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

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.

Link: https://lkml.kernel.org/r/20210714092222.1890268-1-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Suggested-by: Marco Elver <elver@google.com>
Reviewed-by: Marco Elver <elver@google.com>
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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Alexander Potapenko 2021-07-23 15:50:11 -07:00 committed by Linus Torvalds
parent 32ae8a0669
commit 235a85cb32
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) 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 * allocation_gate only needs to become non-zero, so it doesn't make
* sense to continue writing to it and pay the associated contention * 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)) if (!READ_ONCE(kfence_enabled))
return NULL; return NULL;
if (size > PAGE_SIZE)
return NULL;
return kfence_guarded_alloc(s, size, flags); return kfence_guarded_alloc(s, size, flags);
} }