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    Subject[PATCH 4.14 161/193] parisc: Fix validity check of pointer size argument in new CAS implementation
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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

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