| Message ID | 20240724-kasan-tsbrcu-v2-1-45f898064468@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | allow KASAN to detect UAF in SLAB_TYPESAFE_BY_RCU slabs | expand |
On Wed, 24 Jul 2024 18:34:12 +0200 Jann Horn <jannh@google.com> wrote: > Currently, when KASAN is combined with init-on-free behavior, the > initialization happens before KASAN's "invalid free" checks. > > More importantly, a subsequent commit will want to use the object metadata > region to store an rcu_head, and we should let KASAN check that the object > pointer is valid before that. (Otherwise that change will make the existing > testcase kmem_cache_invalid_free fail.) > > So add a new KASAN hook that allows KASAN to pre-validate a > kmem_cache_free() operation before SLUB actually starts modifying the > object or its metadata. I added this, to fix the CONFIG_KASAN=n build --- a/include/linux/kasan.h~kasan-catch-invalid-free-before-slub-reinitializes-the-object-fix +++ a/include/linux/kasan.h @@ -381,6 +381,12 @@ static inline void *kasan_init_slab_obj( { return (void *)object; } + +static inline bool kasan_slab_pre_free(struct kmem_cache *s, void *object) +{ + return false; +} + static inline bool kasan_slab_free(struct kmem_cache *s, void *object, bool init) { return false;
On Wed, Jul 24, 2024 at 11:17 PM Andrew Morton <akpm@linux-foundation.org> wrote: > On Wed, 24 Jul 2024 18:34:12 +0200 Jann Horn <jannh@google.com> wrote: > > > Currently, when KASAN is combined with init-on-free behavior, the > > initialization happens before KASAN's "invalid free" checks. > > > > More importantly, a subsequent commit will want to use the object metadata > > region to store an rcu_head, and we should let KASAN check that the object > > pointer is valid before that. (Otherwise that change will make the existing > > testcase kmem_cache_invalid_free fail.) > > > > So add a new KASAN hook that allows KASAN to pre-validate a > > kmem_cache_free() operation before SLUB actually starts modifying the > > object or its metadata. > > I added this, to fix the CONFIG_KASAN=n build Whoops, thanks for fixing that up.
On 7/24/24 6:34 PM, Jann Horn wrote: > Currently, when KASAN is combined with init-on-free behavior, the > initialization happens before KASAN's "invalid free" checks. > > More importantly, a subsequent commit will want to use the object metadata > region to store an rcu_head, and we should let KASAN check that the object > pointer is valid before that. (Otherwise that change will make the existing > testcase kmem_cache_invalid_free fail.) > > So add a new KASAN hook that allows KASAN to pre-validate a > kmem_cache_free() operation before SLUB actually starts modifying the > object or its metadata. > > Signed-off-by: Jann Horn <jannh@google.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> #slub > --- > include/linux/kasan.h | 10 ++++++++++ > mm/kasan/common.c | 51 +++++++++++++++++++++++++++++++++++++++------------ > mm/slub.c | 7 +++++++ > 3 files changed, 56 insertions(+), 12 deletions(-) > > diff --git a/include/linux/kasan.h b/include/linux/kasan.h > index 70d6a8f6e25d..eee8ca1dcb40 100644 > --- a/include/linux/kasan.h > +++ b/include/linux/kasan.h > @@ -175,6 +175,16 @@ static __always_inline void * __must_check kasan_init_slab_obj( > return (void *)object; > } > > +bool __kasan_slab_pre_free(struct kmem_cache *s, void *object, > + unsigned long ip); > +static __always_inline bool kasan_slab_pre_free(struct kmem_cache *s, > + void *object) > +{ > + if (kasan_enabled()) > + return __kasan_slab_pre_free(s, object, _RET_IP_); > + return false; > +} > + > bool __kasan_slab_free(struct kmem_cache *s, void *object, > unsigned long ip, bool init); > static __always_inline bool kasan_slab_free(struct kmem_cache *s, > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index 85e7c6b4575c..7c7fc6ce7eb7 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -208,31 +208,52 @@ void * __must_check __kasan_init_slab_obj(struct kmem_cache *cache, > return (void *)object; > } > > -static inline bool poison_slab_object(struct kmem_cache *cache, void *object, > - unsigned long ip, bool init) > +enum free_validation_result { > + KASAN_FREE_IS_IGNORED, > + KASAN_FREE_IS_VALID, > + KASAN_FREE_IS_INVALID > +}; > + > +static enum free_validation_result check_slab_free(struct kmem_cache *cache, > + void *object, unsigned long ip) > { > - void *tagged_object; > + void *tagged_object = object; > > - if (!kasan_arch_is_ready()) > - return false; > + if (is_kfence_address(object) || !kasan_arch_is_ready()) > + return KASAN_FREE_IS_IGNORED; > > - tagged_object = object; > object = kasan_reset_tag(object); > > if (unlikely(nearest_obj(cache, virt_to_slab(object), object) != object)) { > kasan_report_invalid_free(tagged_object, ip, KASAN_REPORT_INVALID_FREE); > - return true; > + return KASAN_FREE_IS_INVALID; > } > > - /* RCU slabs could be legally used after free within the RCU period. */ > - if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU)) > - return false; > - > if (!kasan_byte_accessible(tagged_object)) { > kasan_report_invalid_free(tagged_object, ip, KASAN_REPORT_DOUBLE_FREE); > - return true; > + return KASAN_FREE_IS_INVALID; > } > > + return KASAN_FREE_IS_VALID; > +} > + > +static inline bool poison_slab_object(struct kmem_cache *cache, void *object, > + unsigned long ip, bool init) > +{ > + void *tagged_object = object; > + enum free_validation_result valid = check_slab_free(cache, object, ip); > + > + if (valid == KASAN_FREE_IS_IGNORED) > + return false; > + if (valid == KASAN_FREE_IS_INVALID) > + return true; > + > + object = kasan_reset_tag(object); > + > + /* RCU slabs could be legally used after free within the RCU period. */ > + if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU)) > + return false; > + > kasan_poison(object, round_up(cache->object_size, KASAN_GRANULE_SIZE), > KASAN_SLAB_FREE, init); > > @@ -242,6 +263,12 @@ static inline bool poison_slab_object(struct kmem_cache *cache, void *object, > return false; > } > > +bool __kasan_slab_pre_free(struct kmem_cache *cache, void *object, > + unsigned long ip) > +{ > + return check_slab_free(cache, object, ip) == KASAN_FREE_IS_INVALID; > +} > + > bool __kasan_slab_free(struct kmem_cache *cache, void *object, > unsigned long ip, bool init) > { > diff --git a/mm/slub.c b/mm/slub.c > index 4927edec6a8c..34724704c52d 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2170,6 +2170,13 @@ bool slab_free_hook(struct kmem_cache *s, void *x, bool init) > if (kfence_free(x)) > return false; > > + /* > + * Give KASAN a chance to notice an invalid free operation before we > + * modify the object. > + */ > + if (kasan_slab_pre_free(s, x)) > + return false; > + > /* > * As memory initialization might be integrated into KASAN, > * kasan_slab_free and initialization memset's must be >
diff --git a/include/linux/kasan.h b/include/linux/kasan.h index 70d6a8f6e25d..eee8ca1dcb40 100644 --- a/include/linux/kasan.h +++ b/include/linux/kasan.h @@ -175,6 +175,16 @@ static __always_inline void * __must_check kasan_init_slab_obj( return (void *)object; } +bool __kasan_slab_pre_free(struct kmem_cache *s, void *object, + unsigned long ip); +static __always_inline bool kasan_slab_pre_free(struct kmem_cache *s, + void *object) +{ + if (kasan_enabled()) + return __kasan_slab_pre_free(s, object, _RET_IP_); + return false; +} + bool __kasan_slab_free(struct kmem_cache *s, void *object, unsigned long ip, bool init); static __always_inline bool kasan_slab_free(struct kmem_cache *s, diff --git a/mm/kasan/common.c b/mm/kasan/common.c index 85e7c6b4575c..7c7fc6ce7eb7 100644 --- a/mm/kasan/common.c +++ b/mm/kasan/common.c @@ -208,31 +208,52 @@ void * __must_check __kasan_init_slab_obj(struct kmem_cache *cache, return (void *)object; } -static inline bool poison_slab_object(struct kmem_cache *cache, void *object, - unsigned long ip, bool init) +enum free_validation_result { + KASAN_FREE_IS_IGNORED, + KASAN_FREE_IS_VALID, + KASAN_FREE_IS_INVALID +}; + +static enum free_validation_result check_slab_free(struct kmem_cache *cache, + void *object, unsigned long ip) { - void *tagged_object; + void *tagged_object = object; - if (!kasan_arch_is_ready()) - return false; + if (is_kfence_address(object) || !kasan_arch_is_ready()) + return KASAN_FREE_IS_IGNORED; - tagged_object = object; object = kasan_reset_tag(object); if (unlikely(nearest_obj(cache, virt_to_slab(object), object) != object)) { kasan_report_invalid_free(tagged_object, ip, KASAN_REPORT_INVALID_FREE); - return true; + return KASAN_FREE_IS_INVALID; } - /* RCU slabs could be legally used after free within the RCU period. */ - if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU)) - return false; - if (!kasan_byte_accessible(tagged_object)) { kasan_report_invalid_free(tagged_object, ip, KASAN_REPORT_DOUBLE_FREE); - return true; + return KASAN_FREE_IS_INVALID; } + return KASAN_FREE_IS_VALID; +} + +static inline bool poison_slab_object(struct kmem_cache *cache, void *object, + unsigned long ip, bool init) +{ + void *tagged_object = object; + enum free_validation_result valid = check_slab_free(cache, object, ip); + + if (valid == KASAN_FREE_IS_IGNORED) + return false; + if (valid == KASAN_FREE_IS_INVALID) + return true; + + object = kasan_reset_tag(object); + + /* RCU slabs could be legally used after free within the RCU period. */ + if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU)) + return false; + kasan_poison(object, round_up(cache->object_size, KASAN_GRANULE_SIZE), KASAN_SLAB_FREE, init); @@ -242,6 +263,12 @@ static inline bool poison_slab_object(struct kmem_cache *cache, void *object, return false; } +bool __kasan_slab_pre_free(struct kmem_cache *cache, void *object, + unsigned long ip) +{ + return check_slab_free(cache, object, ip) == KASAN_FREE_IS_INVALID; +} + bool __kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip, bool init) { diff --git a/mm/slub.c b/mm/slub.c index 4927edec6a8c..34724704c52d 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2170,6 +2170,13 @@ bool slab_free_hook(struct kmem_cache *s, void *x, bool init) if (kfence_free(x)) return false; + /* + * Give KASAN a chance to notice an invalid free operation before we + * modify the object. + */ + if (kasan_slab_pre_free(s, x)) + return false; + /* * As memory initialization might be integrated into KASAN, * kasan_slab_free and initialization memset's must be
Currently, when KASAN is combined with init-on-free behavior, the initialization happens before KASAN's "invalid free" checks. More importantly, a subsequent commit will want to use the object metadata region to store an rcu_head, and we should let KASAN check that the object pointer is valid before that. (Otherwise that change will make the existing testcase kmem_cache_invalid_free fail.) So add a new KASAN hook that allows KASAN to pre-validate a kmem_cache_free() operation before SLUB actually starts modifying the object or its metadata. Signed-off-by: Jann Horn <jannh@google.com> --- include/linux/kasan.h | 10 ++++++++++ mm/kasan/common.c | 51 +++++++++++++++++++++++++++++++++++++++------------ mm/slub.c | 7 +++++++ 3 files changed, 56 insertions(+), 12 deletions(-)