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- /* SPDX-License-Identifier: GPL-2.0 */
- /*
- * Kernel Electric-Fence (KFENCE). Public interface for allocator and fault
- * handler integration. For more info see Documentation/dev-tools/kfence.rst.
- *
- * Copyright (C) 2020, Google LLC.
- */
- #ifndef _LINUX_KFENCE_H
- #define _LINUX_KFENCE_H
- #include <linux/mm.h>
- #include <linux/types.h>
- #ifdef CONFIG_KFENCE
- #include <linux/atomic.h>
- #include <linux/static_key.h>
- extern unsigned long kfence_sample_interval;
- /*
- * We allocate an even number of pages, as it simplifies calculations to map
- * address to metadata indices; effectively, the very first page serves as an
- * extended guard page, but otherwise has no special purpose.
- */
- #define KFENCE_POOL_SIZE ((CONFIG_KFENCE_NUM_OBJECTS + 1) * 2 * PAGE_SIZE)
- extern char *__kfence_pool;
- DECLARE_STATIC_KEY_FALSE(kfence_allocation_key);
- extern atomic_t kfence_allocation_gate;
- /**
- * is_kfence_address() - check if an address belongs to KFENCE pool
- * @addr: address to check
- *
- * Return: true or false depending on whether the address is within the KFENCE
- * object range.
- *
- * KFENCE objects live in a separate page range and are not to be intermixed
- * with regular heap objects (e.g. KFENCE objects must never be added to the
- * allocator freelists). Failing to do so may and will result in heap
- * corruptions, therefore is_kfence_address() must be used to check whether
- * an object requires specific handling.
- *
- * Note: This function may be used in fast-paths, and is performance critical.
- * Future changes should take this into account; for instance, we want to avoid
- * introducing another load and therefore need to keep KFENCE_POOL_SIZE a
- * constant (until immediate patching support is added to the kernel).
- */
- static __always_inline bool is_kfence_address(const void *addr)
- {
- /*
- * The __kfence_pool != NULL check is required to deal with the case
- * where __kfence_pool == NULL && addr < KFENCE_POOL_SIZE. Keep it in
- * the slow-path after the range-check!
- */
- return unlikely((unsigned long)((char *)addr - __kfence_pool) < KFENCE_POOL_SIZE && __kfence_pool);
- }
- /**
- * kfence_alloc_pool() - allocate the KFENCE pool via memblock
- */
- void __init kfence_alloc_pool(void);
- /**
- * kfence_init() - perform KFENCE initialization at boot time
- *
- * Requires that kfence_alloc_pool() was called before. This sets up the
- * allocation gate timer, and requires that workqueues are available.
- */
- void __init kfence_init(void);
- /**
- * kfence_shutdown_cache() - handle shutdown_cache() for KFENCE objects
- * @s: cache being shut down
- *
- * Before shutting down a cache, one must ensure there are no remaining objects
- * allocated from it. Because KFENCE objects are not referenced from the cache
- * directly, we need to check them here.
- *
- * Note that shutdown_cache() is internal to SL*B, and kmem_cache_destroy() does
- * not return if allocated objects still exist: it prints an error message and
- * simply aborts destruction of a cache, leaking memory.
- *
- * If the only such objects are KFENCE objects, we will not leak the entire
- * cache, but instead try to provide more useful debug info by making allocated
- * objects "zombie allocations". Objects may then still be used or freed (which
- * is handled gracefully), but usage will result in showing KFENCE error reports
- * which include stack traces to the user of the object, the original allocation
- * site, and caller to shutdown_cache().
- */
- void kfence_shutdown_cache(struct kmem_cache *s);
- /*
- * Allocate a KFENCE object. Allocators must not call this function directly,
- * use kfence_alloc() instead.
- */
- void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags);
- /**
- * kfence_alloc() - allocate a KFENCE object with a low probability
- * @s: struct kmem_cache with object requirements
- * @size: exact size of the object to allocate (can be less than @s->size
- * e.g. for kmalloc caches)
- * @flags: GFP flags
- *
- * Return:
- * * NULL - must proceed with allocating as usual,
- * * non-NULL - pointer to a KFENCE object.
- *
- * kfence_alloc() should be inserted into the heap allocation fast path,
- * allowing it to transparently return KFENCE-allocated objects with a low
- * probability using a static branch (the probability is controlled by the
- * kfence.sample_interval boot parameter).
- */
- static __always_inline void *kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
- {
- #if defined(CONFIG_KFENCE_STATIC_KEYS) || CONFIG_KFENCE_SAMPLE_INTERVAL == 0
- if (!static_branch_unlikely(&kfence_allocation_key))
- return NULL;
- #else
- if (!static_branch_likely(&kfence_allocation_key))
- return NULL;
- #endif
- if (likely(atomic_read(&kfence_allocation_gate)))
- return NULL;
- return __kfence_alloc(s, size, flags);
- }
- /**
- * kfence_ksize() - get actual amount of memory allocated for a KFENCE object
- * @addr: pointer to a heap object
- *
- * Return:
- * * 0 - not a KFENCE object, must call __ksize() instead,
- * * non-0 - this many bytes can be accessed without causing a memory error.
- *
- * kfence_ksize() returns the number of bytes requested for a KFENCE object at
- * allocation time. This number may be less than the object size of the
- * corresponding struct kmem_cache.
- */
- size_t kfence_ksize(const void *addr);
- /**
- * kfence_object_start() - find the beginning of a KFENCE object
- * @addr: address within a KFENCE-allocated object
- *
- * Return: address of the beginning of the object.
- *
- * SL[AU]B-allocated objects are laid out within a page one by one, so it is
- * easy to calculate the beginning of an object given a pointer inside it and
- * the object size. The same is not true for KFENCE, which places a single
- * object at either end of the page. This helper function is used to find the
- * beginning of a KFENCE-allocated object.
- */
- void *kfence_object_start(const void *addr);
- /**
- * __kfence_free() - release a KFENCE heap object to KFENCE pool
- * @addr: object to be freed
- *
- * Requires: is_kfence_address(addr)
- *
- * Release a KFENCE object and mark it as freed.
- */
- void __kfence_free(void *addr);
- /**
- * kfence_free() - try to release an arbitrary heap object to KFENCE pool
- * @addr: object to be freed
- *
- * Return:
- * * false - object doesn't belong to KFENCE pool and was ignored,
- * * true - object was released to KFENCE pool.
- *
- * Release a KFENCE object and mark it as freed. May be called on any object,
- * even non-KFENCE objects, to simplify integration of the hooks into the
- * allocator's free codepath. The allocator must check the return value to
- * determine if it was a KFENCE object or not.
- */
- static __always_inline __must_check bool kfence_free(void *addr)
- {
- if (!is_kfence_address(addr))
- return false;
- __kfence_free(addr);
- return true;
- }
- /**
- * kfence_handle_page_fault() - perform page fault handling for KFENCE pages
- * @addr: faulting address
- * @is_write: is access a write
- * @regs: current struct pt_regs (can be NULL, but shows full stack trace)
- *
- * Return:
- * * false - address outside KFENCE pool,
- * * true - page fault handled by KFENCE, no additional handling required.
- *
- * A page fault inside KFENCE pool indicates a memory error, such as an
- * out-of-bounds access, a use-after-free or an invalid memory access. In these
- * cases KFENCE prints an error message and marks the offending page as
- * present, so that the kernel can proceed.
- */
- bool __must_check kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs *regs);
- #ifdef CONFIG_PRINTK
- struct kmem_obj_info;
- /**
- * __kfence_obj_info() - fill kmem_obj_info struct
- * @kpp: kmem_obj_info to be filled
- * @object: the object
- *
- * Return:
- * * false - not a KFENCE object
- * * true - a KFENCE object, filled @kpp
- *
- * Copies information to @kpp for KFENCE objects.
- */
- bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab);
- #endif
- #else /* CONFIG_KFENCE */
- static inline bool is_kfence_address(const void *addr) { return false; }
- static inline void kfence_alloc_pool(void) { }
- static inline void kfence_init(void) { }
- static inline void kfence_shutdown_cache(struct kmem_cache *s) { }
- static inline void *kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) { return NULL; }
- static inline size_t kfence_ksize(const void *addr) { return 0; }
- static inline void *kfence_object_start(const void *addr) { return NULL; }
- static inline void __kfence_free(void *addr) { }
- static inline bool __must_check kfence_free(void *addr) { return false; }
- static inline bool __must_check kfence_handle_page_fault(unsigned long addr, bool is_write,
- struct pt_regs *regs)
- {
- return false;
- }
- #ifdef CONFIG_PRINTK
- struct kmem_obj_info;
- static inline bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab)
- {
- return false;
- }
- #endif
- #endif
- #endif /* _LINUX_KFENCE_H */
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