| Message ID | 1496180392-98718-2-git-send-email-keescook@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
> > 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 <keescook@chromium.org> > --- > arch/Kconfig | 9 +++++++++ > include/linux/refcount.h | 44 ++++++++++++++++++++++++++++++++++++++++++++ > lib/refcount.c | 3 +++ > 3 files changed, 56 insertions(+) > > diff --git a/arch/Kconfig b/arch/Kconfig > index 6c00e5b00f8b..fba3bf186728 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 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 b34aa649d204..68ecb431dbab 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 +53,49 @@ 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_return(i, &r->refs) != 0; > +} Maybe atomic_add_unless(&r->refs, i, 0) in order to be consistent with the below inc_not_zero implementation? > + > +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_return(i, &r->refs) == 0; > +} Any reason for not using atomic_sub_and_test() here? > + > +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_return(&r->refs) == 0; > +} Same here: atomic_dec_and_test()? Best Regards, Elena. > + > +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 9f906783987e..5d0582a9480c 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 > -- > 2.7.4
On Wed, May 31, 2017 at 10:45:09AM +0000, Reshetova, Elena wrote: > > +static inline __must_check bool refcount_add_not_zero(unsigned int i, > > + > > refcount_t *r) > > +{ > > + return atomic_add_return(i, &r->refs) != 0; > > +} > > Maybe atomic_add_unless(&r->refs, i, 0) in order to be consistent with the below inc_not_zero implementation? Yes, atomic_add_return() is strictly incorrect here since the add is unconditional. > > +static inline __must_check bool refcount_sub_and_test(unsigned int i, > > + > > refcount_t *r) > > +{ > > + return atomic_sub_return(i, &r->refs) == 0; > > +} > > Any reason for not using atomic_sub_and_test() here? > > +static inline __must_check bool refcount_dec_and_test(refcount_t *r) > > +{ > > + return atomic_dec_return(&r->refs) == 0; > > +} > > Same here: atomic_dec_and_test()? Both those are better because they return condition codes generated from the operand itself.
On Wed, May 31, 2017 at 4:09 AM, Peter Zijlstra <peterz@infradead.org> wrote: > On Wed, May 31, 2017 at 10:45:09AM +0000, Reshetova, Elena wrote: > >> > +static inline __must_check bool refcount_add_not_zero(unsigned int i, >> > + >> > refcount_t *r) >> > +{ >> > + return atomic_add_return(i, &r->refs) != 0; >> > +} >> >> Maybe atomic_add_unless(&r->refs, i, 0) in order to be consistent with the below inc_not_zero implementation? > > Yes, atomic_add_return() is strictly incorrect here since the add is > unconditional. > >> > +static inline __must_check bool refcount_sub_and_test(unsigned int i, >> > + >> > refcount_t *r) >> > +{ >> > + return atomic_sub_return(i, &r->refs) == 0; >> > +} >> >> Any reason for not using atomic_sub_and_test() here? > >> > +static inline __must_check bool refcount_dec_and_test(refcount_t *r) >> > +{ >> > + return atomic_dec_return(&r->refs) == 0; >> > +} >> >> Same here: atomic_dec_and_test()? > > Both those are better because they return condition codes generated from > the operand itself. Ah yes, thanks to both of you for the corrections. I'll send a new version... -Kees
diff --git a/arch/Kconfig b/arch/Kconfig index 6c00e5b00f8b..fba3bf186728 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 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 b34aa649d204..68ecb431dbab 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 +53,49 @@ 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_return(i, &r->refs) != 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_return(i, &r->refs) == 0; +} + +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_return(&r->refs) == 0; +} + +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 9f906783987e..5d0582a9480c 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
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 <keescook@chromium.org> --- arch/Kconfig | 9 +++++++++ include/linux/refcount.h | 44 ++++++++++++++++++++++++++++++++++++++++++++ lib/refcount.c | 3 +++ 3 files changed, 56 insertions(+)