From patchwork Tue Apr 17 18:37:27 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Rutland X-Patchwork-Id: 10346459 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 4E1A560216 for ; Tue, 17 Apr 2018 18:38:55 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 3E3FD28615 for ; Tue, 17 Apr 2018 18:38:55 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 326D52861C; Tue, 17 Apr 2018 18:38:55 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=2.0 tests=BAYES_00, MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id 598D128618 for ; Tue, 17 Apr 2018 18:38:54 +0000 (UTC) Received: (qmail 25959 invoked by uid 550); 17 Apr 2018 18:38:08 -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: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 25850 invoked from network); 17 Apr 2018 18:38:07 -0000 From: Mark Rutland To: linux-arm-kernel@lists.infradead.org Cc: arnd@arndb.de, catalin.marinas@arm.com, cdall@kernel.org, drjones@redhat.com, kvmarm@lists.cs.columbia.edu, linux-arch@vger.kernel.org, marc.zyngier@arm.com, mark.rutland@arm.com, ramana.radhakrishnan@arm.com, suzuki.poulose@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, awallis@codeaurora.org, kernel-hardening@lists.openwall.com Subject: [PATCHv3 03/11] arm64/kvm: hide ptrauth from guests Date: Tue, 17 Apr 2018 19:37:27 +0100 Message-Id: <20180417183735.56985-4-mark.rutland@arm.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20180417183735.56985-1-mark.rutland@arm.com> References: <20180417183735.56985-1-mark.rutland@arm.com> X-Virus-Scanned: ClamAV using ClamSMTP 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. Signed-off-by: Mark Rutland Cc: Christoffer Dall Cc: Marc Zyngier Cc: kvmarm@lists.cs.columbia.edu Reviewed-by: Andrew Jones Reviewed-by: Christoffer Dall --- arch/arm64/kvm/handle_exit.c | 18 ++++++++++++++++++ arch/arm64/kvm/sys_regs.c | 9 +++++++++ 2 files changed, 27 insertions(+) diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c index e5e741bfffe1..5114ad691eae 100644 --- a/arch/arm64/kvm/handle_exit.c +++ b/arch/arm64/kvm/handle_exit.c @@ -173,6 +173,23 @@ static int handle_sve(struct kvm_vcpu *vcpu, struct kvm_run *run) return 1; } +/* + * Guest usage of a ptrauth instruction (which the guest EL1 did not turn into + * a NOP), or guest EL1 access to a ptrauth register. + */ +static int kvm_handle_ptrauth(struct kvm_vcpu *vcpu, struct kvm_run *run) +{ + /* + * We don't currently suport ptrauth in a guest, and we mask the ID + * registers to prevent well-behaved guests from trying to make use of + * it. + * + * Inject an UNDEF, as if the feature really isn't present. + */ + kvm_inject_undefined(vcpu); + return 1; +} + static exit_handle_fn arm_exit_handlers[] = { [0 ... ESR_ELx_EC_MAX] = kvm_handle_unknown_ec, [ESR_ELx_EC_WFx] = kvm_handle_wfx, @@ -195,6 +212,7 @@ static exit_handle_fn arm_exit_handlers[] = { [ESR_ELx_EC_BKPT32] = kvm_handle_guest_debug, [ESR_ELx_EC_BRK64] = kvm_handle_guest_debug, [ESR_ELx_EC_FP_ASIMD] = handle_no_fpsimd, + [ESR_ELx_EC_PAC] = kvm_handle_ptrauth, }; static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu) diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index 806b0b126a64..eee399c35e84 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -1000,6 +1000,15 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz) task_pid_nr(current)); val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT); + } else if (id == SYS_ID_AA64ISAR1_EL1) { + const u64 ptrauth_mask = (0xfUL << ID_AA64ISAR1_APA_SHIFT) | + (0xfUL << ID_AA64ISAR1_API_SHIFT) | + (0xfUL << ID_AA64ISAR1_GPA_SHIFT) | + (0xfUL << ID_AA64ISAR1_GPI_SHIFT); + if (val & ptrauth_mask) + pr_err_once("kvm [%i]: ptrauth unsupported for guests, suppressing\n", + task_pid_nr(current)); + val &= ~ptrauth_mask; } else if (id == SYS_ID_AA64MMFR1_EL1) { if (val & (0xfUL << ID_AA64MMFR1_LOR_SHIFT)) pr_err_once("kvm [%i]: LORegions unsupported for guests, suppressing\n",