Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753468Ab2BWAFL (ORCPT ); Wed, 22 Feb 2012 19:05:11 -0500 Received: from mail-lpp01m010-f46.google.com ([209.85.215.46]:58661 "EHLO mail-lpp01m010-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752930Ab2BWAFI convert rfc822-to-8bit (ORCPT ); Wed, 22 Feb 2012 19:05:08 -0500 MIME-Version: 1.0 In-Reply-To: References: <1329845435-2313-1-git-send-email-wad@chromium.org> <1329845435-2313-7-git-send-email-wad@chromium.org> <9edbabb2262e3d91a7b8c75dbec03d7f.squirrel@webmail.greenhost.nl> Date: Wed, 22 Feb 2012 18:05:05 -0600 Message-ID: Subject: Re: [PATCH v10 07/11] signal, x86: add SIGSYS info and make it synchronous. From: Will Drewry To: Kees Cook Cc: Andrew Lutomirski , Indan Zupancic , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, kernel-hardening@lists.openwall.com, netdev@vger.kernel.org, x86@kernel.org, arnd@arndb.de, davem@davemloft.net, hpa@zytor.com, mingo@redhat.com, oleg@redhat.com, peterz@infradead.org, rdunlap@xenotime.net, mcgrathr@chromium.org, tglx@linutronix.de, eparis@redhat.com, serge.hallyn@canonical.com, djm@mindrot.org, scarybeasts@gmail.com, pmoore@redhat.com, akpm@linux-foundation.org, corbet@lwn.net, eric.dumazet@gmail.com, markus@chromium.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3023 Lines: 58 On Wed, Feb 22, 2012 at 5:53 PM, Kees Cook wrote: > On Wed, Feb 22, 2012 at 3:38 PM, Andrew Lutomirski wrote: >> On Wed, Feb 22, 2012 at 11:48 AM, Will Drewry wrote: >>> On Wed, Feb 22, 2012 at 2:34 AM, Indan Zupancic wrote: >>>> On Tue, February 21, 2012 18:30, Will Drewry wrote: >>>>> This change enables SIGSYS, defines _sigfields._sigsys, and adds >>>>> x86 (compat) arch support. ?_sigsys defines fields which allow >>>>> a signal handler to receive the triggering system call number, >>>>> the relevant AUDIT_ARCH_* value for that number, and the address >>>>> of the callsite. >>>>> >>>>> To ensure that SIGSYS delivery occurs on return from the triggering >>>>> system call, SIGSYS is added to the SYNCHRONOUS_MASK macro. ?I'm >>>>> this is enough to ensure it will be synchronous or if it is explicitly >>>>> required to ensure an immediate delivery of the signal upon return from >>>>> the blocked system call. >>>>> >>>>> The first consumer of SIGSYS would be seccomp filter. ?In particular, >>>>> a filter program could specify a new return value, SECCOMP_RET_TRAP, >>>>> which would result in the system call being denied and the calling >>>>> thread signaled. ?This also means that implementing arch-specific >>>>> support can be dependent upon HAVE_ARCH_SECCOMP_FILTER. >>>> >>>> I think others said this is useful, but I don't see how. Easier >>>> debugging compared to checking return values? >>>> >>>> I suppose SIGSYS can be blocked, so there is no guarantee the process >>>> will be killed. >>> >>> Yeah, this allows for in-process system call emulation, if desired, or >>> for the process to dump core/etc. ?With RET_ERRNO or RET_KILL, there >>> isn't any feedback to the system about the state of the process. ?Kill >>> populates audit_seccomp and dmesg, but if the application >>> user/developer isn't the system admin, installing audit bits or >>> checking system logs seems onerous. >> >> [Warning: this suggestion may be bad for any number of reasons] >> >> I wonder if it would be helpful to change the semantics of RET_KILL >> slightly. ?Rather than killing via do_exit, what if it killed via a >> forcibly-fatal SIGSYS? ?That way, the parent's waitid() / SIGCHLD >> would indicate CLD_KILLED with si_status == SIGSYS. ?The parent could >> check that and report that the child was probably compromised. >> >> --Andy > > I'd prefer sticking with do_exit. This provides much less chance of > things going wrong. A parent seeing a child killed with SIGKILL is > already pretty distinct, IMO. Hrm, it might be possible to do_exit(SIGSYS) which would be both. It looks like tsk->exit_code would be SIGSYS then, but I'll look a little more closely to see what that'll actually do. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/