Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753249Ab2BVXxO (ORCPT ); Wed, 22 Feb 2012 18:53:14 -0500 Received: from mail-tul01m020-f174.google.com ([209.85.214.174]:59321 "EHLO mail-tul01m020-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753018Ab2BVXxL convert rfc822-to-8bit (ORCPT ); Wed, 22 Feb 2012 18:53:11 -0500 Authentication-Results: mr.google.com; spf=pass (google.com: domain of keescook@google.com designates 10.182.147.106 as permitted sender) smtp.mail=keescook@google.com; dkim=pass header.i=keescook@google.com 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 15:53:08 -0800 X-Google-Sender-Auth: YAXl-SVcUcsEsdCMKv5MzQI9x_Y Message-ID: Subject: Re: [PATCH v10 07/11] signal, x86: add SIGSYS info and make it synchronous. From: Kees Cook To: Andrew Lutomirski Cc: Will Drewry , 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 X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2750 Lines: 59 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. -Kees -- Kees Cook ChromeOS Security -- 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/