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Sun, 09 Dec 2018 06:53:23 -0800 (PST) Subject: Re: [PATCH v6 04/13] arm64/kvm: hide ptrauth from guests To: Kristina Martsenko , linux-arm-kernel@lists.infradead.org References: <20181207183931.4285-1-kristina.martsenko@arm.com> <20181207183931.4285-5-kristina.martsenko@arm.com> From: Richard Henderson Openpgp: preference=signencrypt Message-ID: <57966497-d21c-5439-e4ba-d75f5552282f@linaro.org> Date: Sun, 9 Dec 2018 08:53:19 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 MIME-Version: 1.0 In-Reply-To: <20181207183931.4285-5-kristina.martsenko@arm.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20181209_065334_920109_462B44C5 X-CRM114-Status: GOOD ( 16.81 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Andrew Jones , Jacob Bramley , Ard Biesheuvel , Marc Zyngier , Catalin Marinas , Adam Wallis , Suzuki K Poulose , Will Deacon , Christoffer Dall , kvmarm@lists.cs.columbia.edu, Cyrill Gorcunov , Ramana Radhakrishnan , Amit Kachhap , Dave P Martin , linux-kernel@vger.kernel.org, Kees Cook Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 12/7/18 12:39 PM, Kristina Martsenko wrote: > From: Mark Rutland > > In subsequent patches we're going to expose ptrauth to the host kernel > and userspace, but things are a bit trickier for guest kernels. For the > time being, let's hide ptrauth from KVM guests. > > Regardless of how well-behaved the guest kernel is, guest userspace > could attempt to use ptrauth instructions, triggering a trap to EL2, > resulting in noise from kvm_handle_unknown_ec(). So let's write up a > handler for the PAC trap, which silently injects an UNDEF into the > guest, as if the feature were really missing. Reviewing the long thread that accompanied v5, I thought we were *not* going to trap PAuth instructions from the guest. In particular, the OS distribution may legitimately be built to include hint-space nops. This includes XPACLRI, which is used by the C++ exception unwinder and not controlled by SCTLR_EL1.EnI{A,B}. It seems like the header comment here, and > +/* > + * Guest usage of a ptrauth instruction (which the guest EL1 did not turn into > + * a NOP). > + */ > +static int kvm_handle_ptrauth(struct kvm_vcpu *vcpu, struct kvm_run *run) > + here, need updating. r~ _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel