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/* SPDX-License-Identifier: GPL-2.0 */
/*
* Kernel Electric-Fence (KFENCE). For more info please see
* Documentation/dev-tools/kfence.rst.
*
* Copyright (C) 2020, Google LLC.
*/
#ifndef MM_KFENCE_KFENCE_H
#define MM_KFENCE_KFENCE_H
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/types.h>
#include "../slab.h" /* for struct kmem_cache */
/*
* Get the canary byte pattern for @addr. Use a pattern that varies based on the
* lower 3 bits of the address, to detect memory corruptions with higher
* probability, where similar constants are used.
*/
#define KFENCE_CANARY_PATTERN_U8(addr) ((u8)0xaa ^ (u8)((unsigned long)(addr) & 0x7))
/*
* Define a continuous 8-byte canary starting from a multiple of 8. The canary
* of each byte is only related to the lowest three bits of its address, so the
* canary of every 8 bytes is the same. 64-bit memory can be filled and checked
* at a time instead of byte by byte to improve performance.
*/
#define KFENCE_CANARY_PATTERN_U64 ((u64)0xaaaaaaaaaaaaaaaa ^ (u64)(le64_to_cpu(0x0706050403020100)))
/* Maximum stack depth for reports. */
#define KFENCE_STACK_DEPTH 64
/* KFENCE object states. */
enum kfence_object_state {
KFENCE_OBJECT_UNUSED, /* Object is unused. */
KFENCE_OBJECT_ALLOCATED, /* Object is currently allocated. */
KFENCE_OBJECT_FREED, /* Object was allocated, and then freed. */
};
/* Alloc/free tracking information. */
struct kfence_track {
pid_t pid;
int cpu;
u64 ts_nsec;
int num_stack_entries;
unsigned long stack_entries[KFENCE_STACK_DEPTH];
};
/* KFENCE metadata per guarded allocation. */
struct kfence_metadata {
struct list_head list; /* Freelist node; access under kfence_freelist_lock. */
struct rcu_head rcu_head; /* For delayed freeing. */
/*
* Lock protecting below data; to ensure consistency of the below data,
* since the following may execute concurrently: __kfence_alloc(),
* __kfence_free(), kfence_handle_page_fault(). However, note that we
* cannot grab the same metadata off the freelist twice, and multiple
* __kfence_alloc() cannot run concurrently on the same metadata.
*/
raw_spinlock_t lock;
/* The current state of the object; see above. */
enum kfence_object_state state;
/*
* Allocated object address; cannot be calculated from size, because of
* alignment requirements.
*
* Invariant: ALIGN_DOWN(addr, PAGE_SIZE) is constant.
*/
unsigned long addr;
/*
* The size of the original allocation.
*/
size_t size;
/*
* The kmem_cache cache of the last allocation; NULL if never allocated
* or the cache has already been destroyed.
*/
struct kmem_cache *cache;
/*
* In case of an invalid access, the page that was unprotected; we
* optimistically only store one address.
*/
unsigned long unprotected_page;
/* Allocation and free stack information. */
struct kfence_track alloc_track;
struct kfence_track free_track;
/* For updating alloc_covered on frees. */
u32 alloc_stack_hash;
#ifdef CONFIG_MEMCG
struct obj_cgroup *objcg;
#endif
};
#define KFENCE_METADATA_SIZE PAGE_ALIGN(sizeof(struct kfence_metadata) * \
CONFIG_KFENCE_NUM_OBJECTS)
extern struct kfence_metadata *kfence_metadata;
static inline struct kfence_metadata *addr_to_metadata(unsigned long addr)
{
long index;
/* The checks do not affect performance; only called from slow-paths. */
if (!is_kfence_address((void *)addr))
return NULL;
/*
* May be an invalid index if called with an address at the edge of
* __kfence_pool, in which case we would report an "invalid access"
* error.
*/
index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1;
if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS)
return NULL;
return &kfence_metadata[index];
}
/* KFENCE error types for report generation. */
enum kfence_error_type {
KFENCE_ERROR_OOB, /* Detected a out-of-bounds access. */
KFENCE_ERROR_UAF, /* Detected a use-after-free access. */
KFENCE_ERROR_CORRUPTION, /* Detected a memory corruption on free. */
KFENCE_ERROR_INVALID, /* Invalid access of unknown type. */
KFENCE_ERROR_INVALID_FREE, /* Invalid free. */
};
void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
const struct kfence_metadata *meta, enum kfence_error_type type);
void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta);
#endif /* MM_KFENCE_KFENCE_H */
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