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

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Message-ID: <CAE6n16kusCN9LxwqB1D2Dsm50mtc-6zkRje69D=QDdxxzWFTKw@mail.gmail.com>
Date:	Thu, 23 Feb 2012 14:33:02 -0800
From:	Markus Gutschke <markus@...omium.org>
To:	Indan Zupancic <indan@....nu>
Cc:	Will Drewry <wad@...omium.org>,
	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 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.

Markus
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