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 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

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-4.14 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-4.14/parisc-fix-validity-check-of-pointer-size-argument-in-new-cas-implementation.patch