parisc: Correct completer in lws start

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>

diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S
index d2497b3..65c88ca 100644 (file)
--- a/arch/parisc/kernel/syscall.S
+++ b/arch/parisc/kernel/syscall.S
@@ -472,7 +472,7 @@ 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