Allocation requests with __GFP_DMA/__GFP_DMA32 or SLAB_CACHE_DMA/SLAB_CACHE_DMA32 cannot be fulfilled by KFENCE, because they must reside in low memory, whereas KFENCE memory pool is located in high memory.

Skip such allocations to avoid crashes where DMAable memory is expected.

Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure") Cc: Andrew Morton akpm@linux-foundation.org Cc: Dmitry Vyukov dvyukov@google.com Cc: Marco Elver elver@google.com Cc: stable@vger.kernel.org # 5.12+ Signed-off-by: Alexander Potapenko glider@google.com --- mm/kfence/core.c | 8 ++++++++ 1 file changed, 8 insertions(+)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c index 4d21ac44d5d35..fd70089bd2808 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -760,6 +760,14 @@ void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) if (size > PAGE_SIZE) return NULL;

+ /* + * Skip DMA allocations. These must reside in the low memory, which we + * cannot guarantee. + */ + if (flags & (__GFP_DMA | __GFP_DMA32) || + (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32))) + return NULL; + return kfence_guarded_alloc(s, size, flags); }