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

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Message-ID: <CABqD9hbOi7Hk8X3zwewmvU1QTLQ_XDM140oS37XaZNtQajbDsQ@mail.gmail.com>
Date:	Tue, 28 Feb 2012 11:06:54 -0600
From:	Will Drewry <wad@...omium.org>
To:	Oleg Nesterov <oleg@...hat.com>
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 Tue, Feb 28, 2012 at 10:02 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> 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".

Err I meant "gets to go first".

> 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.

I believe it is.  I just want ucontext_t to be properly populate since
the registers were just rolled back for it.

>> > 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.

Sorry for the confusion

>> 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...

I guess I was thinking about users of signalfd wanting the call site
but force_ avoids it being blockable so that seems largely irrelevant
at present.

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

Thanks! I will try to clarify the changelog.
will
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