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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>
This commit is contained in:
John David Anglin 2021-12-21 13:21:22 -05:00 committed by Helge Deller
parent 484730e586
commit 8f66fce0f4
1 changed files with 1 additions and 1 deletions
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arch/parisc/kernel/syscall.S
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@ -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