From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from second.openwall.net (second.openwall.net [193.110.157.125]) by smtp.lore.kernel.org (Postfix) with SMTP id A0398C3DA49 for ; Thu, 18 Jul 2024 12:23:43 +0000 (UTC) Received: (qmail 23597 invoked by uid 550); 18 Jul 2024 12:23:31 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 23571 invoked from network); 18 Jul 2024 12:23:31 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=digikod.net; s=20191114; t=1721305402; bh=2miiI/5j4wTJs9zVbOsNd+rOxv6jp8fs/L7lmo5Xt3s=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=gy83JArLMq864jKTREMY1Kn2Kfo3QT5j03SQkLmXwJryYVvObFoTAR0tvHMpGFGPN URCOIjHWu2cVo1uWWxNDPbO0VqEVGtxcbbezzRaNyXizzRIpp/q6ln8nyKGU/scq+u fBbAw+t6lcv38UVvqf0UWNtLJfRnqBjQr2qzl5lM= Date: Thu, 18 Jul 2024 14:23:19 +0200 From: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= To: Jeff Xu Cc: Steve Dower , Al Viro , Christian Brauner , Kees Cook , Linus Torvalds , Paul Moore , Theodore Ts'o , Alejandro Colomar , Aleksa Sarai , Andrew Morton , Andy Lutomirski , Arnd Bergmann , Casey Schaufler , Christian Heimes , Dmitry Vyukov , Eric Biggers , Eric Chiang , Fan Wu , Florian Weimer , Geert Uytterhoeven , James Morris , Jan Kara , Jann Horn , Jonathan Corbet , Jordan R Abrahams , Lakshmi Ramasubramanian , Luca Boccassi , Luis Chamberlain , "Madhavan T . Venkataraman" , Matt Bobrowski , Matthew Garrett , Matthew Wilcox , Miklos Szeredi , Mimi Zohar , Nicolas Bouchinet , Scott Shell , Shuah Khan , Stephen Rothwell , Steve Grubb , Thibaut Sautereau , Vincent Strubel , Xiaoming Ni , Yin Fengwei , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Elliott Hughes Subject: Re: [RFC PATCH v19 1/5] exec: Add a new AT_CHECK flag to execveat(2) Message-ID: <20240718.ahph4che5Shi@digikod.net> References: <20240704190137.696169-1-mic@digikod.net> <20240704190137.696169-2-mic@digikod.net> <20240717.AGh2shahc9ee@digikod.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Infomaniak-Routing: alpha On Wed, Jul 17, 2024 at 06:51:11PM -0700, Jeff Xu wrote: > On Wed, Jul 17, 2024 at 3:00 AM Mickaël Salaün wrote: > > > > On Wed, Jul 17, 2024 at 09:26:22AM +0100, Steve Dower wrote: > > > On 17/07/2024 07:33, Jeff Xu wrote: > > > > Consider those cases: I think: > > > > a> relying purely on userspace for enforcement does't seem to be > > > > effective, e.g. it is trivial to call open(), then mmap() it into > > > > executable memory. > > > > > > If there's a way to do this without running executable code that had to pass > > > a previous execveat() check, then yeah, it's not effective (e.g. a Python > > > interpreter that *doesn't* enforce execveat() is a trivial way to do it). > > > > > > Once arbitrary code is running, all bets are off. So long as all arbitrary > > > code is being checked itself, it's allowed to do things that would bypass > > > later checks (and it's up to whoever audited it in the first place to > > > prevent this by not giving it the special mark that allows it to pass the > > > check). > > > We will want to define what is considered as "arbitrary code is running" > > Using an example of ROP, attackers change the return address in stack, > e.g. direct the execution flow to a gauge to call "ld.so /tmp/a.out", > do you consider "arbitrary code is running" when stack is overwritten > ? or after execve() is called. Yes, ROP is arbitrary code execution (which can be mitigated with CFI). ROP could be enough to interpret custom commands and create a small interpreter/VM. > If it is later, this patch can prevent "ld.so /tmp/a.out". > > > Exactly. As explained in the patches, one crucial prerequisite is that > > the executable code is trusted, and the system must provide integrity > > guarantees. We cannot do anything without that. This patches series is > > a building block to fix a blind spot on Linux systems to be able to > > fully control executability. > > Even trusted executable can have a bug. Definitely, but this patch series is dedicated to script execution control. > > I'm thinking in the context of ChromeOS, where all its system services > are from trusted partitions, and legit code won't load .so from a > non-exec mount. But we want to sandbox those services, so even under > some kind of ROP attack, the service still won't be able to load .so > from /tmp. Of course, if an attacker can already write arbitrary > length of data into the stack, it is probably already a game over. > OK, you want to tie executable file permission to mmap. That makes sense if you have a consistent execution model. This can be enforced by LSMs. Contrary to script interpretation which is a full user space implementation (and then controlled by user space), mmap restrictions should indeed be enforced by the kernel.