On Thu, Oct 22, 2020 at 3:20 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote: > > Since kasan_kmalloc() always follows kasan_slab_alloc(), there's no need > to reunpoison the object data, only to poison the redzone. > > This requires changing kasan annotation for early SLUB cache to > kasan_slab_alloc(). Otherwise kasan_kmalloc() doesn't untag the object. > This doesn't do any functional changes, as kmem_cache_node->object_size > is equal to sizeof(struct kmem_cache_node). > > Similarly for kasan_krealloc(), as it's called after ksize(), which > already unpoisoned the object, there's no need to do it again. Have you considered doing this the other way around: make krealloc call __ksize and unpoison in kasan_krealloc? This has the advantage of more precise poisoning as ksize will unpoison the whole underlying object. But then maybe we will need to move first checks in ksize into __ksize as we may need them in krealloc as well. > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> > Link: https://linux-review.googlesource.com/id/I4083d3b55605f70fef79bca9b90843c4390296f2 > --- > mm/kasan/common.c | 31 +++++++++++++++++++++---------- > mm/slub.c | 3 +-- > 2 files changed, 22 insertions(+), 12 deletions(-) > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index c5ec60e1a4d2..a581937c2a44 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -360,8 +360,14 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object, > if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) || IS_ENABLED(CONFIG_KASAN_HW_TAGS)) > tag = assign_tag(cache, object, false, keep_tag); > > - /* Tag is ignored in set_tag without CONFIG_KASAN_SW/HW_TAGS */ > - kasan_unpoison_memory(set_tag(object, tag), size); > + /* > + * Don't unpoison the object when keeping the tag. Tag is kept for: > + * 1. krealloc(), and then the memory has already been unpoisoned via ksize(); > + * 2. kmalloc(), and then the memory has already been unpoisoned by kasan_kmalloc(). > + * Tag is ignored in set_tag() without CONFIG_KASAN_SW/HW_TAGS. > + */ > + if (!keep_tag) > + kasan_unpoison_memory(set_tag(object, tag), size); > kasan_poison_memory((void *)redzone_start, redzone_end - redzone_start, > KASAN_KMALLOC_REDZONE); > > @@ -384,10 +390,9 @@ void * __must_check __kasan_kmalloc(struct kmem_cache *cache, const void *object > } > EXPORT_SYMBOL(__kasan_kmalloc); > > -void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size, > - gfp_t flags) > +static void * __must_check ____kasan_kmalloc_large(struct page *page, const void *ptr, > + size_t size, gfp_t flags, bool realloc) > { > - struct page *page; > unsigned long redzone_start; > unsigned long redzone_end; > > @@ -397,18 +402,24 @@ void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size, > if (unlikely(ptr == NULL)) > return NULL; > > - page = virt_to_page(ptr); > - redzone_start = round_up((unsigned long)(ptr + size), > - KASAN_GRANULE_SIZE); > + redzone_start = round_up((unsigned long)(ptr + size), KASAN_GRANULE_SIZE); > redzone_end = (unsigned long)ptr + page_size(page); > > - kasan_unpoison_memory(ptr, size); > + /* ksize() in __do_krealloc() already unpoisoned the memory. */ > + if (!realloc) > + kasan_unpoison_memory(ptr, size); > kasan_poison_memory((void *)redzone_start, redzone_end - redzone_start, > KASAN_PAGE_REDZONE); > > return (void *)ptr; > } > > +void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size, > + gfp_t flags) > +{ > + return ____kasan_kmalloc_large(virt_to_page(ptr), ptr, size, flags, false); > +} > + > void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flags) > { > struct page *page; > @@ -419,7 +430,7 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag > page = virt_to_head_page(object); > > if (unlikely(!PageSlab(page))) > - return __kasan_kmalloc_large(object, size, flags); > + return ____kasan_kmalloc_large(page, object, size, flags, true); > else > return ____kasan_kmalloc(page->slab_cache, object, size, > flags, true); > diff --git a/mm/slub.c b/mm/slub.c > index 1d3f2355df3b..afb035b0bf2d 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -3535,8 +3535,7 @@ static void early_kmem_cache_node_alloc(int node) > init_object(kmem_cache_node, n, SLUB_RED_ACTIVE); > init_tracking(kmem_cache_node, n); > #endif > - n = kasan_kmalloc(kmem_cache_node, n, sizeof(struct kmem_cache_node), > - GFP_KERNEL); > + n = kasan_slab_alloc(kmem_cache_node, n, GFP_KERNEL); > page->freelist = get_freepointer(kmem_cache_node, n); > page->inuse = 1; > page->frozen = 0; > -- > 2.29.0.rc1.297.gfa9743e501-goog >
