[PATCH] kfence: skip DMA allocations

[PATCH] kfence: skip DMA allocations

[Alexander Potapenko]

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);
 }
 
-- 
2.32.0.93.g670b81a890-goog

[PATCH] kfence: skip DMA allocations

[Alexander Potapenko]

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);
 }
 
-- 
2.32.0.93.g670b81a890-goog

Re: [PATCH] kfence: skip DMA allocations

[Marco Elver]

On Tue, 29 Jun 2021 at 15:00, Alexander Potapenko <glider@google.com> wrote:
[...]
> +       /*
> +        * Skip DMA allocations. These must reside in the low memory, which we
> +        * cannot guarantee.
> +        */
> +       if (flags & (__GFP_DMA | __GFP_DMA32) ||

I think we want braces around "flags & (...)", so that this becomes:

    if ((flags & (...)) ||

> +           (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32)))
> +               return NULL;

Thanks,
-- Marco

Re: [PATCH] kfence: skip DMA allocations

[Marco Elver]

On Tue, 29 Jun 2021 at 15:00, Alexander Potapenko <glider@google.com> wrote:
[...]
> +       /*
> +        * Skip DMA allocations. These must reside in the low memory, which we
> +        * cannot guarantee.
> +        */
> +       if (flags & (__GFP_DMA | __GFP_DMA32) ||

I think we want braces around "flags & (...)", so that this becomes:

    if ((flags & (...)) ||

> +           (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32)))
> +               return NULL;

Thanks,
-- Marco