251 lines
8.6 KiB
C
251 lines
8.6 KiB
C
|
/* 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 */
|