, stack);
+       WRITE_ONCE(entry->is_free, is_free);
+
+       /*
+        * Paired with smp_load_acquire() in kasan_complete_mode_report_info().
+        */
+       smp_store_release(&entry->ptr, (s64)object);
+
+       read_unlock_irqrestore(&stack_ring.lock, flags);
+}
 
 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);
 }