linux-kernel - Re: [PATCH v11 08/12] signal, x86: add SIGSYS info and make it synchronous.

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Date:	Tue, 28 Feb 2012 17:02:57 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Will Drewry <wad@...omium.org>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-doc@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	netdev@...r.kernel.org, x86@...nel.org, arnd@...db.de,
	davem@...emloft.net, hpa@...or.com, mingo@...hat.com,
	peterz@...radead.org, rdunlap@...otime.net, mcgrathr@...omium.org,
	tglx@...utronix.de, luto@....edu, eparis@...hat.com,
	serge.hallyn@...onical.com, djm@...drot.org, scarybeasts@...il.com,
	indan@....nu, pmoore@...hat.com, akpm@...ux-foundation.org,
	corbet@....net, eric.dumazet@...il.com, markus@...omium.org,
	coreyb@...ux.vnet.ibm.com, keescook@...omium.org
Subject: Re: [PATCH v11 08/12] signal, x86: add SIGSYS info and make it
	synchronous.

On 02/27, Will Drewry wrote:
>
> On Mon, Feb 27, 2012 at 11:22 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> > On 02/24, Will Drewry wrote:
> >>
> >> To ensure that SIGSYS delivery occurs on return from the triggering
> >> system call, SIGSYS is added to the SYNCHRONOUS_MASK macro.
> >
> > Hmm. Can't understand... please help.
> >
> >>  #define SYNCHRONOUS_MASK \
> >>       (sigmask(SIGSEGV) | sigmask(SIGBUS) | sigmask(SIGILL) | \
> >> -      sigmask(SIGTRAP) | sigmask(SIGFPE))
> >> +      sigmask(SIGTRAP) | sigmask(SIGFPE) | sigmask(SIGSYS))
> >
> > Why?
> >
> > SYNCHRONOUS_MASK just tells dequeue_signal() "pick them first".
> > This is needed to make sure that the handler for, say SIGSEGV,
> > can use ucontext->ip as a faulting addr.
>
> I think that Roland covered this.  (Since the syscall_rollback was
> called it's nice to let our handler get first go.)

OK, except I do not really understand the "our handler get first go".

Suppose SIGSYS "races" with the pending SIGHUP. With this change
the caller for SIGHUP will be called first. But yes, setup_frame()
will be called for SIGSYS first. Hopefully this is what you want.

> > But seccomp adds info->si_call_addr, this looks unneeded.
>
> True enough.  I can drop it.

Hmm. I meant, the change in SYNCHRONOUS_MASK looks unneeded. Please
keep ->si_call_addr, it is much more convenient than ucontext_t in
userspace.

> It'd only be useful if the SIGSYS wasn't
> being forced and the signal was being handled without ucontext_t
> access.

No, force_ doesn't make any difference in this sense...

In short, the patch looks fine to me, but if you resend it may be
you can update the changelog.

Oleg.

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