| Message ID | d3f5102da9792370158ed02203d8066dd5e07ff7.1537383101.git.andreyknvl@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kasan: add software tag-based mode for arm64 | expand |
On Wed, Sep 19, 2018 at 8:54 PM, Andrey Konovalov <andreyknvl@google.com> wrote: > This commit adds tag-based KASAN specific hooks implementation and > adjusts common generic and tag-based KASAN ones. > > 1. When a new slab cache is created, tag-based KASAN rounds up the size of > the objects in this cache to KASAN_SHADOW_SCALE_SIZE (== 16). > > 2. On each kmalloc tag-based KASAN generates a random tag, sets the shadow > memory, that corresponds to this object to this tag, and embeds this > tag value into the top byte of the returned pointer. > > 3. On each kfree tag-based KASAN poisons the shadow memory with a random > tag to allow detection of use-after-free bugs. > > The rest of the logic of the hook implementation is very much similar to > the one provided by generic KASAN. Tag-based KASAN saves allocation and > free stack metadata to the slab object the same way generic KASAN does. > > Signed-off-by: Andrey Konovalov <andreyknvl@google.com> > --- > mm/kasan/common.c | 118 ++++++++++++++++++++++++++++++++++++++-------- > mm/kasan/kasan.h | 8 ++++ > mm/kasan/tags.c | 48 +++++++++++++++++++ > 3 files changed, 155 insertions(+), 19 deletions(-) > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index 7134e75447ff..d368095feb6c 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -140,6 +140,13 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value) > { > void *shadow_start, *shadow_end; > > + /* > + * Perform shadow offset calculation based on untagged address, as > + * some of the callers (e.g. kasan_poison_object_data) pass tagged > + * addresses to this function. > + */ > + address = reset_tag(address); > + > shadow_start = kasan_mem_to_shadow(address); > shadow_end = kasan_mem_to_shadow(address + size); > > @@ -148,11 +155,24 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value) > > void kasan_unpoison_shadow(const void *address, size_t size) > { > - kasan_poison_shadow(address, size, 0); > + u8 tag = get_tag(address); > + > + /* > + * Perform shadow offset calculation based on untagged address, as > + * some of the callers (e.g. kasan_unpoison_object_data) pass tagged > + * addresses to this function. > + */ > + address = reset_tag(address); > + > + kasan_poison_shadow(address, size, tag); > > if (size & KASAN_SHADOW_MASK) { > u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size); > - *shadow = size & KASAN_SHADOW_MASK; > + > + if (IS_ENABLED(CONFIG_KASAN_SW_TAGS)) > + *shadow = tag; > + else > + *shadow = size & KASAN_SHADOW_MASK; > } > } > > @@ -200,8 +220,9 @@ void kasan_unpoison_stack_above_sp_to(const void *watermark) > > void kasan_alloc_pages(struct page *page, unsigned int order) > { > - if (likely(!PageHighMem(page))) > - kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order); > + if (unlikely(PageHighMem(page))) > + return; > + kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order); > } > > void kasan_free_pages(struct page *page, unsigned int order) > @@ -218,6 +239,9 @@ void kasan_free_pages(struct page *page, unsigned int order) > */ > static inline unsigned int optimal_redzone(unsigned int object_size) > { > + if (IS_ENABLED(CONFIG_KASAN_SW_TAGS)) > + return 0; > + > return > object_size <= 64 - 16 ? 16 : > object_size <= 128 - 32 ? 32 : > @@ -232,6 +256,7 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size, > slab_flags_t *flags) > { > unsigned int orig_size = *size; > + unsigned int redzone_size; > int redzone_adjust; > > /* Add alloc meta. */ > @@ -239,20 +264,20 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size, > *size += sizeof(struct kasan_alloc_meta); > > /* Add free meta. */ > - if (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor || > - cache->object_size < sizeof(struct kasan_free_meta)) { > + if (IS_ENABLED(CONFIG_KASAN_GENERIC) && > + (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor || > + cache->object_size < sizeof(struct kasan_free_meta))) { > cache->kasan_info.free_meta_offset = *size; > *size += sizeof(struct kasan_free_meta); > } > - redzone_adjust = optimal_redzone(cache->object_size) - > - (*size - cache->object_size); > > + redzone_size = optimal_redzone(cache->object_size); > + redzone_adjust = redzone_size - (*size - cache->object_size); > if (redzone_adjust > 0) > *size += redzone_adjust; > > *size = min_t(unsigned int, KMALLOC_MAX_SIZE, > - max(*size, cache->object_size + > - optimal_redzone(cache->object_size))); > + max(*size, cache->object_size + redzone_size)); > > /* > * If the metadata doesn't fit, don't enable KASAN at all. > @@ -265,6 +290,8 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size, > return; > } > > + cache->align = round_up(cache->align, KASAN_SHADOW_SCALE_SIZE); > + > *flags |= SLAB_KASAN; > } > > @@ -319,6 +346,28 @@ void *kasan_init_slab_obj(struct kmem_cache *cache, const void *object) > alloc_info = get_alloc_info(cache, object); > __memset(alloc_info, 0, sizeof(*alloc_info)); > > + /* > + * Since it's desirable to only call object contructors ones during s/ones/once/ > + * slab allocation, we preassign tags to all such objects. While we are here, it can make sense to mention that we can't repaint objects with ctors after reallocation (even for non-SLAB_TYPESAFE_BY_RCU) because the ctor code can memorize pointer to the object somewhere (e.g. in the object itself). Then if we repaint it, the old memorized pointer will become invalid. > + * Also preassign tags for SLAB_TYPESAFE_BY_RCU slabs to avoid > + * use-after-free reports. > + * For SLAB allocator we can't preassign tags randomly since the > + * freelist is stored as an array of indexes instead of a linked > + * list. Assign tags based on objects indexes, so that objects that > + * are next to each other get different tags. > + */ > + if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) && > + (cache->ctor || cache->flags & SLAB_TYPESAFE_BY_RCU)) { > +#ifdef CONFIG_SLAB > + struct page *page = virt_to_page(object); > + u8 tag = (u8)obj_to_index(cache, page, (void *)object); > +#else > + u8 tag = random_tag(); > +#endif This looks much better now as compared to the 2 additional callbacks in the previous version. > + > + object = set_tag(object, tag); > + } > + > return (void *)object; > } > > @@ -327,15 +376,30 @@ void *kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags) > return kasan_kmalloc(cache, object, cache->object_size, flags); > } > > +static inline bool shadow_invalid(u8 tag, s8 shadow_byte) > +{ > + if (IS_ENABLED(CONFIG_KASAN_GENERIC)) > + return shadow_byte < 0 || > + shadow_byte >= KASAN_SHADOW_SCALE_SIZE; > + else > + return tag != (u8)shadow_byte; > +} > + > static bool __kasan_slab_free(struct kmem_cache *cache, void *object, > unsigned long ip, bool quarantine) > { > s8 shadow_byte; > + u8 tag; > + void *tagged_object; > unsigned long rounded_up_size; > > + tag = get_tag(object); > + tagged_object = object; > + object = reset_tag(object); > + > if (unlikely(nearest_obj(cache, virt_to_head_page(object), object) != > object)) { > - kasan_report_invalid_free(object, ip); > + kasan_report_invalid_free(tagged_object, ip); > return true; > } > > @@ -344,20 +408,22 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object, > return false; > > shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object)); > - if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) { > - kasan_report_invalid_free(object, ip); > + if (shadow_invalid(tag, shadow_byte)) { > + kasan_report_invalid_free(tagged_object, ip); > return true; > } > > rounded_up_size = round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE); > kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE); > > - if (!quarantine || unlikely(!(cache->flags & SLAB_KASAN))) > + if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) || > + unlikely(!(cache->flags & SLAB_KASAN))) > return false; > > set_track(&get_alloc_info(cache, object)->free_track, GFP_NOWAIT); > quarantine_put(get_free_info(cache, object), cache); > - return true; > + > + return IS_ENABLED(CONFIG_KASAN_GENERIC); > } > > bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip) > @@ -370,6 +436,7 @@ void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size, > { > unsigned long redzone_start; > unsigned long redzone_end; > + u8 tag; > > if (gfpflags_allow_blocking(flags)) > quarantine_reduce(); > @@ -382,14 +449,27 @@ void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size, > redzone_end = round_up((unsigned long)object + cache->object_size, > KASAN_SHADOW_SCALE_SIZE); > > - kasan_unpoison_shadow(object, size); > + /* See the comment in kasan_init_slab_obj regarding preassigned tags */ > + if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) && > + (cache->ctor || cache->flags & SLAB_TYPESAFE_BY_RCU)) { > +#ifdef CONFIG_SLAB > + struct page *page = virt_to_page(object); > + > + tag = (u8)obj_to_index(cache, page, (void *)object); > +#else > + tag = get_tag(object); > +#endif This kinda _almost_ matches the chunk of code in kasan_init_slab_obj, but not exactly. Wonder if there is some nice way to unify this code? Maybe something like: static u8 tag_for_object(struct kmem_cache *cache, const void *object, new bool) { if (!IS_ENABLED(CONFIG_KASAN_SW_TAGS) || !cache->ctor && !(cache->flags & SLAB_TYPESAFE_BY_RCU)) return random_tag(); #ifdef CONFIG_SLAB struct page *page = virt_to_page(object); return (u8)obj_to_index(cache, page, (void *)object); #else return new ? random_tag() : get_tag(object); #endif } Then we can call this in both places. As a side effect this will assign tags to pointers during slab initialization even if we don't have ctors, but it should be fine (?). > + } else > + tag = random_tag(); > + > + kasan_unpoison_shadow(set_tag(object, tag), size); > kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start, > KASAN_KMALLOC_REDZONE); > > if (cache->flags & SLAB_KASAN) > set_track(&get_alloc_info(cache, object)->alloc_track, flags); > > - return (void *)object; > + return set_tag(object, tag); > } > EXPORT_SYMBOL(kasan_kmalloc); > > @@ -439,7 +519,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip) > page = virt_to_head_page(ptr); > > if (unlikely(!PageSlab(page))) { > - if (ptr != page_address(page)) { > + if (reset_tag(ptr) != page_address(page)) { > kasan_report_invalid_free(ptr, ip); > return; > } > @@ -452,7 +532,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip) > > void kasan_kfree_large(void *ptr, unsigned long ip) > { > - if (ptr != page_address(virt_to_head_page(ptr))) > + if (reset_tag(ptr) != page_address(virt_to_head_page(ptr))) > kasan_report_invalid_free(ptr, ip); > /* The object will be poisoned by page_alloc. */ > } > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h > index a2533b890248..a3db6b8efe7a 100644 > --- a/mm/kasan/kasan.h > +++ b/mm/kasan/kasan.h > @@ -12,10 +12,18 @@ > #define KASAN_TAG_INVALID 0xFE /* inaccessible memory tag */ > #define KASAN_TAG_MAX 0xFD /* maximum value for random tags */ > > +#ifdef CONFIG_KASAN_GENERIC > #define KASAN_FREE_PAGE 0xFF /* page was freed */ > #define KASAN_PAGE_REDZONE 0xFE /* redzone for kmalloc_large allocations */ > #define KASAN_KMALLOC_REDZONE 0xFC /* redzone inside slub object */ > #define KASAN_KMALLOC_FREE 0xFB /* object was freed (kmem_cache_free/kfree) */ > +#else > +#define KASAN_FREE_PAGE KASAN_TAG_INVALID > +#define KASAN_PAGE_REDZONE KASAN_TAG_INVALID > +#define KASAN_KMALLOC_REDZONE KASAN_TAG_INVALID > +#define KASAN_KMALLOC_FREE KASAN_TAG_INVALID > +#endif > + > #define KASAN_GLOBAL_REDZONE 0xFA /* redzone for global variable */ > > /* > diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c > index 700323946867..a3cca11e4fed 100644 > --- a/mm/kasan/tags.c > +++ b/mm/kasan/tags.c > @@ -78,15 +78,60 @@ void *kasan_reset_tag(const void *addr) > void check_memory_region(unsigned long addr, size_t size, bool write, > unsigned long ret_ip) > { > + u8 tag; > + u8 *shadow_first, *shadow_last, *shadow; > + void *untagged_addr; > + > + if (unlikely(size == 0)) > + return; > + > + tag = get_tag((const void *)addr); > + > + /* > + * Ignore accesses for pointers tagged with 0xff (native kernel > + * pointer tag) to suppress false positives caused by kmap. > + * > + * Some kernel code was written to account for archs that don't keep > + * high memory mapped all the time, but rather map and unmap particular > + * pages when needed. Instead of storing a pointer to the kernel memory, > + * this code saves the address of the page structure and offset within > + * that page for later use. Those pages are then mapped and unmapped > + * with kmap/kunmap when necessary and virt_to_page is used to get the > + * virtual address of the page. For arm64 (that keeps the high memory > + * mapped all the time), kmap is turned into a page_address call. > + > + * The issue is that with use of the page_address + virt_to_page > + * sequence the top byte value of the original pointer gets lost (gets > + * set to KASAN_TAG_KERNEL (0xFF)). > + */ > + if (tag == KASAN_TAG_KERNEL) > + return; > + > + untagged_addr = reset_tag((const void *)addr); > + if (unlikely(untagged_addr < > + kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) { > + kasan_report(addr, size, write, ret_ip); > + return; > + } > + shadow_first = kasan_mem_to_shadow(untagged_addr); > + shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1); > + for (shadow = shadow_first; shadow <= shadow_last; shadow++) { > + if (*shadow != tag) { > + kasan_report(addr, size, write, ret_ip); > + return; > + } > + } > } > > #define DEFINE_HWASAN_LOAD_STORE(size) \ > void __hwasan_load##size##_noabort(unsigned long addr) \ > { \ > + check_memory_region(addr, size, false, _RET_IP_); \ > } \ > EXPORT_SYMBOL(__hwasan_load##size##_noabort); \ > void __hwasan_store##size##_noabort(unsigned long addr) \ > { \ > + check_memory_region(addr, size, true, _RET_IP_); \ > } \ > EXPORT_SYMBOL(__hwasan_store##size##_noabort) > > @@ -98,15 +143,18 @@ DEFINE_HWASAN_LOAD_STORE(16); > > void __hwasan_loadN_noabort(unsigned long addr, unsigned long size) > { > + check_memory_region(addr, size, false, _RET_IP_); > } > EXPORT_SYMBOL(__hwasan_loadN_noabort); > > void __hwasan_storeN_noabort(unsigned long addr, unsigned long size) > { > + check_memory_region(addr, size, true, _RET_IP_); > } > EXPORT_SYMBOL(__hwasan_storeN_noabort); > > void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size) > { > + kasan_poison_shadow((void *)addr, size, tag); > } > EXPORT_SYMBOL(__hwasan_tag_memory); > -- > 2.19.0.397.gdd90340f6a-goog >
On Fri, Sep 21, 2018 at 1:37 PM, Dmitry Vyukov <dvyukov@google.com> wrote: > On Wed, Sep 19, 2018 at 8:54 PM, Andrey Konovalov <andreyknvl@google.com> wrote: >> + /* >> + * Since it's desirable to only call object contructors ones during > > s/ones/once/ Will fix. > >> + * slab allocation, we preassign tags to all such objects. > > While we are here, it can make sense to mention that we can't repaint > objects with ctors after reallocation (even for > non-SLAB_TYPESAFE_BY_RCU) because the ctor code can memorize pointer > to the object somewhere (e.g. in the object itself). Then if we > repaint it, the old memorized pointer will become invalid. Will mention. >> - kasan_unpoison_shadow(object, size); >> + /* See the comment in kasan_init_slab_obj regarding preassigned tags */ >> + if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) && >> + (cache->ctor || cache->flags & SLAB_TYPESAFE_BY_RCU)) { >> +#ifdef CONFIG_SLAB >> + struct page *page = virt_to_page(object); >> + >> + tag = (u8)obj_to_index(cache, page, (void *)object); >> +#else >> + tag = get_tag(object); >> +#endif > > This kinda _almost_ matches the chunk of code in kasan_init_slab_obj, > but not exactly. Wonder if there is some nice way to unify this code? > > Maybe something like: > > static u8 tag_for_object(struct kmem_cache *cache, const void *object, new bool) > { > if (!IS_ENABLED(CONFIG_KASAN_SW_TAGS) || > !cache->ctor && !(cache->flags & SLAB_TYPESAFE_BY_RCU)) > return random_tag(); > #ifdef CONFIG_SLAB > struct page *page = virt_to_page(object); > return (u8)obj_to_index(cache, page, (void *)object); > #else > return new ? random_tag() : get_tag(object); > #endif > } > > Then we can call this in both places. Will do, however I think it's better to do the CONFIG_KASAN_SW_TAGS check outside this helper function. > As a side effect this will assign tags to pointers during slab > initialization even if we don't have ctors, but it should be fine (?). We don't have to assign tag in this case, can just leave 0xff.
diff --git a/mm/kasan/common.c b/mm/kasan/common.c index 7134e75447ff..d368095feb6c 100644 --- a/mm/kasan/common.c +++ b/mm/kasan/common.c @@ -140,6 +140,13 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value) { void *shadow_start, *shadow_end; + /* + * Perform shadow offset calculation based on untagged address, as + * some of the callers (e.g. kasan_poison_object_data) pass tagged + * addresses to this function. + */ + address = reset_tag(address); + shadow_start = kasan_mem_to_shadow(address); shadow_end = kasan_mem_to_shadow(address + size); @@ -148,11 +155,24 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value) void kasan_unpoison_shadow(const void *address, size_t size) { - kasan_poison_shadow(address, size, 0); + u8 tag = get_tag(address); + + /* + * Perform shadow offset calculation based on untagged address, as + * some of the callers (e.g. kasan_unpoison_object_data) pass tagged + * addresses to this function. + */ + address = reset_tag(address); + + kasan_poison_shadow(address, size, tag); if (size & KASAN_SHADOW_MASK) { u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size); - *shadow = size & KASAN_SHADOW_MASK; + + if (IS_ENABLED(CONFIG_KASAN_SW_TAGS)) + *shadow = tag; + else + *shadow = size & KASAN_SHADOW_MASK; } } @@ -200,8 +220,9 @@ void kasan_unpoison_stack_above_sp_to(const void *watermark) void kasan_alloc_pages(struct page *page, unsigned int order) { - if (likely(!PageHighMem(page))) - kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order); + if (unlikely(PageHighMem(page))) + return; + kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order); } void kasan_free_pages(struct page *page, unsigned int order) @@ -218,6 +239,9 @@ void kasan_free_pages(struct page *page, unsigned int order) */ static inline unsigned int optimal_redzone(unsigned int object_size) { + if (IS_ENABLED(CONFIG_KASAN_SW_TAGS)) + return 0; + return object_size <= 64 - 16 ? 16 : object_size <= 128 - 32 ? 32 : @@ -232,6 +256,7 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size, slab_flags_t *flags) { unsigned int orig_size = *size; + unsigned int redzone_size; int redzone_adjust; /* Add alloc meta. */ @@ -239,20 +264,20 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size, *size += sizeof(struct kasan_alloc_meta); /* Add free meta. */ - if (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor || - cache->object_size < sizeof(struct kasan_free_meta)) { + if (IS_ENABLED(CONFIG_KASAN_GENERIC) && + (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor || + cache->object_size < sizeof(struct kasan_free_meta))) { cache->kasan_info.free_meta_offset = *size; *size += sizeof(struct kasan_free_meta); } - redzone_adjust = optimal_redzone(cache->object_size) - - (*size - cache->object_size); + redzone_size = optimal_redzone(cache->object_size); + redzone_adjust = redzone_size - (*size - cache->object_size); if (redzone_adjust > 0) *size += redzone_adjust; *size = min_t(unsigned int, KMALLOC_MAX_SIZE, - max(*size, cache->object_size + - optimal_redzone(cache->object_size))); + max(*size, cache->object_size + redzone_size)); /* * If the metadata doesn't fit, don't enable KASAN at all. @@ -265,6 +290,8 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size, return; } + cache->align = round_up(cache->align, KASAN_SHADOW_SCALE_SIZE); + *flags |= SLAB_KASAN; } @@ -319,6 +346,28 @@ void *kasan_init_slab_obj(struct kmem_cache *cache, const void *object) alloc_info = get_alloc_info(cache, object); __memset(alloc_info, 0, sizeof(*alloc_info)); + /* + * Since it's desirable to only call object contructors ones during + * slab allocation, we preassign tags to all such objects. + * Also preassign tags for SLAB_TYPESAFE_BY_RCU slabs to avoid + * use-after-free reports. + * For SLAB allocator we can't preassign tags randomly since the + * freelist is stored as an array of indexes instead of a linked + * list. Assign tags based on objects indexes, so that objects that + * are next to each other get different tags. + */ + if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) && + (cache->ctor || cache->flags & SLAB_TYPESAFE_BY_RCU)) { +#ifdef CONFIG_SLAB + struct page *page = virt_to_page(object); + u8 tag = (u8)obj_to_index(cache, page, (void *)object); +#else + u8 tag = random_tag(); +#endif + + object = set_tag(object, tag); + } + return (void *)object; } @@ -327,15 +376,30 @@ void *kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags) return kasan_kmalloc(cache, object, cache->object_size, flags); } +static inline bool shadow_invalid(u8 tag, s8 shadow_byte) +{ + if (IS_ENABLED(CONFIG_KASAN_GENERIC)) + return shadow_byte < 0 || + shadow_byte >= KASAN_SHADOW_SCALE_SIZE; + else + return tag != (u8)shadow_byte; +} + static bool __kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip, bool quarantine) { s8 shadow_byte; + u8 tag; + void *tagged_object; unsigned long rounded_up_size; + tag = get_tag(object); + tagged_object = object; + object = reset_tag(object); + if (unlikely(nearest_obj(cache, virt_to_head_page(object), object) != object)) { - kasan_report_invalid_free(object, ip); + kasan_report_invalid_free(tagged_object, ip); return true; } @@ -344,20 +408,22 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object, return false; shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object)); - if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) { - kasan_report_invalid_free(object, ip); + if (shadow_invalid(tag, shadow_byte)) { + kasan_report_invalid_free(tagged_object, ip); return true; } rounded_up_size = round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE); kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE); - if (!quarantine || unlikely(!(cache->flags & SLAB_KASAN))) + if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) || + unlikely(!(cache->flags & SLAB_KASAN))) return false; set_track(&get_alloc_info(cache, object)->free_track, GFP_NOWAIT); quarantine_put(get_free_info(cache, object), cache); - return true; + + return IS_ENABLED(CONFIG_KASAN_GENERIC); } bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip) @@ -370,6 +436,7 @@ void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size, { unsigned long redzone_start; unsigned long redzone_end; + u8 tag; if (gfpflags_allow_blocking(flags)) quarantine_reduce(); @@ -382,14 +449,27 @@ void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size, redzone_end = round_up((unsigned long)object + cache->object_size, KASAN_SHADOW_SCALE_SIZE); - kasan_unpoison_shadow(object, size); + /* See the comment in kasan_init_slab_obj regarding preassigned tags */ + if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) && + (cache->ctor || cache->flags & SLAB_TYPESAFE_BY_RCU)) { +#ifdef CONFIG_SLAB + struct page *page = virt_to_page(object); + + tag = (u8)obj_to_index(cache, page, (void *)object); +#else + tag = get_tag(object); +#endif + } else + tag = random_tag(); + + kasan_unpoison_shadow(set_tag(object, tag), size); kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start, KASAN_KMALLOC_REDZONE); if (cache->flags & SLAB_KASAN) set_track(&get_alloc_info(cache, object)->alloc_track, flags); - return (void *)object; + return set_tag(object, tag); } EXPORT_SYMBOL(kasan_kmalloc); @@ -439,7 +519,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip) page = virt_to_head_page(ptr); if (unlikely(!PageSlab(page))) { - if (ptr != page_address(page)) { + if (reset_tag(ptr) != page_address(page)) { kasan_report_invalid_free(ptr, ip); return; } @@ -452,7 +532,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip) void kasan_kfree_large(void *ptr, unsigned long ip) { - if (ptr != page_address(virt_to_head_page(ptr))) + if (reset_tag(ptr) != page_address(virt_to_head_page(ptr))) kasan_report_invalid_free(ptr, ip); /* The object will be poisoned by page_alloc. */ } diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h index a2533b890248..a3db6b8efe7a 100644 --- a/mm/kasan/kasan.h +++ b/mm/kasan/kasan.h @@ -12,10 +12,18 @@ #define KASAN_TAG_INVALID 0xFE /* inaccessible memory tag */ #define KASAN_TAG_MAX 0xFD /* maximum value for random tags */ +#ifdef CONFIG_KASAN_GENERIC #define KASAN_FREE_PAGE 0xFF /* page was freed */ #define KASAN_PAGE_REDZONE 0xFE /* redzone for kmalloc_large allocations */ #define KASAN_KMALLOC_REDZONE 0xFC /* redzone inside slub object */ #define KASAN_KMALLOC_FREE 0xFB /* object was freed (kmem_cache_free/kfree) */ +#else +#define KASAN_FREE_PAGE KASAN_TAG_INVALID +#define KASAN_PAGE_REDZONE KASAN_TAG_INVALID +#define KASAN_KMALLOC_REDZONE KASAN_TAG_INVALID +#define KASAN_KMALLOC_FREE KASAN_TAG_INVALID +#endif + #define KASAN_GLOBAL_REDZONE 0xFA /* redzone for global variable */ /* diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c index 700323946867..a3cca11e4fed 100644 --- a/mm/kasan/tags.c +++ b/mm/kasan/tags.c @@ -78,15 +78,60 @@ void *kasan_reset_tag(const void *addr) void check_memory_region(unsigned long addr, size_t size, bool write, unsigned long ret_ip) { + u8 tag; + u8 *shadow_first, *shadow_last, *shadow; + void *untagged_addr; + + if (unlikely(size == 0)) + return; + + tag = get_tag((const void *)addr); + + /* + * Ignore accesses for pointers tagged with 0xff (native kernel + * pointer tag) to suppress false positives caused by kmap. + * + * Some kernel code was written to account for archs that don't keep + * high memory mapped all the time, but rather map and unmap particular + * pages when needed. Instead of storing a pointer to the kernel memory, + * this code saves the address of the page structure and offset within + * that page for later use. Those pages are then mapped and unmapped + * with kmap/kunmap when necessary and virt_to_page is used to get the + * virtual address of the page. For arm64 (that keeps the high memory + * mapped all the time), kmap is turned into a page_address call. + + * The issue is that with use of the page_address + virt_to_page + * sequence the top byte value of the original pointer gets lost (gets + * set to KASAN_TAG_KERNEL (0xFF)). + */ + if (tag == KASAN_TAG_KERNEL) + return; + + untagged_addr = reset_tag((const void *)addr); + if (unlikely(untagged_addr < + kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) { + kasan_report(addr, size, write, ret_ip); + return; + } + shadow_first = kasan_mem_to_shadow(untagged_addr); + shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1); + for (shadow = shadow_first; shadow <= shadow_last; shadow++) { + if (*shadow != tag) { + kasan_report(addr, size, write, ret_ip); + return; + } + } } #define DEFINE_HWASAN_LOAD_STORE(size) \ void __hwasan_load##size##_noabort(unsigned long addr) \ { \ + check_memory_region(addr, size, false, _RET_IP_); \ } \ EXPORT_SYMBOL(__hwasan_load##size##_noabort); \ void __hwasan_store##size##_noabort(unsigned long addr) \ { \ + check_memory_region(addr, size, true, _RET_IP_); \ } \ EXPORT_SYMBOL(__hwasan_store##size##_noabort) @@ -98,15 +143,18 @@ DEFINE_HWASAN_LOAD_STORE(16); void __hwasan_loadN_noabort(unsigned long addr, unsigned long size) { + check_memory_region(addr, size, false, _RET_IP_); } EXPORT_SYMBOL(__hwasan_loadN_noabort); void __hwasan_storeN_noabort(unsigned long addr, unsigned long size) { + check_memory_region(addr, size, true, _RET_IP_); } EXPORT_SYMBOL(__hwasan_storeN_noabort); void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size) { + kasan_poison_shadow((void *)addr, size, tag); } EXPORT_SYMBOL(__hwasan_tag_memory);
This commit adds tag-based KASAN specific hooks implementation and adjusts common generic and tag-based KASAN ones. 1. When a new slab cache is created, tag-based KASAN rounds up the size of the objects in this cache to KASAN_SHADOW_SCALE_SIZE (== 16). 2. On each kmalloc tag-based KASAN generates a random tag, sets the shadow memory, that corresponds to this object to this tag, and embeds this tag value into the top byte of the returned pointer. 3. On each kfree tag-based KASAN poisons the shadow memory with a random tag to allow detection of use-after-free bugs. The rest of the logic of the hook implementation is very much similar to the one provided by generic KASAN. Tag-based KASAN saves allocation and free stack metadata to the slab object the same way generic KASAN does. Signed-off-by: Andrey Konovalov <andreyknvl@google.com> --- mm/kasan/common.c | 118 ++++++++++++++++++++++++++++++++++++++-------- mm/kasan/kasan.h | 8 ++++ mm/kasan/tags.c | 48 +++++++++++++++++++ 3 files changed, 155 insertions(+), 19 deletions(-)