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kfence: always use static branches to guard kfence_alloc()

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Regardless of KFENCE mode (CONFIG_KFENCE_STATIC_KEYS: either using
static keys to gate allocations, or using a simple dynamic branch),
always use a static branch to avoid the dynamic branch in kfence_alloc()
if KFENCE was disabled at boot.

For CONFIG_KFENCE_STATIC_KEYS=n, this now avoids the dynamic branch if
KFENCE was disabled at boot.

To simplify, also unifies the location where kfence_allocation_gate is
read-checked to just be inline in kfence_alloc().

Link: https://lkml.kernel.org/r/20211019102524.2807208-1-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Marco Elver 2021-11-05 13:45:46 -07:00 • committed by Linus Torvalds
parent 4933295622
commit 07e8481d3c
2 changed files with 18 additions and 19 deletions
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21
include/linux/kfence.h
View file

@ -14,6 +14,9 @@
#ifdef CONFIG_KFENCE
#include <linux/atomic.h>
#include <linux/static_key.h>
/*
* We allocate an even number of pages, as it simplifies calculations to map
* address to metadata indices; effectively, the very first page serves as an
@ -22,13 +25,8 @@
#define KFENCE_POOL_SIZE ((CONFIG_KFENCE_NUM_OBJECTS + 1) * 2 * PAGE_SIZE)
extern char *__kfence_pool;
#ifdef CONFIG_KFENCE_STATIC_KEYS
#include <linux/static_key.h>
DECLARE_STATIC_KEY_FALSE(kfence_allocation_key);
#else
#include <linux/atomic.h>
extern atomic_t kfence_allocation_gate;
#endif
/**
* is_kfence_address() - check if an address belongs to KFENCE pool
@ -116,13 +114,16 @@ void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags);
*/
static __always_inline void *kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
{
#ifdef CONFIG_KFENCE_STATIC_KEYS
if (static_branch_unlikely(&kfence_allocation_key))
#if defined(CONFIG_KFENCE_STATIC_KEYS) || CONFIG_KFENCE_SAMPLE_INTERVAL == 0
if (!static_branch_unlikely(&kfence_allocation_key))
return NULL;
#else
if (unlikely(!atomic_read(&kfence_allocation_gate)))
if (!static_branch_likely(&kfence_allocation_key))
return NULL;
#endif
return __kfence_alloc(s, size, flags);
return NULL;
if (likely(atomic_read(&kfence_allocation_gate)))
return NULL;
return __kfence_alloc(s, size, flags);
}
/**