Commit 55bb9480 authored by Vineet Gupta's avatar Vineet Gupta
Browse files

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: default avatarVineet Gupta <vgupta@synopsys.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
parent 5c39c0ab

arch/arc/include/asm/ptrace.h

+3 −0
Original line number Diff line number Diff line
@@ -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() */			\

arch/arc/kernel/signal.c

+8 −4
Original line number Diff line number Diff line
@@ -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 */

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