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

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Message-ID: <CABqD9hbBj_c1qxD7N0ed3LMy_DXn-163LuNc1E7mSZbGO7oqyw@mail.gmail.com>
Date:	Mon, 27 Feb 2012 14:24:04 -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 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.)

> But seccomp adds info->si_call_addr, this looks unneeded.

True enough.  I can drop it.  It'd only be useful if the SIGSYS wasn't
being forced and the signal was being handled without ucontext_t
access.

thanks!
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