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ia64: fix futex_atomic_cmpxchg_inatomic()

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commit c76f39bddb upstream.

Michel Lespinasse cleaned up the futex calling conventions in commit
37a9d912b2 ("futex: Sanitize cmpxchg_futex_value_locked API").

But the ia64 implementation was subtly broken.  Gcc does not know that
register "r8" will be updated by the fault handler if the cmpxchg
instruction takes an exception.  So it feels safe in letting the
initialization of r8 slide to after the cmpxchg.  Result: we always
return 0 whether the user address faulted or not.

Fix by moving the initialization of r8 into the __asm__ code so gcc
won't move it.

Reported-by: <emeric.maschino@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=42757
Tested-by: <emeric.maschino@gmail.com>
Acked-by: Michel Lespinasse <walken@google.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Luck, Tony
2012-04-16 16:28:01 -07:00
committed by Greg Kroah-Hartman
parent 23066aae74
commit e04a331e00
1 changed files with 5 additions and 4 deletions
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9
arch/ia64/include/asm/futex.h
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@@ -107,15 +107,16 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
return -EFAULT;
{
register unsigned long r8 __asm ("r8") = 0;
register unsigned long r8 __asm ("r8");
unsigned long prev;
__asm__ __volatile__(
" mf;; \n"
" mov ar.ccv=%3;; \n"
"[1:] cmpxchg4.acq %0=[%1],%2,ar.ccv \n"
" mov %0=r0 \n"
" mov ar.ccv=%4;; \n"
"[1:] cmpxchg4.acq %1=[%2],%3,ar.ccv \n"
" .xdata4 \"__ex_table\", 1b-., 2f-. \n"
"[2:]"
: "=r" (prev)
: "=r" (r8), "=r" (prev)
: "r" (uaddr), "r" (newval),
"rO" ((long) (unsigned) oldval)
: "memory");