Commit-ID: 87f7583e9205fe5220677d0775f3a4d2b8fe8827 Gitweb: http://git.kernel.org/tip/87f7583e9205fe5220677d0775f3a4d2b8fe8827 Author: Kees Cook <[email protected]> AuthorDate: Wed, 21 Jun 2017 13:00:26 -0700 Committer: Ingo Molnar <[email protected]> CommitDate: Thu, 22 Jun 2017 10:36:25 +0200
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: Kees Cook <[email protected]> Acked-by: Greg Kroah-Hartman <[email protected]> Cc: Alexey Dobriyan <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Arnd Bergmann <[email protected]> Cc: Christoph Hellwig <[email protected]> Cc: David S. Miller <[email protected]> Cc: David Windsor <[email protected]> Cc: Davidlohr Bueso <[email protected]> Cc: Elena Reshetova <[email protected]> Cc: Eric Biggers <[email protected]> Cc: Eric W. Biederman <[email protected]> Cc: Hans Liljestrand <[email protected]> Cc: James Bottomley <[email protected]> Cc: Jann Horn <[email protected]> Cc: Josh Poimboeuf <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Manfred Spraul <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Serge E. Hallyn <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: [email protected] Cc: [email protected] Cc: linux-arch <[email protected]> Link: http://lkml.kernel.org/r/20170621200026.GA115679@beast Signed-off-by: Ingo Molnar <[email protected]> --- arch/Kconfig | 9 +++++++++ include/linux/refcount.h | 42 ++++++++++++++++++++++++++++++++++++++++++ lib/refcount.c | 3 +++ 3 files changed, 54 insertions(+) diff --git a/arch/Kconfig b/arch/Kconfig index 6c00e5b..f76b214 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -867,4 +867,13 @@ config STRICT_MODULE_RWX config ARCH_WANT_RELAX_ORDER bool +config REFCOUNT_FULL + bool "Perform full reference count validation at the expense of speed" + help + 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" diff --git a/include/linux/refcount.h b/include/linux/refcount.h index b34aa64..bb71f28 100644 --- a/include/linux/refcount.h +++ b/include/linux/refcount.h @@ -41,6 +41,7 @@ static inline unsigned int refcount_read(const refcount_t *r) return atomic_read(&r->refs); } +#ifdef CONFIG_REFCOUNT_FULL 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); +#else +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) +{ + atomic_inc(&r->refs); +} + +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) +{ + atomic_dec(&r->refs); +} +#endif /* CONFIG_REFCOUNT_FULL */ extern __must_check bool refcount_dec_if_one(refcount_t *r); extern __must_check bool refcount_dec_not_one(refcount_t *r); diff --git a/lib/refcount.c b/lib/refcount.c index 9f90678..5d0582a 100644 --- a/lib/refcount.c +++ b/lib/refcount.c @@ -37,6 +37,8 @@ #include <linux/refcount.h> #include <linux/bug.h> +#ifdef CONFIG_REFCOUNT_FULL + /** * 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"); } EXPORT_SYMBOL(refcount_dec); +#endif /* CONFIG_REFCOUNT_FULL */ /** * refcount_dec_if_one - decrement a refcount if it is 1
