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

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Date:	Thu, 23 Feb 2012 16:36:21 -0600
From:	Will Drewry <wad@...omium.org>
To:	Markus Gutschke <markus@...omium.org>
Cc:	Indan Zupancic <indan@....nu>,
	Roland McGrath <mcgrathr@...gle.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	Andrew Lutomirski <luto@....edu>, 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
Subject: Re: [PATCH v10 07/11] signal, x86: add SIGSYS info and make it synchronous.

On Thu, Feb 23, 2012 at 4:33 PM, Markus Gutschke <markus@...omium.org> wrote:
> On Thu, Feb 23, 2012 at 14:15, Indan Zupancic <indan@....nu> wrote:
>> What about making SECCOMP_RET_TRAP dump core/send SIGSYS if there is
>> no tracer with PTRACE_O_SECCOMP set?
>
> Please don't make things dependent on having a tracer. There are
> applications that don't really need a tracer; in fact, these are
> typically the exact same applications that can benefit from receiving
> SIGSYS and then handling it internally.
>
> If a tracer was required to set this up, it would make it difficult to
> use gdb, strace, or any other common debugging tools.
>
>> Sending SIGSYS is useful, but it's quite a bit less useful if user
>> space can't handle it in a signal handler, so I don't think it's
>> worth it to make a unblockable version.
>
> Maybe, I am not parsing your e-mail correctly. But don't we already
> get the desired behavior, if SIGSYS is treated the same as any other
> synchronous signal? If it is unblocked and has a handler, the
> application can decide to handle it. If neither one of these
> conditions is true, it terminates the program. Ulimits and
> PR_SET_DUMPABLE determine whether a core file is generated.

Yeah - the current patchset does that just fine. The tweak I was
proposing was making ti possible to deliver an SIGSYS that always uses
SIG_DFL so that you don't have to play with signal call enforcement in
the filters.

This is a pretty minor tweak either way.
cheers!
will
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