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