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Date:	Wed, 22 Feb 2012 17:06:17 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Roland McGrath <mcgrathr@...gle.com>
CC:	Kees Cook <keescook@...omium.org>, Will Drewry <wad@...omium.org>,
	Andrew Lutomirski <luto@....edu>,
	Indan Zupancic <indan@....nu>, 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,
	mingo@...hat.com, oleg@...hat.com, peterz@...radead.org,
	rdunlap@...otime.net, tglx@...utronix.de, eparis@...hat.com,
	serge.hallyn@...onical.com, djm@...drot.org, scarybeasts@...il.com,
	pmoore@...hat.com, akpm@...ux-foundation.org, corbet@....net,
	eric.dumazet@...il.com, markus@...omium.org
Subject: Re: [PATCH v10 07/11] signal, x86: add SIGSYS info and make it synchronous.

On 02/22/2012 04:50 PM, Roland McGrath wrote:
> On Wed, Feb 22, 2012 at 4:29 PM, H. Peter Anvin <hpa@...or.com> wrote:
>> Can we really introduce force-kill semantics for a POSIX-defined signal?
>> Other user space programs might use it for other purposes.
> 
> The semantics are based on how the signal was generated, not what signal
> number it was.  The only thing that depends on the signal number is
> SYNCHRONOUS_MASK, which just determines in which order pending signals are
> dequeued (POSIX says it may be any order).  We only have that so your state
> doesn't get unhelpfully warped to another signal handler entry point
> (including fiddling the stack) before you dump core.
> 
> No use of SIGSYS is specified by POSIX at all, of course, since "system
> call" is an implementation concept below the level POSIX specifies.

I meant whether or not a signal can be blocked/caught and the fact that
the signal exists at all.

Now I guess we could have "blockable" and "unblockable" SIGSYS, but that
would seem to have its own set of issues...

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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