MIPS: Sanitize restart logics

Put the original syscall number into ->regs[0] when we leave syscall
with error.  Use it in restart logics.  Everything else will have
it 0 since we pass through SAVE_SOME on all the ways in.  Note that
in places like bad_stack and inllegal_syscall we leave it 0 - it's not
restartable.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-kernel@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1698/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/arch/mips/kernel/scall64-64.S b/arch/mips/kernel/scall64-64.S
index a8a6c596eb04..eb0bb73172c3 100644
--- a/arch/mips/kernel/scall64-64.S
+++ b/arch/mips/kernel/scall64-64.S
@@ -66,9 +66,9 @@ NESTED(handle_sys64, PT_SIZE, sp)
         sd      t0, PT_R7(sp)           # set error flag
         beqz    t0, 1f
 
+        ld      t1, PT_R2(sp)           # syscall number
         dnegu   v0                      # error
-        sd      v0, PT_R0(sp)           # set flag for syscall
-                                        # restarting
+        sd      t1, PT_R0(sp)           # save it for syscall restarting
 1:      sd      v0, PT_R2(sp)           # result
 
 n64_syscall_exit:
@@ -109,8 +109,9 @@ syscall_trace_entry:
         sd      t0, PT_R7(sp)           # set error flag
         beqz    t0, 1f
 
+        ld      t1, PT_R2(sp)           # syscall number
         dnegu   v0                      # error
-        sd      v0, PT_R0(sp)           # set flag for syscall restarting
+        sd      t1, PT_R0(sp)           # save it for syscall restarting
 1:      sd      v0, PT_R2(sp)           # result
 
         j       syscall_exit