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Subject[PATCH 2/2] ARC: [Review] Prevent incorrect syscall restarts
Date
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>
---
arch/arc/include/asm/ptrace.h | 3 +++
arch/arc/kernel/signal.c | 12 ++++++++----
2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/arc/include/asm/ptrace.h b/arch/arc/include/asm/ptrace.h
index 7daa3a6..caf216e 100644
--- a/arch/arc/include/asm/ptrace.h
+++ b/arch/arc/include/asm/ptrace.h
@@ -93,6 +93,9 @@ struct user_regs_struct {
#define in_syscall(regs) (regs->orig_r8 & orig_r8_IS_SCALL)
#define in_brkpt_trap(regs) (regs->orig_r8 & orig_r8_IS_BRKPT)

+#define syscall_wont_restart(regs) (regs->orig_r8 |= orig_r8_IS_SCALL_RESTARTED)
+#define syscall_restartable(regs) !(regs->orig_r8 & 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 464af3f..6671968 100644
--- a/arch/arc/kernel/signal.c
+++ b/arch/arc/kernel/signal.c
@@ -137,6 +137,9 @@ SYSCALL_DEFINE0(rt_sigreturn)
if (do_sigaltstack(&sf->uc.uc_stack, NULL, regs->sp) == -EFAULT)
goto badframe;

+ /* Don't restart from sigreturn */
+ syscall_wont_restart(regs);
+
return regs->r0;

badframe:
@@ -331,13 +334,13 @@ 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;
}
@@ -352,6 +355,7 @@ 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 */
--
1.7.4.1


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