From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by sourceware.org (Postfix) with ESMTPS id 50F693857C46 for ; Wed, 4 Nov 2020 14:41:28 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 50F693857C46 Received: from gaia (unknown [2.26.170.190]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E5960206DB; Wed, 4 Nov 2020 14:41:23 +0000 (UTC) Date: Wed, 4 Nov 2020 14:41:21 +0000 From: Catalin Marinas To: Szabolcs Nagy Cc: Jeremy Linton , Mark Brown , libc-alpha@sourceware.org, Mark Rutland , Will Deacon , Florian Weimer , Kees Cook , Salvatore Mesoraca , Lennart Poettering , Topi Miettinen , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kernel-hardening@lists.openwall.com, linux-hardening@vger.kernel.org Subject: Re: [PATCH 0/4] aarch64: avoid mprotect(PROT_BTI|PROT_EXEC) [BZ #26831] Message-ID: <20201104144120.GD28902@gaia> References: <20201103173438.GD5545@sirena.org.uk> <8c99cc8e-41af-d066-b786-53ac13c2af8a@arm.com> <20201104085704.GB24704@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201104085704.GB24704@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS, KAM_DMARC_STATUS, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=no autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 04 Nov 2020 14:41:29 -0000 On Wed, Nov 04, 2020 at 08:57:05AM +0000, Szabolcs Nagy wrote: > The 11/03/2020 23:41, Jeremy Linton wrote: > > On 11/3/20 11:34 AM, Mark Brown wrote: > > > On Tue, Nov 03, 2020 at 10:25:37AM +0000, Szabolcs Nagy wrote: > > > > > > > Re-mmap executable segments instead of mprotecting them in > > > > case mprotect is seccomp filtered. > > > > > > > For the kernel mapped main executable we don't have the fd > > > > for re-mmap so linux needs to be updated to add BTI. (In the > > > > presence of seccomp filters for mprotect(PROT_EXEC) the libc > > > > cannot change BTI protection at runtime based on user space > > > > policy so it is better if the kernel maps BTI compatible > > > > binaries with PROT_BTI by default.) > > > > > > Given that there were still some ongoing discussions on a more robust > > > kernel interface here and there seem to be a few concerns with this > > > series should we perhaps just take a step back and disable this seccomp > > > filter in systemd on arm64, at least for the time being? That seems > > > safer than rolling out things that set ABI quickly, a big part of the > > > > So, that's a bigger hammer than I think is needed and punishes !BTI > > machines. I'm going to suggest that if we need to carry a temp patch its > > more like the glibc patch I mentioned in the Fedora defect. That patch > > simply logs a message, on the mprotect failures rather than aborting. Its > > fairly non-intrusive. > > > > That leaves seccomp functional, and BTI generally functional except when > > seccomp is restricting it. I've also been asked that if a patch like that is > > needed, its (temporary?) merged to the glibc trunk, rather than just being > > carried by the distro's. > > note that changing mprotect into mmap in glibc works > even if the kernel or systemd decides to do things > differently: currently the only wart is that on the > main exe we have to use mprotect and silently ignore > the failures. Can the dynamic loader mmap() the main exe again while munmap'ing the original one? (sorry if it was already discussed) -- Catalin