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 3ec89f4..a98957a 100644
--- a/arch/arc/include/asm/ptrace.h
+++ b/arch/arc/include/asm/ptrace.h
@@ -100,6 +100,9 @@
#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 ab8ed5a..ee6ef2f 100644
--- a/arch/arc/kernel/signal.c
+++ b/arch/arc/kernel/signal.c
@@ -128,6 +128,9 @@
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 @@
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 @@
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 */