Commit 7bc0584e authored by Andrey Konovalov's avatar Andrey Konovalov Committed by Andrew Morton
Browse files

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: default avatarAndrey Konovalov <andreyknvl@google.com>
Acked-by: default avatarMarco 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 59e6e098

mm/kasan/kasan.h

+21 −0
Original line number Diff line number Diff line
@@ -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 {

mm/kasan/report_tags.c

+71 −0
Original line number Diff line number Diff line
@@ -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);

}

mm/kasan/tags.c

+52 −0
Original line number Diff line number Diff line
@@ -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);

}