diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index facc20a..db7ec30 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2808,6 +2808,10 @@ the specified number of seconds. This is to be used if your oopses keep scrolling off the screen. + pax_sanitize_slab= + 0/1 to disable/enable slab object sanitization (disabled by + default). + pcbit= [HW,ISDN] pcd. [PARIDE] diff --git a/fs/buffer.c b/fs/buffer.c index 9196f2a..6215406 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -3512,7 +3512,7 @@ void __init buffer_init(void) bh_cachep = kmem_cache_create("buffer_head", sizeof(struct buffer_head), 0, (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC| - SLAB_MEM_SPREAD), + SLAB_MEM_SPREAD|SLAB_NO_SANITIZE), NULL); /* diff --git a/fs/dcache.c b/fs/dcache.c index b1ff5be..e869514 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -3619,7 +3619,8 @@ void __init vfs_caches_init_early(void) void __init vfs_caches_init(void) { names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0, - SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); + SLAB_HWCACHE_ALIGN|SLAB_PANIC| + SLAB_NO_SANITIZE, NULL); dcache_init(); inode_init(); diff --git a/include/linux/slab.h b/include/linux/slab.h index 3c37a8c..341210a 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -23,6 +23,13 @@ #define SLAB_CONSISTENCY_CHECKS 0x00000100UL /* DEBUG: Perform (expensive) checks on alloc/free */ #define SLAB_RED_ZONE 0x00000400UL /* DEBUG: Red zone objs in a cache */ #define SLAB_POISON 0x00000800UL /* DEBUG: Poison objects */ + +#ifdef CONFIG_PAX_MEMORY_SANITIZE +#define SLAB_NO_SANITIZE 0x00001000UL /* PaX: Do not sanitize objs on free */ +#else +#define SLAB_NO_SANITIZE 0x00000000UL +#endif + #define SLAB_HWCACHE_ALIGN 0x00002000UL /* Align objs on cache lines */ #define SLAB_CACHE_DMA 0x00004000UL /* Use GFP_DMA memory */ #define SLAB_STORE_USER 0x00010000UL /* DEBUG: Store the last owner for bug hunting */ diff --git a/kernel/fork.c b/kernel/fork.c index 631a65c..d4cd8d4 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2173,7 +2173,7 @@ void __init proc_caches_init(void) sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK|SLAB_ACCOUNT, NULL); - vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_ACCOUNT); + vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_ACCOUNT|SLAB_NO_SANITIZE); mmap_init(); nsproxy_cache_init(); } diff --git a/mm/rmap.c b/mm/rmap.c index f683801..d863239 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -430,10 +430,10 @@ static void anon_vma_ctor(void *data) void __init anon_vma_init(void) { anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma), - 0, SLAB_DESTROY_BY_RCU|SLAB_PANIC|SLAB_ACCOUNT, + 0, SLAB_DESTROY_BY_RCU|SLAB_PANIC|SLAB_ACCOUNT|SLAB_NO_SANITIZE, anon_vma_ctor); anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, - SLAB_PANIC|SLAB_ACCOUNT); + SLAB_PANIC|SLAB_ACCOUNT|SLAB_NO_SANITIZE); } /* diff --git a/mm/slab.c b/mm/slab.c index 807d86c..6cac198 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3520,6 +3520,17 @@ void ___cache_free(struct kmem_cache *cachep, void *objp, struct array_cache *ac = cpu_cache_get(cachep); check_irq_off(); + +#ifdef CONFIG_PAX_MEMORY_SANITIZE + if (pax_sanitize_slab) { + if (!(cachep->flags & (SLAB_POISON | SLAB_NO_SANITIZE))) { + memset(objp, PAX_MEMORY_SANITIZE_VALUE, cachep->object_size); + if (cachep->ctor) + cachep->ctor(objp); + } + } +#endif + kmemleak_free_recursive(objp, cachep->flags); objp = cache_free_debugcheck(cachep, objp, caller); diff --git a/mm/slab.h b/mm/slab.h index 65e7c3f..fc7e00e 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -77,6 +77,15 @@ extern const struct kmalloc_info_struct { unsigned long size; } kmalloc_info[]; +#ifdef CONFIG_PAX_MEMORY_SANITIZE +#ifdef CONFIG_X86_64 +#define PAX_MEMORY_SANITIZE_VALUE '\xfe' +#else +#define PAX_MEMORY_SANITIZE_VALUE '\xff' +#endif +extern bool pax_sanitize_slab; +#endif + unsigned long calculate_alignment(unsigned long flags, unsigned long align, unsigned long size); diff --git a/mm/slab_common.c b/mm/slab_common.c index 09d0e84..d87c631 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -49,7 +49,11 @@ static DECLARE_WORK(slab_caches_to_rcu_destroy_work, * Merge control. If this is set then no merging of slab caches will occur. * (Could be removed. This was introduced to pacify the merge skeptics.) */ +#ifdef CONFIG_PAX_MEMORY_SANITIZE +static int slab_nomerge = 1; +#else static int slab_nomerge; +#endif static int __init setup_slab_nomerge(char *str) { @@ -72,6 +76,20 @@ unsigned int kmem_cache_size(struct kmem_cache *s) } EXPORT_SYMBOL(kmem_cache_size); +#ifdef CONFIG_PAX_MEMORY_SANITIZE +bool pax_sanitize_slab = false; +static int __init pax_sanitize_slab_setup(char *str) +{ + if (!str) + return -EINVAL; + + pax_sanitize_slab = !!simple_strtol(str, NULL, 0); + pr_info("%sabled PaX slab sanitization\n", pax_sanitize_slab ? "En" : "Dis"); + return 0; +} +early_param("pax_sanitize_slab", pax_sanitize_slab_setup); +#endif + #ifdef CONFIG_DEBUG_VM static int kmem_cache_sanity_check(const char *name, size_t size) { @@ -264,7 +282,11 @@ static inline void memcg_unlink_cache(struct kmem_cache *s) */ int slab_unmergeable(struct kmem_cache *s) { - if (slab_nomerge || (s->flags & SLAB_NEVER_MERGE)) + if (slab_nomerge || (s->flags & SLAB_NEVER_MERGE) +#ifdef CONFIG_PAX_MEMORY_SANITIZE + || pax_sanitize_slab +#endif + ) return 1; if (!is_root_cache(s)) @@ -287,7 +309,11 @@ struct kmem_cache *find_mergeable(size_t size, size_t align, { struct kmem_cache *s; - if (slab_nomerge) + if (slab_nomerge +#ifdef CONFIG_PAX_MEMORY_SANITIZE + || pax_sanitize_slab +#endif + ) return NULL; if (ctor) @@ -453,6 +479,11 @@ kmem_cache_create(const char *name, size_t size, size_t align, * passed flags. */ flags &= CACHE_CREATE_MASK; + +#ifdef CONFIG_PAX_MEMORY_SANITIZE + if (flags & SLAB_DESTROY_BY_RCU) + flags |= SLAB_NO_SANITIZE; +#endif s = __kmem_cache_alias(name, size, align, flags, ctor); if (s) diff --git a/mm/slob.c b/mm/slob.c index eac04d43..f455845 100644 --- a/mm/slob.c +++ b/mm/slob.c @@ -365,6 +365,11 @@ static void slob_free(void *block, int size) return; } +#ifdef CONFIG_PAX_MEMORY_SANITIZE + if (pax_sanitize_slab && !(c && (c->flags & SLAB_NO_SANITIZE))) + memset(block, PAX_MEMORY_SANITIZE_VALUE, size); +#endif + if (!slob_page_free(sp)) { /* This slob page is about to become partially free. Easy! */ sp->units = units; diff --git a/mm/slub.c b/mm/slub.c index 7f4bc70..a913874 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2959,6 +2959,23 @@ static __always_inline void slab_free(struct kmem_cache *s, struct page *page, unsigned long addr) { slab_free_freelist_hook(s, head, tail); + +#ifdef CONFIG_PAX_MEMORY_SANITIZE + if (pax_sanitize_slab && !(s->flags & SLAB_NO_SANITIZE)) { + int offset = s->offset ? 0 : sizeof(void *); + void *x = head; + + while (1) { + memset(x + offset, PAX_MEMORY_SANITIZE_VALUE, s->object_size - offset); + if (s->ctor) + s->ctor(x); + if (x == tail_obj) + break; + x = get_freepointer(s, x); + } + } +#endif + /* * slab_free_freelist_hook() could have put the items into quarantine. * If so, no need to free them. @@ -3456,6 +3473,9 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order) s->inuse = size; if (((flags & (SLAB_DESTROY_BY_RCU | SLAB_POISON)) || +#ifdef CONFIG_PAX_MEMORY_SANITIZE + (pax_sanitize_slab && !(flags & SLAB_NO_SANITIZE)) || +#endif s->ctor)) { /* * Relocate free pointer after the object if it is not diff --git a/net/core/skbuff.c b/net/core/skbuff.c index f1d0459..dc2922f3 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -3474,12 +3474,14 @@ void __init skb_init(void) skbuff_head_cache = kmem_cache_create("skbuff_head_cache", sizeof(struct sk_buff), 0, - SLAB_HWCACHE_ALIGN|SLAB_PANIC, + SLAB_HWCACHE_ALIGN|SLAB_PANIC| + SLAB_NO_SANITIZE, NULL); skbuff_fclone_cache = kmem_cache_create("skbuff_fclone_cache", sizeof(struct sk_buff_fclones), 0, - SLAB_HWCACHE_ALIGN|SLAB_PANIC, + SLAB_HWCACHE_ALIGN|SLAB_PANIC| + SLAB_NO_SANITIZE, NULL); } diff --git a/security/Kconfig b/security/Kconfig index d900f47..fba9613 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -6,6 +6,37 @@ menu "Security options" source security/keys/Kconfig +menu "Miscellaneous hardening features" + +config PAX_MEMORY_SANITIZE + bool "Sanitize the freed memory" + default y + help + By saying Y here the kernel will erase the contents of slab objects + as soon as they are freed. This in turn reduces the lifetime of data + stored in them, making it less likely that sensitive information such + as passwords, cryptographic secrets, etc stay in memory for too long. + + This is especially useful for programs whose runtime is short, long + lived processes and the kernel itself benefit from this as long as + they ensure timely freeing of memory that may hold sensitive + information. + + A nice side effect of the sanitization of slab objects is the + reduction of possible info leaks caused by padding bytes within the + leaky structures. Use-after-free bugs for structures containing + pointers can also be detected as dereferencing the sanitized pointer + will generate an access violation. + + The tradeoff is performance impact, on a single CPU system kernel + compilation sees a 3% slowdown, other systems and workloads may vary + and you are advised to test this feature on your expected workload + before deploying it. + + Slab sanitization can be disabled with the kernel commandline + parameter "pax_sanitize_slab=0". +endmenu + config SECURITY_DMESG_RESTRICT bool "Restrict unprivileged access to the kernel syslog" default n