linux-kernel - Re: [PATCH v2 23/44] metag: Traps

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Message-ID: <20121205174035.GX4939@ZenIV.linux.org.uk>
Date:	Wed, 5 Dec 2012 17:40:35 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	James Hogan <james.hogan@...tec.com>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2 23/44] metag: Traps

On Wed, Dec 05, 2012 at 04:08:41PM +0000, James Hogan wrote:
> +TBIRES tail_end(TBIRES State, unsigned long orig_syscall)
> +{
> +	struct pt_regs *regs = (struct pt_regs *)State.Sig.pCtx;
> +	unsigned long flags;
> +
> +	if (user_mode(regs)) {
> +		local_irq_enable();
> +		/* This is actually a crucial little line - if the process
> +		 * needs swapping out, then this is where it happens!
> +		 */
> +		if (need_resched())
> +			schedule();
> +
> +		flags = current_thread_info()->flags;
> +		if (flags & (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME)) {
> +			/* Note the passing in of the original syscall number.
> +			 * This is used for implementing signal restart.
> +			 */
> +			do_notify_resume(regs, orig_syscall != 0,
> +					 orig_syscall, flags);

Owww....  So
	a) you can't get there with !user_mode(regs)
	b) you handle only one signal (what happens if you fail sigframe
allocation, BTW?  Sure, you get SIGSEGV delivered.  And don't handle it.)
	c) you read ->flags with no protection whatsoever.  It should be
done *before* you enable interrupts, and rechecked after you've done
do_notify_resume() and redisabled them.  The same for schedule().  It really
should be a loop; take a look at how it's done on arm and alpha - there that
loop is in C, not in asm glue.
	d) looks like your sigreturn is, indeed, broken.  It should *not* have
syscall restart logics triggered at all.
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