Commit fd25d19f authored by Kees Cook's avatar Kees Cook Committed by Ingo Molnar
Browse files

locking/refcount: Create unchecked atomic_t implementation

Many subsystems will not use refcount_t unless there is a way to build the
kernel so that there is no regression in speed compared to atomic_t. This
adds CONFIG_REFCOUNT_FULL to enable the full refcount_t implementation
which has the validation but is slightly slower. When not enabled,
refcount_t uses the basic unchecked atomic_t routines, which results in
no code changes compared to just using atomic_t directly.

Signed-off-by: default avatarKees Cook <>
Acked-by: default avatarGreg Kroah-Hartman <>
Cc: Alexey Dobriyan <>
Cc: Andrew Morton <>
Cc: Arnd Bergmann <>
Cc: Christoph Hellwig <>
Cc: David S. Miller <>
Cc: David Windsor <>
Cc: Davidlohr Bueso <>
Cc: Elena Reshetova <>
Cc: Eric Biggers <>
Cc: Eric W. Biederman <>
Cc: Hans Liljestra...
parent f9e16988
......@@ -867,4 +867,13 @@ config STRICT_MODULE_RWX
bool "Perform full reference count validation at the expense of speed"
Enabling this switches the refcounting infrastructure from a fast
unchecked atomic_t implementation to a fully state checked
implementation, which can be (slightly) slower but provides protections
against various use-after-free conditions that can be used in
security flaw exploits.
source "kernel/gcov/Kconfig"
......@@ -41,6 +41,7 @@ static inline unsigned int refcount_read(const refcount_t *r)
return atomic_read(&r->refs);
extern __must_check bool refcount_add_not_zero(unsigned int i, refcount_t *r);
extern void refcount_add(unsigned int i, refcount_t *r);
......@@ -52,6 +53,47 @@ extern void refcount_sub(unsigned int i, refcount_t *r);
extern __must_check bool refcount_dec_and_test(refcount_t *r);
extern void refcount_dec(refcount_t *r);
static inline __must_check bool refcount_add_not_zero(unsigned int i, refcount_t *r)
return atomic_add_unless(&r->refs, i, 0);
static inline void refcount_add(unsigned int i, refcount_t *r)
atomic_add(i, &r->refs);
static inline __must_check bool refcount_inc_not_zero(refcount_t *r)
return atomic_add_unless(&r->refs, 1, 0);
static inline void refcount_inc(refcount_t *r)
static inline __must_check bool refcount_sub_and_test(unsigned int i, refcount_t *r)
return atomic_sub_and_test(i, &r->refs);
static inline void refcount_sub(unsigned int i, refcount_t *r)
atomic_sub(i, &r->refs);
static inline __must_check bool refcount_dec_and_test(refcount_t *r)
return atomic_dec_and_test(&r->refs);
static inline void refcount_dec(refcount_t *r)
extern __must_check bool refcount_dec_if_one(refcount_t *r);
extern __must_check bool refcount_dec_not_one(refcount_t *r);
......@@ -37,6 +37,8 @@
#include <linux/refcount.h>
#include <linux/bug.h>
* refcount_add_not_zero - add a value to a refcount unless it is 0
* @i: the value to add to the refcount
......@@ -225,6 +227,7 @@ void refcount_dec(refcount_t *r)
WARN_ONCE(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
* refcount_dec_if_one - decrement a refcount if it is 1
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