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>
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@ -2,6 +2,7 @@
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#ifndef __MM_KASAN_KASAN_H
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#define __MM_KASAN_KASAN_H
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#include <linux/atomic.h>
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#include <linux/kasan.h>
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#include <linux/kasan-tags.h>
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#include <linux/kfence.h>
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@ -233,6 +234,26 @@ struct kasan_free_meta {
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#endif /* CONFIG_KASAN_GENERIC */
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#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
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struct kasan_stack_ring_entry {
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void *ptr;
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size_t size;
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u32 pid;
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depot_stack_handle_t stack;
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bool is_free;
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};
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#define KASAN_STACK_RING_SIZE (32 << 10)
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struct kasan_stack_ring {
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rwlock_t lock;
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atomic64_t pos;
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struct kasan_stack_ring_entry entries[KASAN_STACK_RING_SIZE];
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};
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#endif /* CONFIG_KASAN_SW_TAGS || CONFIG_KASAN_HW_TAGS */
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#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
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/* Used in KUnit-compatible KASAN tests. */
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struct kunit_kasan_status {
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@ -4,8 +4,12 @@
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* Copyright (c) 2020 Google, Inc.
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*/
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#include <linux/atomic.h>
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#include "kasan.h"
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extern struct kasan_stack_ring stack_ring;
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static const char *get_bug_type(struct kasan_report_info *info)
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{
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/*
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@ -24,5 +28,72 @@ static const char *get_bug_type(struct kasan_report_info *info)
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void kasan_complete_mode_report_info(struct kasan_report_info *info)
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{
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unsigned long flags;
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u64 pos;
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struct kasan_stack_ring_entry *entry;
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void *ptr;
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u32 pid;
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depot_stack_handle_t stack;
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bool is_free;
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bool alloc_found = false, free_found = false;
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info->bug_type = get_bug_type(info);
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if (!info->cache || !info->object)
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return;
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}
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write_lock_irqsave(&stack_ring.lock, flags);
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pos = atomic64_read(&stack_ring.pos);
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/*
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* The loop below tries to find stack ring entries relevant to the
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* buggy object. This is a best-effort process.
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*
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* First, another object with the same tag can be allocated in place of
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* the buggy object. Also, since the number of entries is limited, the
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* entries relevant to the buggy object can be overwritten.
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*/
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for (u64 i = pos - 1; i != pos - 1 - KASAN_STACK_RING_SIZE; i--) {
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if (alloc_found && free_found)
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break;
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entry = &stack_ring.entries[i % KASAN_STACK_RING_SIZE];
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/* Paired with smp_store_release() in save_stack_info(). */
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ptr = (void *)smp_load_acquire(&entry->ptr);
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if (kasan_reset_tag(ptr) != info->object ||
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get_tag(ptr) != get_tag(info->access_addr))
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continue;
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pid = READ_ONCE(entry->pid);
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stack = READ_ONCE(entry->stack);
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is_free = READ_ONCE(entry->is_free);
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if (is_free) {
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/*
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* Second free of the same object.
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* Give up on trying to find the alloc entry.
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*/
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if (free_found)
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break;
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info->free_track.pid = pid;
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info->free_track.stack = stack;
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free_found = true;
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} else {
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/* Second alloc of the same object. Give up. */
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if (alloc_found)
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break;
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info->alloc_track.pid = pid;
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info->alloc_track.stack = stack;
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alloc_found = true;
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}
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}
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write_unlock_irqrestore(&stack_ring.lock, flags);
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}
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@ -6,6 +6,7 @@
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* Copyright (c) 2020 Google, Inc.
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*/
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#include <linux/atomic.h>
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#include <linux/init.h>
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#include <linux/kasan.h>
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#include <linux/kernel.h>
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@ -16,11 +17,62 @@
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#include <linux/types.h>
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#include "kasan.h"
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#include "../slab.h"
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/* Non-zero, as initial pointer values are 0. */
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#define STACK_RING_BUSY_PTR ((void *)1)
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struct kasan_stack_ring stack_ring = {
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.lock = __RW_LOCK_UNLOCKED(stack_ring.lock)
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};
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static void save_stack_info(struct kmem_cache *cache, void *object,
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gfp_t gfp_flags, bool is_free)
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{
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unsigned long flags;
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depot_stack_handle_t stack;
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u64 pos;
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struct kasan_stack_ring_entry *entry;
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void *old_ptr;
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stack = kasan_save_stack(gfp_flags, true);
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/*
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* Prevent save_stack_info() from modifying stack ring
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* when kasan_complete_mode_report_info() is walking it.
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*/
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read_lock_irqsave(&stack_ring.lock, flags);
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next:
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pos = atomic64_fetch_add(1, &stack_ring.pos);
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entry = &stack_ring.entries[pos % KASAN_STACK_RING_SIZE];
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/* Detect stack ring entry slots that are being written to. */
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old_ptr = READ_ONCE(entry->ptr);
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if (old_ptr == STACK_RING_BUSY_PTR)
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goto next; /* Busy slot. */
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if (!try_cmpxchg(&entry->ptr, &old_ptr, STACK_RING_BUSY_PTR))
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goto next; /* Busy slot. */
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WRITE_ONCE(entry->size, cache->object_size);
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WRITE_ONCE(entry->pid, current->pid);
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WRITE_ONCE(entry->stack, stack);
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WRITE_ONCE(entry->is_free, is_free);
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/*
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* Paired with smp_load_acquire() in kasan_complete_mode_report_info().
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*/
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smp_store_release(&entry->ptr, (s64)object);
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read_unlock_irqrestore(&stack_ring.lock, flags);
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}
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void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
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{
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save_stack_info(cache, object, flags, false);
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}
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void kasan_save_free_info(struct kmem_cache *cache, void *object)
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{
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save_stack_info(cache, object, GFP_NOWAIT, true);
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}
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