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, 18 insertions, 19 deletions

diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c
index b3273aeaeedc..604f077bb5bf 100644
--- a/arch/mips/kernel/signal.c
+++ b/arch/mips/kernel/signal.c
@@ -550,23 +550,26 @@ static int handle_signal(unsigned long sig, siginfo_t *info,
         struct mips_abi *abi = current->thread.abi;
         void *vdso = current->mm->context.vdso;
 
-        switch(regs->regs[0]) {
-        case ERESTART_RESTARTBLOCK:
-        case ERESTARTNOHAND:
-                regs->regs[2] = EINTR;
-                break;
-        case ERESTARTSYS:
-                if (!(ka->sa.sa_flags & SA_RESTART)) {
+        if (regs->regs[0]) {
+                switch(regs->regs[2]) {
+                case ERESTART_RESTARTBLOCK:
+                case ERESTARTNOHAND:
                         regs->regs[2] = EINTR;
                         break;
+                case ERESTARTSYS:
+                        if (!(ka->sa.sa_flags & SA_RESTART)) {
+                                regs->regs[2] = EINTR;
+                                break;
+                        }
+                /* fallthrough */
+                case ERESTARTNOINTR:
+                        regs->regs[7] = regs->regs[26];
+                        regs->regs[2] = regs->regs[0];
+                        regs->cp0_epc -= 4;
                 }
-        /* fallthrough */
-        case ERESTARTNOINTR:            /* Userland will reload $v0.  */
-                regs->regs[7] = regs->regs[26];
-                regs->cp0_epc -= 8;
-        }
 
-        regs->regs[0] = 0;              /* Don't deal with this again.  */
+                regs->regs[0] = 0;              /* Don't deal with this again.  */
+        }
 
         if (sig_uses_siginfo(ka))
                 ret = abi->setup_rt_frame(vdso + abi->rt_signal_return_offset,
@@ -625,17 +628,13 @@ static void do_signal(struct pt_regs *regs)
                 return;
         }
 
-        /*
-         * Who's code doesn't conform to the restartable syscall convention
-         * dies here!!!  The li instruction, a single machine instruction,
-         * must directly be followed by the syscall instruction.
-         */
         if (regs->regs[0]) {
                 if (regs->regs[2] == ERESTARTNOHAND ||
                     regs->regs[2] == ERESTARTSYS ||
                     regs->regs[2] == ERESTARTNOINTR) {
+                        regs->regs[2] = regs->regs[0];
                         regs->regs[7] = regs->regs[26];
-                        regs->cp0_epc -= 8;
+                        regs->cp0_epc -= 4;
                 }
                 if (regs->regs[2] == ERESTART_RESTARTBLOCK) {
                         regs->regs[2] = current->thread.abi->restart;