kernel-hardening - Re: [PATCH v10 07/11] signal, x86: add SIGSYS info and make it synchronous.

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Message-ID: <4F459109.1060205@zytor.com>
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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