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

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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>
This commit is contained in:
John David Anglin 2017-11-11 17:11:16 -05:00 • committed by Greg Kroah-Hartman
parent aef7cdb6a6
commit 937a91cd39
1 changed files with 3 additions and 3 deletions
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6
arch/parisc/kernel/syscall.S
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@ -688,15 +688,15 @@ 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