From: Alexander Potapenko glider@google.com Subject: 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 ---

mm/kfence/core.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/mm/kfence/core.c~kfence-move-the-size-check-to-the-beginning-of-__kfence_alloc +++ a/mm/kfence/core.c @@ -734,6 +734,13 @@ void kfence_shutdown_cache(struct kmem_c 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 * cost, in case we have a large number of concurrent allocations. @@ -757,9 +764,6 @@ void *__kfence_alloc(struct kmem_cache * if (!READ_ONCE(kfence_enabled)) return NULL;

- if (size > PAGE_SIZE) - return NULL; - return kfence_guarded_alloc(s, size, flags); }

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