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Subject[PATCH 4.9 078/138] parisc: Fix validity check of pointer size argument in new CAS implementation
4.9-stable review patch.  If anyone has any objections, please let me know.


From: John David Anglin <>

commit 05f016d2ca7a4fab99d5d5472168506ddf95e74f upstream.

As noted by Christoph Biedl, passing a pointer size of 4 in the new CAS
implementation causes a kernel crash. The attached patch corrects the
off by one error in the argument validity check.

In reviewing the code, I noticed that we only perform word operations
with the pointer size argument. The subi instruction intentionally uses
a word condition on 64-bit kernels. Nullification was used instead of a
cmpib instruction as the branch should never be taken. The shlw
pseudo-operation generates a depw,z instruction and it clears the target
before doing a shift left word deposit. Thus, we don't need to clip the
upper 32 bits of this argument on 64-bit kernels.

Tested with a gcc testsuite run with a 64-bit kernel. The gcc atomic
code in libgcc is the only direct user of the new CAS implementation
that I am aware of.

Signed-off-by: John David Anglin <>
Signed-off-by: Helge Deller <>
Signed-off-by: Greg Kroah-Hartman <>

arch/parisc/kernel/syscall.S | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/arch/parisc/kernel/syscall.S
+++ b/arch/parisc/kernel/syscall.S
@@ -690,15 +690,15 @@ cas_action:
/* ELF32 Process entry path */
#ifdef CONFIG_64BIT
- /* Clip the input registers */
+ /* Clip the input registers. We don't need to clip %r23 as we
+ only use it for word operations */
depdi 0, 31, 32, %r26
depdi 0, 31, 32, %r25
depdi 0, 31, 32, %r24
- depdi 0, 31, 32, %r23

/* Check the validity of the size pointer */
- subi,>>= 4, %r23, %r0
+ subi,>>= 3, %r23, %r0
b,n lws_exit_nosys

/* Jump to the functions which will load the old and new values into

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