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![Kees Cook](/assets/img/avatar_default.png)
This SLUB free list pointer obfuscation code is modified from Brad Spengler/PaX Team's code in the last public patch of grsecurity/PaX based on my understanding of the code. Changes or omissions from the original code are mine and don't reflect the original grsecurity/PaX code. This adds a per-cache random value to SLUB caches that is XORed with their freelist pointer address and value. This adds nearly zero overhead and frustrates the very common heap overflow exploitation method of overwriting freelist pointers. A recent example of the attack is written up here: http://cyseclabs.com/blog/cve-2016-6187-heap-off-by-one-exploit and there is a section dedicated to the technique the book "A Guide to Kernel Exploitation: Attacking the Core". This is based on patches by Daniel Micay, and refactored to minimize the use of #ifdef. With 200-count cycles of "hackbench -g 20 -l 1000" I saw the following run times: before: mean 10.11882499999999999995 variance .03320378329145728642 stdev .18221905304181911048 after: mean 10.12654000000000000014 variance .04700556623115577889 stdev .21680767106160192064 The difference gets lost in the noise, but if the above is to be taken literally, using CONFIG_FREELIST_HARDENED is 0.07% slower. Link: http://lkml.kernel.org/r/20170802180609.GA66807@beast Signed-off-by: Kees Cook <keescook@chromium.org> Suggested-by: Daniel Micay <danielmicay@gmail.com> Cc: Rik van Riel <riel@redhat.com> Cc: Tycho Andersen <tycho@docker.com> Cc: Alexander Popov <alex.popov@linux.com> Cc: Christoph Lameter <cl@linux.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
176 lines
5.3 KiB
C
176 lines
5.3 KiB
C
#ifndef _LINUX_SLUB_DEF_H
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#define _LINUX_SLUB_DEF_H
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/*
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* SLUB : A Slab allocator without object queues.
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*
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* (C) 2007 SGI, Christoph Lameter
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*/
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#include <linux/kobject.h>
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enum stat_item {
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ALLOC_FASTPATH, /* Allocation from cpu slab */
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ALLOC_SLOWPATH, /* Allocation by getting a new cpu slab */
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FREE_FASTPATH, /* Free to cpu slab */
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FREE_SLOWPATH, /* Freeing not to cpu slab */
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FREE_FROZEN, /* Freeing to frozen slab */
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FREE_ADD_PARTIAL, /* Freeing moves slab to partial list */
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FREE_REMOVE_PARTIAL, /* Freeing removes last object */
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ALLOC_FROM_PARTIAL, /* Cpu slab acquired from node partial list */
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ALLOC_SLAB, /* Cpu slab acquired from page allocator */
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ALLOC_REFILL, /* Refill cpu slab from slab freelist */
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ALLOC_NODE_MISMATCH, /* Switching cpu slab */
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FREE_SLAB, /* Slab freed to the page allocator */
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CPUSLAB_FLUSH, /* Abandoning of the cpu slab */
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DEACTIVATE_FULL, /* Cpu slab was full when deactivated */
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DEACTIVATE_EMPTY, /* Cpu slab was empty when deactivated */
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DEACTIVATE_TO_HEAD, /* Cpu slab was moved to the head of partials */
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DEACTIVATE_TO_TAIL, /* Cpu slab was moved to the tail of partials */
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DEACTIVATE_REMOTE_FREES,/* Slab contained remotely freed objects */
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DEACTIVATE_BYPASS, /* Implicit deactivation */
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ORDER_FALLBACK, /* Number of times fallback was necessary */
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CMPXCHG_DOUBLE_CPU_FAIL,/* Failure of this_cpu_cmpxchg_double */
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CMPXCHG_DOUBLE_FAIL, /* Number of times that cmpxchg double did not match */
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CPU_PARTIAL_ALLOC, /* Used cpu partial on alloc */
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CPU_PARTIAL_FREE, /* Refill cpu partial on free */
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CPU_PARTIAL_NODE, /* Refill cpu partial from node partial */
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CPU_PARTIAL_DRAIN, /* Drain cpu partial to node partial */
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NR_SLUB_STAT_ITEMS };
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struct kmem_cache_cpu {
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void **freelist; /* Pointer to next available object */
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unsigned long tid; /* Globally unique transaction id */
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struct page *page; /* The slab from which we are allocating */
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#ifdef CONFIG_SLUB_CPU_PARTIAL
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struct page *partial; /* Partially allocated frozen slabs */
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#endif
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#ifdef CONFIG_SLUB_STATS
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unsigned stat[NR_SLUB_STAT_ITEMS];
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#endif
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};
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#ifdef CONFIG_SLUB_CPU_PARTIAL
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#define slub_percpu_partial(c) ((c)->partial)
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#define slub_set_percpu_partial(c, p) \
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({ \
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slub_percpu_partial(c) = (p)->next; \
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})
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#define slub_percpu_partial_read_once(c) READ_ONCE(slub_percpu_partial(c))
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#else
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#define slub_percpu_partial(c) NULL
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#define slub_set_percpu_partial(c, p)
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#define slub_percpu_partial_read_once(c) NULL
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#endif // CONFIG_SLUB_CPU_PARTIAL
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/*
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* Word size structure that can be atomically updated or read and that
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* contains both the order and the number of objects that a slab of the
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* given order would contain.
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*/
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struct kmem_cache_order_objects {
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unsigned long x;
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};
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/*
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* Slab cache management.
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*/
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struct kmem_cache {
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struct kmem_cache_cpu __percpu *cpu_slab;
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/* Used for retriving partial slabs etc */
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unsigned long flags;
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unsigned long min_partial;
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int size; /* The size of an object including meta data */
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int object_size; /* The size of an object without meta data */
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int offset; /* Free pointer offset. */
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#ifdef CONFIG_SLUB_CPU_PARTIAL
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int cpu_partial; /* Number of per cpu partial objects to keep around */
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#endif
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struct kmem_cache_order_objects oo;
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/* Allocation and freeing of slabs */
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struct kmem_cache_order_objects max;
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struct kmem_cache_order_objects min;
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gfp_t allocflags; /* gfp flags to use on each alloc */
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int refcount; /* Refcount for slab cache destroy */
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void (*ctor)(void *);
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int inuse; /* Offset to metadata */
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int align; /* Alignment */
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int reserved; /* Reserved bytes at the end of slabs */
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int red_left_pad; /* Left redzone padding size */
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const char *name; /* Name (only for display!) */
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struct list_head list; /* List of slab caches */
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#ifdef CONFIG_SYSFS
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struct kobject kobj; /* For sysfs */
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struct work_struct kobj_remove_work;
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#endif
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#ifdef CONFIG_MEMCG
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struct memcg_cache_params memcg_params;
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int max_attr_size; /* for propagation, maximum size of a stored attr */
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#ifdef CONFIG_SYSFS
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struct kset *memcg_kset;
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#endif
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#endif
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#ifdef CONFIG_SLAB_FREELIST_HARDENED
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unsigned long random;
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#endif
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#ifdef CONFIG_NUMA
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/*
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* Defragmentation by allocating from a remote node.
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*/
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int remote_node_defrag_ratio;
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#endif
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#ifdef CONFIG_SLAB_FREELIST_RANDOM
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unsigned int *random_seq;
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#endif
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#ifdef CONFIG_KASAN
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struct kasan_cache kasan_info;
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#endif
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struct kmem_cache_node *node[MAX_NUMNODES];
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};
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#ifdef CONFIG_SLUB_CPU_PARTIAL
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#define slub_cpu_partial(s) ((s)->cpu_partial)
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#define slub_set_cpu_partial(s, n) \
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({ \
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slub_cpu_partial(s) = (n); \
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})
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#else
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#define slub_cpu_partial(s) (0)
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#define slub_set_cpu_partial(s, n)
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#endif // CONFIG_SLUB_CPU_PARTIAL
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#ifdef CONFIG_SYSFS
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#define SLAB_SUPPORTS_SYSFS
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void sysfs_slab_release(struct kmem_cache *);
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#else
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static inline void sysfs_slab_release(struct kmem_cache *s)
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{
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}
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#endif
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void object_err(struct kmem_cache *s, struct page *page,
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u8 *object, char *reason);
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void *fixup_red_left(struct kmem_cache *s, void *p);
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static inline void *nearest_obj(struct kmem_cache *cache, struct page *page,
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void *x) {
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void *object = x - (x - page_address(page)) % cache->size;
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void *last_object = page_address(page) +
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(page->objects - 1) * cache->size;
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void *result = (unlikely(object > last_object)) ? last_object : object;
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result = fixup_red_left(cache, result);
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return result;
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}
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#endif /* _LINUX_SLUB_DEF_H */
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