Commit 37a9d912 authored by Michel Lespinasse's avatar Michel Lespinasse Committed by Thomas Gleixner
Browse files

futex: Sanitize cmpxchg_futex_value_locked API 



The cmpxchg_futex_value_locked API was funny in that it returned either
the original, user-exposed futex value OR an error code such as -EFAULT.
This was confusing at best, and could be a source of livelocks in places
that retry the cmpxchg_futex_value_locked after trying to fix the issue
by running fault_in_user_writeable().
    
This change makes the cmpxchg_futex_value_locked API more similar to the
get_futex_value_locked one, returning an error code and updating the
original value through a reference argument.
    
Signed-off-by: default avatarMichel Lespinasse <walken@google.com>
Acked-by: Chris Metcalf <cmetcalf@tilera.com>  [tile]
Acked-by: Tony Luck <tony.luck@intel.com>  [ia64]
Acked-by: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: Michal Simek <monstr@monstr.eu>  [microblaze]
Acked-by: David Howells <dhowells@redhat.com> [frv]
Cc: Darren Hart <darren@dvhart.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20110311024851.GC26122@google.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 522d7dec

arch/alpha/include/asm/futex.h

+12 −10
Original line number Diff line number Diff line
@@ -81,21 +81,22 @@ static inline int futex_atomic_op_inuser (int encoded_op, int __user *uaddr) 
}



static inline int

futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)

futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,

			      int oldval, int newval)

{

	int prev, cmp;

	int ret = 0, prev, cmp;



	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))

		return -EFAULT;



	__asm__ __volatile__ (

		__ASM_SMP_MB

	"1:	ldl_l	%0,0(%2)\n"

	"	cmpeq	%0,%3,%1\n"

	"	beq	%1,3f\n"

	"	mov	%4,%1\n"

	"2:	stl_c	%1,0(%2)\n"

	"	beq	%1,4f\n"

	"1:	ldl_l	%1,0(%3)\n"

	"	cmpeq	%1,%4,%2\n"

	"	beq	%2,3f\n"

	"	mov	%5,%2\n"

	"2:	stl_c	%2,0(%3)\n"

	"	beq	%2,4f\n"

	"3:	.subsection 2\n"

	"4:	br	1b\n"

	"	.previous\n"
@@ -105,11 +106,12 @@ futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval) 
	"	.long	2b-.\n"

	"	lda	$31,3b-2b(%0)\n"

	"	.previous\n"

	:	"=&r"(prev), "=&r"(cmp)

	:	"+r"(ret), "=&r"(prev), "=&r"(cmp)

	:	"r"(uaddr), "r"((long)oldval), "r"(newval)

	:	"memory");



	return prev;

	*uval = prev;

	return ret;

}



#endif /* __KERNEL__ */

arch/arm/include/asm/futex.h

+10 −8
Original line number Diff line number Diff line
@@ -88,9 +88,10 @@ futex_atomic_op_inuser (int encoded_op, int __user *uaddr) 
}



static inline int

futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)

futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,

			      int oldval, int newval)

{

	int val;

	int ret = 0, val;



	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))

		return -EFAULT;
@@ -99,24 +100,25 @@ futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval) 
	 * call sites. */



	__asm__ __volatile__("@futex_atomic_cmpxchg_inatomic\n"

	"1:	" T(ldr) "	%0, [%3]\n"

	"	teq	%0, %1\n"

	"1:	" T(ldr) "	%1, [%4]\n"

	"	teq	%1, %2\n"

	"	it	eq	@ explicit IT needed for the 2b label\n"

	"2:	" T(streq) "	%2, [%3]\n"

	"2:	" T(streq) "	%3, [%4]\n"

	"3:\n"

	"	.pushsection __ex_table,\"a\"\n"

	"	.align	3\n"

	"	.long	1b, 4f, 2b, 4f\n"

	"	.popsection\n"

	"	.pushsection .fixup,\"ax\"\n"

	"4:	mov	%0, %4\n"

	"4:	mov	%0, %5\n"

	"	b	3b\n"

	"	.popsection"

	: "=&r" (val)

	: "+r" (ret), "=&r" (val)

	: "r" (oldval), "r" (newval), "r" (uaddr), "Ir" (-EFAULT)

	: "cc", "memory");



	return val;

	*uval = val;

	return ret;

}



#endif /* !SMP */

arch/frv/include/asm/futex.h

+2 −1
Original line number Diff line number Diff line
@@ -10,7 +10,8 @@ 
extern int futex_atomic_op_inuser(int encoded_op, int __user *uaddr);



static inline int

futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)

futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,

			      int oldval, int newval)

{

	return -ENOSYS;

}

arch/ia64/include/asm/futex.h

+6 −3
Original line number Diff line number Diff line
@@ -100,23 +100,26 @@ futex_atomic_op_inuser (int encoded_op, int __user *uaddr) 
}



static inline int

futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)

futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,

			      int oldval, int newval)

{

	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))

		return -EFAULT;



	{

		register unsigned long r8 __asm ("r8");

		register unsigned long r8 __asm ("r8") = 0;

		unsigned long prev;

		__asm__ __volatile__(

			"	mf;;					\n"

			"	mov ar.ccv=%3;;				\n"

			"[1:]	cmpxchg4.acq %0=[%1],%2,ar.ccv		\n"

			"	.xdata4 \"__ex_table\", 1b-., 2f-.	\n"

			"[2:]"

			: "=r" (r8)

			: "=r" (prev)

			: "r" (uaddr), "r" (newval),

			  "rO" ((long) (unsigned) oldval)

			: "memory");

		*uval = prev;

		return r8;

	}

}

arch/microblaze/include/asm/futex.h

+13 −11
Original line number Diff line number Diff line
@@ -94,31 +94,33 @@ futex_atomic_op_inuser(int encoded_op, int __user *uaddr) 
}



static inline int

futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)

futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,

			      int oldval, int newval)

{

	int prev, cmp;

	int ret = 0, prev, cmp;



	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))

		return -EFAULT;



	__asm__ __volatile__ ("1:	lwx	%0, %2, r0;		\

					cmp	%1, %0, %3;		\

					beqi	%1, 3f;			\

				2:	swx	%4, %2, r0;		\

					addic	%1, r0, 0;		\

					bnei	%1, 1b;			\

	__asm__ __volatile__ ("1:	lwx	%1, %3, r0;		\

					cmp	%2, %1, %4;		\

					beqi	%2, 3f;			\

				2:	swx	%5, %3, r0;		\

					addic	%2, r0, 0;		\

					bnei	%2, 1b;			\

				3:					\

				.section .fixup,\"ax\";			\

				4:	brid	3b;			\

					addik	%0, r0, %5;		\

					addik	%0, r0, %6;		\

				.previous;				\

				.section __ex_table,\"a\";		\

				.word	1b,4b,2b,4b;			\

				.previous;"				\

		: "=&r" (prev), "=&r"(cmp)				\

		: "+r" (ret), "=&r" (prev), "=&r"(cmp)	\

		: "r" (uaddr), "r" (oldval), "r" (newval), "i" (-EFAULT));



	return prev;

	*uval = prev;

	return ret;

}



#endif /* __KERNEL__ */

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