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    Subject[PATCH 4.19 26/38] parisc: Correct completer in lws start
    Date
    From: John David Anglin <dave.anglin@bell.net>

    commit 8f66fce0f46560b9e910787ff7ad0974441c4f9c upstream.

    The completer in the "or,ev %r1,%r30,%r30" instruction is reversed, so we are
    not clipping the LWS number when we are called from a 32-bit process (W=0).
    We need to nulify the following depdi instruction when the least-significant
    bit of %r30 is 1.

    If the %r20 register is not clipped, a user process could perform a LWS call
    that would branch to an undefined location in the kernel and potentially crash
    the machine.

    Signed-off-by: John David Anglin <dave.anglin@bell.net>
    Cc: stable@vger.kernel.org # 4.19+
    Signed-off-by: Helge Deller <deller@gmx.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/parisc/kernel/syscall.S | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/parisc/kernel/syscall.S
    +++ b/arch/parisc/kernel/syscall.S
    @@ -478,7 +478,7 @@ lws_start:
    extrd,u %r1,PSW_W_BIT,1,%r1
    /* sp must be aligned on 4, so deposit the W bit setting into
    * the bottom of sp temporarily */
    - or,ev %r1,%r30,%r30
    + or,od %r1,%r30,%r30

    /* Clip LWS number to a 32-bit value for 32-bit processes */
    depdi 0, 31, 32, %r20

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