Patch "parisc: Fix validity check of pointer size argument in new CAS implementation" has been added to the 4.9-stable tree

Patch "parisc: Fix validity check of pointer size argument in new CAS implementation" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    parisc: Fix validity check of pointer size argument in new CAS implementation

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     parisc-fix-validity-check-of-pointer-size-argument-in-new-cas-implementation.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 05f016d2ca7a4fab99d5d5472168506ddf95e74f Mon Sep 17 00:00:00 2001
From: John David Anglin <dave.anglin@bell.net>
Date: Sat, 11 Nov 2017 17:11:16 -0500
Subject: parisc: Fix validity check of pointer size argument in new CAS implementation

From: John David Anglin <dave.anglin@bell.net>

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 <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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 */
 lws_compare_and_swap_2:
 #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
 #endif
 
 	/* 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


Patches currently in stable-queue which might be from dave.anglin@bell.net are

queue-4.9/parisc-fix-validity-check-of-pointer-size-argument-in-new-cas-implementation.patch