1/* SPDX-License-Identifier: GPL-2.0 */
  2/*
  3 * Kernel Electric-Fence (KFENCE). For more info please see
  4 * Documentation/dev-tools/kfence.rst.
  5 *
  6 * Copyright (C) 2020, Google LLC.
  7 */
  8
  9#ifndef MM_KFENCE_KFENCE_H
 10#define MM_KFENCE_KFENCE_H
 11
 12#include <linux/mm.h>
 13#include <linux/slab.h>
 14#include <linux/spinlock.h>
 15#include <linux/types.h>
 16
 17#include "../slab.h" /* for struct kmem_cache */
 18
 19/*
 20 * Get the canary byte pattern for @addr. Use a pattern that varies based on the
 21 * lower 3 bits of the address, to detect memory corruptions with higher
 22 * probability, where similar constants are used.
 23 */
 24#define KFENCE_CANARY_PATTERN(addr) ((u8)0xaa ^ (u8)((unsigned long)(addr) & 0x7))
 25
 26/* Maximum stack depth for reports. */
 27#define KFENCE_STACK_DEPTH 64
 28
 29/* KFENCE object states. */
 30enum kfence_object_state {
 31	KFENCE_OBJECT_UNUSED,		/* Object is unused. */
 32	KFENCE_OBJECT_ALLOCATED,	/* Object is currently allocated. */
 33	KFENCE_OBJECT_FREED,		/* Object was allocated, and then freed. */
 34};
 35
 36/* Alloc/free tracking information. */
 37struct kfence_track {
 38	pid_t pid;
 39	int cpu;
 40	u64 ts_nsec;
 41	int num_stack_entries;
 42	unsigned long stack_entries[KFENCE_STACK_DEPTH];
 43};
 44
 45/* KFENCE metadata per guarded allocation. */
 46struct kfence_metadata {
 47	struct list_head list;		/* Freelist node; access under kfence_freelist_lock. */
 48	struct rcu_head rcu_head;	/* For delayed freeing. */
 49
 50	/*
 51	 * Lock protecting below data; to ensure consistency of the below data,
 52	 * since the following may execute concurrently: __kfence_alloc(),
 53	 * __kfence_free(), kfence_handle_page_fault(). However, note that we
 54	 * cannot grab the same metadata off the freelist twice, and multiple
 55	 * __kfence_alloc() cannot run concurrently on the same metadata.
 56	 */
 57	raw_spinlock_t lock;
 58
 59	/* The current state of the object; see above. */
 60	enum kfence_object_state state;
 61
 62	/*
 63	 * Allocated object address; cannot be calculated from size, because of
 64	 * alignment requirements.
 65	 *
 66	 * Invariant: ALIGN_DOWN(addr, PAGE_SIZE) is constant.
 67	 */
 68	unsigned long addr;
 69
 70	/*
 71	 * The size of the original allocation.
 72	 */
 73	size_t size;
 74
 75	/*
 76	 * The kmem_cache cache of the last allocation; NULL if never allocated
 77	 * or the cache has already been destroyed.
 78	 */
 79	struct kmem_cache *cache;
 80
 81	/*
 82	 * In case of an invalid access, the page that was unprotected; we
 83	 * optimistically only store one address.
 84	 */
 85	unsigned long unprotected_page;
 86
 87	/* Allocation and free stack information. */
 88	struct kfence_track alloc_track;
 89	struct kfence_track free_track;
 90	/* For updating alloc_covered on frees. */
 91	u32 alloc_stack_hash;
 92#ifdef CONFIG_MEMCG
 93	struct obj_cgroup *objcg;
 94#endif
 95};
 96
 97extern struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS];
 98
 99static inline struct kfence_metadata *addr_to_metadata(unsigned long addr)
100{
101	long index;
102
103	/* The checks do not affect performance; only called from slow-paths. */
104
105	if (!is_kfence_address((void *)addr))
106		return NULL;
107
108	/*
109	 * May be an invalid index if called with an address at the edge of
110	 * __kfence_pool, in which case we would report an "invalid access"
111	 * error.
112	 */
113	index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1;
114	if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS)
115		return NULL;
116
117	return &kfence_metadata[index];
118}
119
120/* KFENCE error types for report generation. */
121enum kfence_error_type {
122	KFENCE_ERROR_OOB,		/* Detected a out-of-bounds access. */
123	KFENCE_ERROR_UAF,		/* Detected a use-after-free access. */
124	KFENCE_ERROR_CORRUPTION,	/* Detected a memory corruption on free. */
125	KFENCE_ERROR_INVALID,		/* Invalid access of unknown type. */
126	KFENCE_ERROR_INVALID_FREE,	/* Invalid free. */
127};
128
129void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
130			 const struct kfence_metadata *meta, enum kfence_error_type type);
131
132void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta);
133
134#endif /* MM_KFENCE_KFENCE_H */