1 /* SPDX-License-Identifier: GPL-2.0 */
3 * Kernel Electric-Fence (KFENCE). Public interface for allocator and fault
4 * handler integration. For more info see Documentation/dev-tools/kfence.rst.
6 * Copyright (C) 2020, Google LLC.
9 #ifndef _LINUX_KFENCE_H
10 #define _LINUX_KFENCE_H
13 #include <linux/types.h>
18 * We allocate an even number of pages, as it simplifies calculations to map
19 * address to metadata indices; effectively, the very first page serves as an
20 * extended guard page, but otherwise has no special purpose.
22 #define KFENCE_POOL_SIZE ((CONFIG_KFENCE_NUM_OBJECTS + 1) * 2 * PAGE_SIZE)
23 extern char *__kfence_pool;
25 #ifdef CONFIG_KFENCE_STATIC_KEYS
26 #include <linux/static_key.h>
27 DECLARE_STATIC_KEY_FALSE(kfence_allocation_key);
29 #include <linux/atomic.h>
30 extern atomic_t kfence_allocation_gate;
34 * is_kfence_address() - check if an address belongs to KFENCE pool
35 * @addr: address to check
37 * Return: true or false depending on whether the address is within the KFENCE
40 * KFENCE objects live in a separate page range and are not to be intermixed
41 * with regular heap objects (e.g. KFENCE objects must never be added to the
42 * allocator freelists). Failing to do so may and will result in heap
43 * corruptions, therefore is_kfence_address() must be used to check whether
44 * an object requires specific handling.
46 * Note: This function may be used in fast-paths, and is performance critical.
47 * Future changes should take this into account; for instance, we want to avoid
48 * introducing another load and therefore need to keep KFENCE_POOL_SIZE a
49 * constant (until immediate patching support is added to the kernel).
51 static __always_inline bool is_kfence_address(const void *addr)
54 * The non-NULL check is required in case the __kfence_pool pointer was
55 * never initialized; keep it in the slow-path after the range-check.
57 return unlikely((unsigned long)((char *)addr - __kfence_pool) < KFENCE_POOL_SIZE && addr);
61 * kfence_alloc_pool() - allocate the KFENCE pool via memblock
63 void __init kfence_alloc_pool(void);
66 * kfence_init() - perform KFENCE initialization at boot time
68 * Requires that kfence_alloc_pool() was called before. This sets up the
69 * allocation gate timer, and requires that workqueues are available.
71 void __init kfence_init(void);
74 * kfence_shutdown_cache() - handle shutdown_cache() for KFENCE objects
75 * @s: cache being shut down
77 * Before shutting down a cache, one must ensure there are no remaining objects
78 * allocated from it. Because KFENCE objects are not referenced from the cache
79 * directly, we need to check them here.
81 * Note that shutdown_cache() is internal to SL*B, and kmem_cache_destroy() does
82 * not return if allocated objects still exist: it prints an error message and
83 * simply aborts destruction of a cache, leaking memory.
85 * If the only such objects are KFENCE objects, we will not leak the entire
86 * cache, but instead try to provide more useful debug info by making allocated
87 * objects "zombie allocations". Objects may then still be used or freed (which
88 * is handled gracefully), but usage will result in showing KFENCE error reports
89 * which include stack traces to the user of the object, the original allocation
90 * site, and caller to shutdown_cache().
92 void kfence_shutdown_cache(struct kmem_cache *s);
95 * Allocate a KFENCE object. Allocators must not call this function directly,
96 * use kfence_alloc() instead.
98 void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags);
101 * kfence_alloc() - allocate a KFENCE object with a low probability
102 * @s: struct kmem_cache with object requirements
103 * @size: exact size of the object to allocate (can be less than @s->size
104 * e.g. for kmalloc caches)
108 * * NULL - must proceed with allocating as usual,
109 * * non-NULL - pointer to a KFENCE object.
111 * kfence_alloc() should be inserted into the heap allocation fast path,
112 * allowing it to transparently return KFENCE-allocated objects with a low
113 * probability using a static branch (the probability is controlled by the
114 * kfence.sample_interval boot parameter).
116 static __always_inline void *kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
118 #ifdef CONFIG_KFENCE_STATIC_KEYS
119 if (static_branch_unlikely(&kfence_allocation_key))
121 if (unlikely(!atomic_read(&kfence_allocation_gate)))
123 return __kfence_alloc(s, size, flags);
128 * kfence_ksize() - get actual amount of memory allocated for a KFENCE object
129 * @addr: pointer to a heap object
132 * * 0 - not a KFENCE object, must call __ksize() instead,
133 * * non-0 - this many bytes can be accessed without causing a memory error.
135 * kfence_ksize() returns the number of bytes requested for a KFENCE object at
136 * allocation time. This number may be less than the object size of the
137 * corresponding struct kmem_cache.
139 size_t kfence_ksize(const void *addr);
142 * kfence_object_start() - find the beginning of a KFENCE object
143 * @addr: address within a KFENCE-allocated object
145 * Return: address of the beginning of the object.
147 * SL[AU]B-allocated objects are laid out within a page one by one, so it is
148 * easy to calculate the beginning of an object given a pointer inside it and
149 * the object size. The same is not true for KFENCE, which places a single
150 * object at either end of the page. This helper function is used to find the
151 * beginning of a KFENCE-allocated object.
153 void *kfence_object_start(const void *addr);
156 * __kfence_free() - release a KFENCE heap object to KFENCE pool
157 * @addr: object to be freed
159 * Requires: is_kfence_address(addr)
161 * Release a KFENCE object and mark it as freed.
163 void __kfence_free(void *addr);
166 * kfence_free() - try to release an arbitrary heap object to KFENCE pool
167 * @addr: object to be freed
170 * * false - object doesn't belong to KFENCE pool and was ignored,
171 * * true - object was released to KFENCE pool.
173 * Release a KFENCE object and mark it as freed. May be called on any object,
174 * even non-KFENCE objects, to simplify integration of the hooks into the
175 * allocator's free codepath. The allocator must check the return value to
176 * determine if it was a KFENCE object or not.
178 static __always_inline __must_check bool kfence_free(void *addr)
180 if (!is_kfence_address(addr))
187 * kfence_handle_page_fault() - perform page fault handling for KFENCE pages
188 * @addr: faulting address
189 * @is_write: is access a write
190 * @regs: current struct pt_regs (can be NULL, but shows full stack trace)
193 * * false - address outside KFENCE pool,
194 * * true - page fault handled by KFENCE, no additional handling required.
196 * A page fault inside KFENCE pool indicates a memory error, such as an
197 * out-of-bounds access, a use-after-free or an invalid memory access. In these
198 * cases KFENCE prints an error message and marks the offending page as
199 * present, so that the kernel can proceed.
201 bool __must_check kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs *regs);
203 #else /* CONFIG_KFENCE */
205 static inline bool is_kfence_address(const void *addr) { return false; }
206 static inline void kfence_alloc_pool(void) { }
207 static inline void kfence_init(void) { }
208 static inline void kfence_shutdown_cache(struct kmem_cache *s) { }
209 static inline void *kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) { return NULL; }
210 static inline size_t kfence_ksize(const void *addr) { return 0; }
211 static inline void *kfence_object_start(const void *addr) { return NULL; }
212 static inline void __kfence_free(void *addr) { }
213 static inline bool __must_check kfence_free(void *addr) { return false; }
214 static inline bool __must_check kfence_handle_page_fault(unsigned long addr, bool is_write,
215 struct pt_regs *regs)
222 #endif /* _LINUX_KFENCE_H */