From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by sourceware.org (Postfix) with ESMTP id 53C7A38515E2 for ; Thu, 10 Jun 2021 17:02:13 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 53C7A38515E2 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 074851396; Thu, 10 Jun 2021 10:02:13 -0700 (PDT) Received: from [192.168.122.166] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9AD043F719; Thu, 10 Jun 2021 10:02:12 -0700 (PDT) Subject: Re: [PATCH v2 0/3] arm64: Enable BTI for the executable as well as the interpreter To: Mark Brown , Catalin Marinas , Will Deacon Cc: Szabolcs Nagy , Dave Martin , "H . J . Lu" , Yu-cheng Yu , linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, libc-alpha@sourceware.org References: <20210604112450.13344-1-broonie@kernel.org> From: Jeremy Linton Message-ID: <43e67d7b-aab9-db1f-f74b-a87ba7442d47@arm.com> Date: Thu, 10 Jun 2021 11:28:12 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210604112450.13344-1-broonie@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-4.7 required=5.0 tests=BAYES_00, KAM_DMARC_STATUS, NICE_REPLY_A, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham 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: Thu, 10 Jun 2021 17:02:15 -0000 Hi, On 6/4/21 6:24 AM, Mark Brown wrote: > Deployments of BTI on arm64 have run into issues interacting with > systemd's MemoryDenyWriteExecute feature. Currently for dynamically > linked executables the kernel will only handle architecture specific > properties like BTI for the interpreter, the expectation is that the > interpreter will then handle any properties on the main executable. > For BTI this means remapping the executable segments PROT_EXEC | > PROT_BTI. > > This interacts poorly with MemoryDenyWriteExecute since that is > implemented using a seccomp filter which prevents setting PROT_EXEC on > already mapped memory and lacks the context to be able to detect that > memory is already mapped with PROT_EXEC. This series resolves this by > handling the BTI property for both the interpreter and the main > executable. I've got a Fedora34 system booting in qemu or a model with BTI enabled. On that system I took the systemd-resolved executable, which is one of the services with MDWE enabled, and replaced a number of the bti's with nops. I expect the service to continue to work with the fedora or mainline 5.13 kernel and it does. If instead I boot with MDWE=no for the service, it should fail to start given either of those kernels, and it does. Thus, I expect that with his patch applied to 5.13 the service will fail to start regardless of the state of MDWE, but it seems to continue starting when I set MDWE=yes. Same behavior with v1 FWTW. Of course, there is a good chance I've messed something up or i'm missing something. I should really validate the /lib/ld-linux behavior itself too. I guess this could just as well be a glibc issue (f34 has glibc 2.33-5 which appears to have the re-mmap on failure patch). Either way, systemd-resolved is a LSB PIE, with /lib/ld-linux as its interpreter. I've not dug too deep into debugging this, cause I've got a couple other things I need to deal with in the next couple days, and I strongly dislike booting a full debug+system on the model. chuckle, sorry... Thanks, > > This does mean that we may get more code with BTI enabled if running on > a system without BTI support in the dynamic linker, this is expected to > be a safe configuration and testing seems to confirm that. It also > reduces the flexibility userspace has to disable BTI but it is expected > that for cases where there are problems which require BTI to be disabled > it is more likely that it will need to be disabled on a system level. > > v2: > - Add a patch dropping has_interp from arch_adjust_elf_prot() > - Fix bisection issue with static executables on arm64 in the first > patch. > > Mark Brown (3): > elf: Allow architectures to parse properties on the main executable > arm64: Enable BTI for main executable as well as the interpreter > elf: Remove has_interp property from arch_adjust_elf_prot() > > arch/arm64/include/asm/elf.h | 13 ++++++++++--- > arch/arm64/kernel/process.c | 20 +++++++------------- > fs/binfmt_elf.c | 29 ++++++++++++++++++++--------- > include/linux/elf.h | 8 +++++--- > 4 files changed, 42 insertions(+), 28 deletions(-) > > > base-commit: c4681547bcce777daf576925a966ffa824edd09d >