powerpc: Sanitize stack pointer in signal handling code

On powerpc64 machines running 32-bit userspace, we can get garbage bits in the
stack pointer passed into the kernel.  Most places handle this correctly, but
the signal handling code uses the passed value directly for allocating signal
stack frames.

This fixes the issue by introducing a get_clean_sp function that returns a
sanitized stack pointer.  For 32-bit tasks on a 64-bit kernel, the stack
pointer is masked correctly.  In all other cases, the stack pointer is simply
returned.

Additionally, we pass an 'is_32' parameter to get_sigframe now in order to
get the properly sanitized stack.  The callers are know to be 32 or 64-bit
statically.

Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index e132891d3cea..2fe6fc64b614 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -402,7 +402,7 @@ int handle_rt_signal64(int signr, struct k_sigaction *ka, siginfo_t *info,
         unsigned long newsp = 0;
         long err = 0;
 
-        frame = get_sigframe(ka, regs, sizeof(*frame));
+        frame = get_sigframe(ka, regs, sizeof(*frame), 0);
         if (unlikely(frame == NULL))
                 goto badframe;