[PATCH 5.10 13/21] parisc/entry: fix trace test in syscall exit path

Greg Kroah-Hartman
2021-11-19T17:38:22Z

From: Sven Schnelle <svens@stackframe.org>

commit 3ec18fc7831e7d79e2d536dd1f3bc0d3ba425e8a upstream.

commit 8779e05ba8aa ("parisc: Fix ptrace check on syscall return")
fixed testing of TI_FLAGS. This uncovered a bug in the test mask.
syscall_restore_rfi is only used when the kernel needs to exit to
usespace with single or block stepping and the recovery counter
enabled. The test however used _TIF_SYSCALL_TRACE_MASK, which
includes a lot of bits that shouldn't be tested here.

Fix this by using TIF_SINGLESTEP and TIF_BLOCKSTEP directly.

I encountered this bug by enabling syscall tracepoints. Both in qemu and
on real hardware. As soon as i enabled the tracepoint (sys_exit_read,
but i guess it doesn't really matter which one), i got random page
faults in userspace almost immediately.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/parisc/kernel/entry.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/parisc/kernel/entry.S
+++ b/arch/parisc/kernel/entry.S
@@ -1849,7 +1849,7 @@ syscall_restore:

/* Are we being ptraced? */
LDREG TI_FLAGS-THREAD_SZ_ALGN-FRAME_SIZE(%r30),%r19
- ldi _TIF_SYSCALL_TRACE_MASK,%r2
+ ldi _TIF_SINGLESTEP|_TIF_BLOCKSTEP,%r2
and,COND(=) %r19,%r2,%r0
b,n syscall_restore_rfi