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futex: Sanitize cmpxchg_futex_value_locked API

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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: Michel Lespinasse <walken@google.com>
Acked-by: Chris Metcalf <cmetcalf@tilera.com>  [tile]
Acked-by: Tony Luck <tony.luck@intel.com>  [ia64]
Acked-by: Thomas 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: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Michel Lespinasse
2011-03-10 18:48:51 -08:00
committed by Thomas Gleixner
parent 522d7decc0
commit 37a9d912b2
20 changed files with 144 additions and 132 deletions
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18
arch/arm/include/asm/futex.h
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@@ -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 */