ARC: [Review] Prevent incorrect syscall restarts

Per Al Viro's "signals for dummies" https://lkml.org/lkml/2012/12/6/366
there are 3 golden rules for (not) restarting syscalls:

"	What we need to guarantee is
* restarts do not happen on signals caught in interrupts or exceptions
* restarts do not happen on signals caught in sigreturn()
* restart should happen only once, even if we get through do_signal()
  many times."

ARC Port already handled #1, this patch fixes #2 and #3.

We use the additional state in pt_regs->orig_r8 to ckh if restarting
has already been done once.

Thanks to Al Viro for spotting this.

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>

diff --git a/arch/arc/include/asm/ptrace.h b/arch/arc/include/asm/ptrace.h
index 3ec89f467ac3f4713909bbdcd0501086624d767f..a98957a95fb3d5e5cbb545efa9644c29d5b84ff4 100644 (file)
--- a/arch/arc/include/asm/ptrace.h
+++ b/arch/arc/include/asm/ptrace.h
@@ -100,6 +100,9 @@ struct callee_regs {
 #define in_syscall(regs)    (regs->event & orig_r8_IS_SCALL)
 #define in_brkpt_trap(regs) (regs->event & orig_r8_IS_BRKPT)
 
+#define syscall_wont_restart(regs) (regs->event |= orig_r8_IS_SCALL_RESTARTED)
+#define syscall_restartable(regs) !(regs->event &  orig_r8_IS_SCALL_RESTARTED)
+
 #define current_pt_regs()                                      \
 ({                                                             \
        /* open-coded current_thread_info() */                  \

diff --git a/arch/arc/kernel/signal.c b/arch/arc/kernel/signal.c
index ab8ed5a55461d8ea6ebe3a1ddd085c86500c4f45..ee6ef2f60a280c171e42c072401e9b7c1f79ae0c 100644 (file)
--- a/arch/arc/kernel/signal.c
+++ b/arch/arc/kernel/signal.c
@@ -128,6 +128,9 @@ SYSCALL_DEFINE0(rt_sigreturn)
                if (restore_altstack(&sf->uc.uc_stack))
                        goto badframe;
 
+       /* Don't restart from sigreturn */
+       syscall_wont_restart(regs);
+
        return regs->r0;
 
 badframe:
@@ -318,13 +321,13 @@ void do_signal(struct pt_regs *regs)
 
        signr = get_signal_to_deliver(&info, &ka, regs, NULL);
 
-       /* Are we from a system call? */
-       restart_scall = in_syscall(regs);
+       restart_scall = in_syscall(regs) && syscall_restartable(regs);
 
        if (signr > 0) {
-               if (restart_scall)
+               if (restart_scall) {
                        arc_restart_syscall(&ka, regs);
-
+                       syscall_wont_restart(regs);     /* No more restarts */
+               }
                handle_signal(signr, &ka, &info, regs);
                return;
        }
@@ -339,6 +342,7 @@ void do_signal(struct pt_regs *regs)
                        regs->r8 = __NR_restart_syscall;
                        regs->ret -= 4;
                }
+               syscall_wont_restart(regs);     /* No more restarts */
        }
 
        /* If there's no signal to deliver, restore the saved sigmask back */