On 2023/6/26 11:18, GONG, Ruiqi wrote: > When exploiting memory vulnerabilities, "heap spraying" is a common > technique targeting those related to dynamic memory allocation (i.e. the > "heap"), and it plays an important role in a successful exploitation. > Basically, it is to overwrite the memory area of vulnerable object by > triggering allocation in other subsystems or modules and therefore > getting a reference to the targeted memory location. It's usable on > various types of vulnerablity including use after free (UAF), heap out- > of-bound write and etc. > > There are (at least) two reasons why the heap can be sprayed: 1) generic > slab caches are shared among different subsystems and modules, and > 2) dedicated slab caches could be merged with the generic ones. > Currently these two factors cannot be prevented at a low cost: the first > one is a widely used memory allocation mechanism, and shutting down slab > merging completely via `slub_nomerge` would be overkill. > > To efficiently prevent heap spraying, we propose the following approach: > to create multiple copies of generic slab caches that will never be > merged, and random one of them will be used at allocation. The random > selection is based on the address of code that calls `kmalloc()`, which > means it is static at runtime (rather than dynamically determined at > each time of allocation, which could be bypassed by repeatedly spraying > in brute force). In other words, the randomness of cache selection will > be with respect to the code address rather than time, i.e. allocations > in different code paths would most likely pick different caches, > although kmalloc() at each place would use the same cache copy whenever > it is executed. In this way, the vulnerable object and memory allocated > in other subsystems and modules will (most probably) be on different > slab caches, which prevents the object from being sprayed. > > Meanwhile, the static random selection is further enhanced with a > per-boot random seed, which prevents the attacker from finding a usable > kmalloc that happens to pick the same cache with the vulnerable > subsystem/module by analyzing the open source code. In other words, with > the per-boot seed, the random selection is static during each time the > system starts and runs, but not across different system startups. > > The overhead of performance has been tested on a 40-core x86 server by > comparing the results of `perf bench all` between the kernels with and > without this patch based on the latest linux-next kernel, which shows > minor difference. A subset of benchmarks are listed below: > > sched/ sched/ syscall/ mem/ mem/ > messaging pipe basic memcpy memset > (sec) (sec) (sec) (GB/sec) (GB/sec) > > control1 0.019 5.459 0.733 15.258789 51.398026 > control2 0.019 5.439 0.730 16.009221 48.828125 > control3 0.019 5.282 0.735 16.009221 48.828125 > control_avg 0.019 5.393 0.733 15.759077 49.684759 > > experiment1 0.019 5.374 0.741 15.500992 46.502976 > experiment2 0.019 5.440 0.746 16.276042 51.398026 > experiment3 0.019 5.242 0.752 15.258789 51.398026 > experiment_avg 0.019 5.352 0.746 15.678608 49.766343 > > The overhead of memory usage was measured by executing `free` after boot > on a QEMU VM with 1GB total memory, and as expected, it's positively > correlated with # of cache copies: > > control 4 copies 8 copies 16 copies > > total 969.8M 968.2M 968.2M 968.2M > used 20.0M 21.9M 24.1M 26.7M > free 936.9M 933.6M 931.4M 928.6M > available 932.2M 928.8M 926.6M 923.9M > > Co-developed-by: Xiu Jianfeng <xiujianfeng@xxxxxxxxxx> > Signed-off-by: Xiu Jianfeng <xiujianfeng@xxxxxxxxxx> > Signed-off-by: GONG, Ruiqi <gongruiqi@xxxxxxxxxxxxxxx> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > --- > > v4: > - Set # of cache copies to 16 and remove config selection. > - Shorten "kmalloc-random-" to "kmalloc-rnd-". > - Update commit log and config's help paragraph. > - Fine-tune PERCPU_DYNAMIC_SIZE_SHIFT to 12 instead of 13 (enough to > pass compilation with allmodconfig and CONFIG_SLUB_TINY=n). > - Some cleanup and typo fixing. > > v3: > - Replace SLAB_RANDOMSLAB with the new existing SLAB_NO_MERGE flag. > - Shorten long code lines by wrapping and renaming. > - Update commit message with latest perf benchmark and additional > theorectical explanation. > - Remove "RFC" from patch title and make it a formal patch > - Link: https://lore.kernel.org/all/20230616111843.3677378-1-gongruiqi@xxxxxxxxxxxxxxx/ > > v2: > - Use hash_64() and a per-boot random seed to select kmalloc() caches. > - Change acceptable # of caches from [4,16] to {2,4,8,16}, which is > more compatible with hashing. > - Supplement results of performance and memory overhead tests. > - Link: https://lore.kernel.org/all/20230508075507.1720950-1-gongruiqi1@xxxxxxxxxx/ > > v1: > - Link: https://lore.kernel.org/all/20230315095459.186113-1-gongruiqi1@xxxxxxxxxx/ > > include/linux/percpu.h | 12 ++++++++--- > include/linux/slab.h | 25 ++++++++++++++++++---- > mm/Kconfig | 16 ++++++++++++++ > mm/kfence/kfence_test.c | 6 ++++-- > mm/slab.c | 2 +- > mm/slab.h | 2 +- > mm/slab_common.c | 47 ++++++++++++++++++++++++++++++++++++----- > 7 files changed, 94 insertions(+), 16 deletions(-) > > diff --git a/include/linux/percpu.h b/include/linux/percpu.h > index 42125cf9c506..7692b5559098 100644 > --- a/include/linux/percpu.h > +++ b/include/linux/percpu.h > @@ -34,6 +34,12 @@ > #define PCPU_BITMAP_BLOCK_BITS (PCPU_BITMAP_BLOCK_SIZE >> \ > PCPU_MIN_ALLOC_SHIFT) > > +#ifdef CONFIG_RANDOM_KMALLOC_CACHES > +#define PERCPU_DYNAMIC_SIZE_SHIFT 12 > +#else > +#define PERCPU_DYNAMIC_SIZE_SHIFT 10 > +#endif > + > /* > * Percpu allocator can serve percpu allocations before slab is > * initialized which allows slab to depend on the percpu allocator. > @@ -41,7 +47,7 @@ > * for this. Keep PERCPU_DYNAMIC_RESERVE equal to or larger than > * PERCPU_DYNAMIC_EARLY_SIZE. > */ > -#define PERCPU_DYNAMIC_EARLY_SIZE (20 << 10) > +#define PERCPU_DYNAMIC_EARLY_SIZE (20 << PERCPU_DYNAMIC_SIZE_SHIFT) > > /* > * PERCPU_DYNAMIC_RESERVE indicates the amount of free area to piggy > @@ -55,9 +61,9 @@ > * intelligent way to determine this would be nice. > */ > #if BITS_PER_LONG > 32 > -#define PERCPU_DYNAMIC_RESERVE (28 << 10) > +#define PERCPU_DYNAMIC_RESERVE (28 << PERCPU_DYNAMIC_SIZE_SHIFT) > #else > -#define PERCPU_DYNAMIC_RESERVE (20 << 10) > +#define PERCPU_DYNAMIC_RESERVE (20 << PERCPU_DYNAMIC_SIZE_SHIFT) > #endif > > extern void *pcpu_base_addr; > diff --git a/include/linux/slab.h b/include/linux/slab.h > index 791f7453a04f..747fc2587b56 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -18,6 +18,7 @@ > #include <linux/types.h> > #include <linux/workqueue.h> > #include <linux/percpu-refcount.h> > +#include <linux/hash.h> > > > /* > @@ -342,6 +343,13 @@ static inline unsigned int arch_slab_minalign(void) > #define SLAB_OBJ_MIN_SIZE (KMALLOC_MIN_SIZE < 16 ? \ > (KMALLOC_MIN_SIZE) : 16) > > +#ifdef CONFIG_RANDOM_KMALLOC_CACHES > +#define RANDOM_KMALLOC_CACHES_NR 16 // # of cache copies > +#define RANDOM_KMALLOC_CACHES_BITS 4 // =log2(_NR), for hashing It's unnecessary to define RANDOM_KMALLOC_CACHES_BITS, use ilog2(RANDOM_KMALLOC_CACHES_NR) directly in kmalloc_type(). > +#else > +#define RANDOM_KMALLOC_CACHES_NR 1 > +#endif > + > /* > * Whenever changing this, take care of that kmalloc_type() and > * create_kmalloc_caches() still work as intended. > @@ -351,7 +359,9 @@ static inline unsigned int arch_slab_minalign(void) > * kmem caches can have both accounted and unaccounted objects. > */ > enum kmalloc_cache_type { > - KMALLOC_NORMAL = 0, > + KMALLOC_RANDOM_START = 0, > + KMALLOC_RANDOM_END = KMALLOC_RANDOM_START + RANDOM_KMALLOC_CACHES_NR - 1, > + KMALLOC_NORMAL = KMALLOC_RANDOM_END, > #ifndef CONFIG_ZONE_DMA > KMALLOC_DMA = KMALLOC_NORMAL, > #endif > @@ -383,14 +393,21 @@ kmalloc_caches[NR_KMALLOC_TYPES][KMALLOC_SHIFT_HIGH + 1]; > (IS_ENABLED(CONFIG_ZONE_DMA) ? __GFP_DMA : 0) | \ > (IS_ENABLED(CONFIG_MEMCG_KMEM) ? __GFP_ACCOUNT : 0)) > > -static __always_inline enum kmalloc_cache_type kmalloc_type(gfp_t flags) > +extern unsigned long random_kmalloc_seed; > + > +static __always_inline enum kmalloc_cache_type kmalloc_type(gfp_t flags, unsigned long caller) > { > /* > * The most common case is KMALLOC_NORMAL, so test for it > * with a single branch for all the relevant flags. > */ > if (likely((flags & KMALLOC_NOT_NORMAL_BITS) == 0)) > +#ifdef CONFIG_RANDOM_KMALLOC_CACHES > + return KMALLOC_RANDOM_START + hash_64(caller ^ random_kmalloc_seed, > + RANDOM_KMALLOC_CACHES_BITS); > +#else > return KMALLOC_NORMAL; > +#endif > > /* > * At least one of the flags has to be set. Their priorities in > @@ -577,7 +594,7 @@ static __always_inline __alloc_size(1) void *kmalloc(size_t size, gfp_t flags) > > index = kmalloc_index(size); > return kmalloc_trace( > - kmalloc_caches[kmalloc_type(flags)][index], > + kmalloc_caches[kmalloc_type(flags, _RET_IP_)][index], > flags, size); > } > return __kmalloc(size, flags); > @@ -593,7 +610,7 @@ static __always_inline __alloc_size(1) void *kmalloc_node(size_t size, gfp_t fla > > index = kmalloc_index(size); > return kmalloc_node_trace( > - kmalloc_caches[kmalloc_type(flags)][index], > + kmalloc_caches[kmalloc_type(flags, _RET_IP_)][index], > flags, node, size); > } > return __kmalloc_node(size, flags, node); > diff --git a/mm/Kconfig b/mm/Kconfig > index a3c95338cd3a..e9dc606c9317 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -337,6 +337,22 @@ config SLUB_CPU_PARTIAL > which requires the taking of locks that may cause latency spikes. > Typically one would choose no for a realtime system. > > +config RANDOM_KMALLOC_CACHES > + default n > + depends on SLUB > + bool "Random slab caches for normal kmalloc" > + help > + A hardening feature that creates multiple copies of slab caches for > + normal kmalloc allocation and makes kmalloc randomly pick one based > + on code address, which makes the attackers unable to spray vulnerable > + memory objects on the heap for the purpose of exploiting memory > + vulnerabilities. > + > + Currently the number of copies is set to 16, a reasonably large value > + that effectively diverges the memory objects allocated for different > + subsystems or modules into different caches, at the expense of about > + 7 MB of memory overhead. > + > endmenu # SLAB allocator options > > config SHUFFLE_PAGE_ALLOCATOR > diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c > index 9e008a336d9f..7f5ffb490328 100644 > --- a/mm/kfence/kfence_test.c > +++ b/mm/kfence/kfence_test.c > @@ -212,7 +212,8 @@ static void test_cache_destroy(void) > > static inline size_t kmalloc_cache_alignment(size_t size) > { > - return kmalloc_caches[kmalloc_type(GFP_KERNEL)][__kmalloc_index(size, false)]->align; > + enum kmalloc_cache_type type = kmalloc_type(GFP_KERNEL, _RET_IP_); > + return kmalloc_caches[type][__kmalloc_index(size, false)]->align; > } > > /* Must always inline to match stack trace against caller. */ > @@ -282,8 +283,9 @@ static void *test_alloc(struct kunit *test, size_t size, gfp_t gfp, enum allocat > > if (is_kfence_address(alloc)) { > struct slab *slab = virt_to_slab(alloc); > + enum kmalloc_cache_type type = kmalloc_type(GFP_KERNEL, _RET_IP_); > struct kmem_cache *s = test_cache ?: > - kmalloc_caches[kmalloc_type(GFP_KERNEL)][__kmalloc_index(size, false)]; > + kmalloc_caches[type][__kmalloc_index(size, false)]; > > /* > * Verify that various helpers return the right values > diff --git a/mm/slab.c b/mm/slab.c > index 88194391d553..9ad3d0f2d1a5 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -1670,7 +1670,7 @@ static size_t calculate_slab_order(struct kmem_cache *cachep, > if (freelist_size > KMALLOC_MAX_CACHE_SIZE) { > freelist_cache_size = PAGE_SIZE << get_order(freelist_size); > } else { > - freelist_cache = kmalloc_slab(freelist_size, 0u); > + freelist_cache = kmalloc_slab(freelist_size, 0u, _RET_IP_); > if (!freelist_cache) > continue; > freelist_cache_size = freelist_cache->size; > diff --git a/mm/slab.h b/mm/slab.h > index 6a5633b25eb5..4ebe3bdfc17c 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -282,7 +282,7 @@ void setup_kmalloc_cache_index_table(void); > void create_kmalloc_caches(slab_flags_t); > > /* Find the kmalloc slab corresponding for a certain size */ > -struct kmem_cache *kmalloc_slab(size_t, gfp_t); > +struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags, unsigned long caller); > > void *__kmem_cache_alloc_node(struct kmem_cache *s, gfp_t gfpflags, > int node, size_t orig_size, > diff --git a/mm/slab_common.c b/mm/slab_common.c > index fe436d35f333..6f385956ef07 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -678,6 +678,11 @@ kmalloc_caches[NR_KMALLOC_TYPES][KMALLOC_SHIFT_HIGH + 1] __ro_after_init = > { /* initialization for https://bugs.llvm.org/show_bug.cgi?id=42570 */ }; > EXPORT_SYMBOL(kmalloc_caches); > > +#ifdef CONFIG_RANDOM_KMALLOC_CACHES > +unsigned long random_kmalloc_seed __ro_after_init; > +EXPORT_SYMBOL(random_kmalloc_seed); > +#endif > + > /* > * Conversion table for small slabs sizes / 8 to the index in the > * kmalloc array. This is necessary for slabs < 192 since we have non power > @@ -720,7 +725,7 @@ static inline unsigned int size_index_elem(unsigned int bytes) > * Find the kmem_cache structure that serves a given size of > * allocation > */ > -struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags) > +struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags, unsigned long caller) > { > unsigned int index; > > @@ -735,7 +740,7 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags) > index = fls(size - 1); > } > > - return kmalloc_caches[kmalloc_type(flags)][index]; > + return kmalloc_caches[kmalloc_type(flags, caller)][index]; > } > > size_t kmalloc_size_roundup(size_t size) > @@ -753,7 +758,7 @@ size_t kmalloc_size_roundup(size_t size) > return PAGE_SIZE << get_order(size); > > /* The flags don't matter since size_index is common to all. */ > - c = kmalloc_slab(size, GFP_KERNEL); > + c = kmalloc_slab(size, GFP_KERNEL, _RET_IP_); > return c ? c->object_size : 0; > } > EXPORT_SYMBOL(kmalloc_size_roundup); > @@ -776,12 +781,36 @@ EXPORT_SYMBOL(kmalloc_size_roundup); > #define KMALLOC_RCL_NAME(sz) > #endif > > +#ifdef CONFIG_RANDOM_KMALLOC_CACHES > +#define __KMALLOC_RANDOM_CONCAT(a, b) a ## b > +#define KMALLOC_RANDOM_NAME(N, sz) __KMALLOC_RANDOM_CONCAT(KMA_RAND_, N)(sz) > +#define KMA_RAND_1(sz) .name[KMALLOC_RANDOM_START + 0] = "kmalloc-rnd-01-" #sz, > +#define KMA_RAND_2(sz) KMA_RAND_1(sz) .name[KMALLOC_RANDOM_START + 1] = "kmalloc-rnd-02-" #sz, > +#define KMA_RAND_3(sz) KMA_RAND_2(sz) .name[KMALLOC_RANDOM_START + 2] = "kmalloc-rnd-03-" #sz, > +#define KMA_RAND_4(sz) KMA_RAND_3(sz) .name[KMALLOC_RANDOM_START + 3] = "kmalloc-rnd-04-" #sz, > +#define KMA_RAND_5(sz) KMA_RAND_4(sz) .name[KMALLOC_RANDOM_START + 4] = "kmalloc-rnd-05-" #sz, > +#define KMA_RAND_6(sz) KMA_RAND_5(sz) .name[KMALLOC_RANDOM_START + 5] = "kmalloc-rnd-06-" #sz, > +#define KMA_RAND_7(sz) KMA_RAND_6(sz) .name[KMALLOC_RANDOM_START + 6] = "kmalloc-rnd-07-" #sz, > +#define KMA_RAND_8(sz) KMA_RAND_7(sz) .name[KMALLOC_RANDOM_START + 7] = "kmalloc-rnd-08-" #sz, > +#define KMA_RAND_9(sz) KMA_RAND_8(sz) .name[KMALLOC_RANDOM_START + 8] = "kmalloc-rnd-09-" #sz, > +#define KMA_RAND_10(sz) KMA_RAND_9(sz) .name[KMALLOC_RANDOM_START + 9] = "kmalloc-rnd-10-" #sz, > +#define KMA_RAND_11(sz) KMA_RAND_10(sz) .name[KMALLOC_RANDOM_START + 10] = "kmalloc-rnd-11-" #sz, > +#define KMA_RAND_12(sz) KMA_RAND_11(sz) .name[KMALLOC_RANDOM_START + 11] = "kmalloc-rnd-12-" #sz, > +#define KMA_RAND_13(sz) KMA_RAND_12(sz) .name[KMALLOC_RANDOM_START + 12] = "kmalloc-rnd-13-" #sz, > +#define KMA_RAND_14(sz) KMA_RAND_13(sz) .name[KMALLOC_RANDOM_START + 13] = "kmalloc-rnd-14-" #sz, > +#define KMA_RAND_15(sz) KMA_RAND_14(sz) .name[KMALLOC_RANDOM_START + 14] = "kmalloc-rnd-15-" #sz, > +#define KMA_RAND_16(sz) KMA_RAND_15(sz) .name[KMALLOC_RANDOM_START + 15] = "kmalloc-rnd-16-" #sz, > +#else // CONFIG_RANDOM_KMALLOC_CACHES > +#define KMALLOC_RANDOM_NAME(N, sz) > +#endif > + > #define INIT_KMALLOC_INFO(__size, __short_size) \ > { \ > .name[KMALLOC_NORMAL] = "kmalloc-" #__short_size, \ > KMALLOC_RCL_NAME(__short_size) \ > KMALLOC_CGROUP_NAME(__short_size) \ > KMALLOC_DMA_NAME(__short_size) \ > + KMALLOC_RANDOM_NAME(RANDOM_KMALLOC_CACHES_NR, __short_size) \ > .size = __size, \ > } > > @@ -890,6 +919,11 @@ new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags) > flags |= SLAB_CACHE_DMA; > } > > +#ifdef CONFIG_RANDOM_KMALLOC_CACHES > + if (type >= KMALLOC_RANDOM_START && type <= KMALLOC_RANDOM_END) > + flags |= SLAB_NO_MERGE; > +#endif > + > if (minalign > ARCH_KMALLOC_MINALIGN) { > aligned_size = ALIGN(aligned_size, minalign); > aligned_idx = __kmalloc_index(aligned_size, false); > @@ -923,7 +957,7 @@ void __init create_kmalloc_caches(slab_flags_t flags) > /* > * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined > */ > - for (type = KMALLOC_NORMAL; type < NR_KMALLOC_TYPES; type++) { > + for (type = KMALLOC_RANDOM_START; type < NR_KMALLOC_TYPES; type++) { > for (i = KMALLOC_SHIFT_LOW; i <= KMALLOC_SHIFT_HIGH; i++) { > if (!kmalloc_caches[type][i]) > new_kmalloc_cache(i, type, flags); > @@ -941,6 +975,9 @@ void __init create_kmalloc_caches(slab_flags_t flags) > new_kmalloc_cache(2, type, flags); > } > } > +#ifdef CONFIG_RANDOM_KMALLOC_CACHES > + random_kmalloc_seed = get_random_u64(); > +#endif > > /* Kmalloc array is now usable */ > slab_state = UP; > @@ -976,7 +1013,7 @@ void *__do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller > return ret; > } > > - s = kmalloc_slab(size, flags); > + s = kmalloc_slab(size, flags, caller); > > if (unlikely(ZERO_OR_NULL_PTR(s))) > return s;
