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FROMLIST: kfence: move the size check to the beginning of __kfence_alloc()

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Check the allocation size before toggling kfence_allocation_gate.
This way allocations that can't be served by KFENCE will not result in
waiting for another CONFIG_KFENCE_SAMPLE_INTERVAL without allocating
anything.

Suggested-by: Marco Elver <elver@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: stable@vger.kernel.org # 5.12+
Signed-off-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Marco Elver <elver@google.com>

Bug: 192294212
Test: ran KFENCE test suite with __GFP_DMA on QEMU
Link: https://lore.kernel.org/linux-mm/20210714092222.1890268-1-glider@google.com/
Change-Id: Ie69c6134fc1c3e68238457b146e26355c17f5295
Signed-off-by: Alexander Potapenko <glider@google.com>
This commit is contained in:
Alexander Potapenko
2021-06-30 11:50:11 +02:00
parent ddabf14bea
commit 8478d8dc53
1 changed files with 7 additions and 3 deletions
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10
mm/kfence/core.c
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@@ -733,6 +733,13 @@ void kfence_shutdown_cache(struct kmem_cache *s)
void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
{
/*
* Perform size check before switching kfence_allocation_gate, so that
* we don't disable KFENCE without making an allocation.
*/
if (size > PAGE_SIZE)
return NULL;
/*
* allocation_gate only needs to become non-zero, so it doesn't make
* sense to continue writing to it and pay the associated contention
@@ -757,9 +764,6 @@ void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
if (!READ_ONCE(kfence_enabled))
return NULL;
if (size > PAGE_SIZE)
return NULL;
return kfence_guarded_alloc(s, size, flags);
}