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 <keescook@chromium.org>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: David Windsor <dwindsor@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Elena Reshetova <elena.reshetova@intel.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Hans Liljestrand <ishkamiel@gmail.com>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>
Cc: Jann Horn <jannh@google.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Serge E. Hallyn <serge@hallyn.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: arozansk@redhat.com
Cc: axboe@kernel.dk
Cc: linux-arch <linux-arch@vger.kernel.org>
Link: http://lkml.kernel.org/r/20170621200026.GA115679@beast


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent f9e16988

arch/Kconfig

+9 −0
Original line number Diff line number Diff line
@@ -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"

include/linux/refcount.h

+42 −0
Original line number Diff line number Diff line
@@ -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);

lib/refcount.c

+3 −0
Original line number Diff line number Diff line
@@ -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

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