From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Martin Subject: Re: [PATCH v10 2/5] KVM: arm/arm64: context-switch ptrauth registers Date: Wed, 24 Apr 2019 14:39:06 +0100 Message-ID: <20190424133903.GU3567@e103592.cambridge.arm.com> References: <1555994558-26349-1-git-send-email-amit.kachhap@arm.com> <1555994558-26349-3-git-send-email-amit.kachhap@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1555994558-26349-3-git-send-email-amit.kachhap@arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Amit Daniel Kachhap Cc: linux-arm-kernel@lists.infradead.org, Marc Zyngier , Catalin Marinas , Will Deacon , Kristina Martsenko , kvmarm@lists.cs.columbia.edu, Ramana Radhakrishnan , linux-kernel@vger.kernel.org List-Id: kvmarm@lists.cs.columbia.edu On Tue, Apr 23, 2019 at 10:12:35AM +0530, Amit Daniel Kachhap wrote: > From: Mark Rutland > > When pointer authentication is supported, a guest may wish to use it. > This patch adds the necessary KVM infrastructure for this to work, with > a semi-lazy context switch of the pointer auth state. > > Pointer authentication feature is only enabled when VHE is built > in the kernel and present in the CPU implementation so only VHE code > paths are modified. > > When we schedule a vcpu, we disable guest usage of pointer > authentication instructions and accesses to the keys. While these are > disabled, we avoid context-switching the keys. When we trap the guest > trying to use pointer authentication functionality, we change to eagerly > context-switching the keys, and enable the feature. The next time the > vcpu is scheduled out/in, we start again. However the host key save is > optimized and implemented inside ptrauth instruction/register access > trap. > > Pointer authentication consists of address authentication and generic > authentication, and CPUs in a system might have varied support for > either. Where support for either feature is not uniform, it is hidden > from guests via ID register emulation, as a result of the cpufeature > framework in the host. > > Unfortunately, address authentication and generic authentication cannot > be trapped separately, as the architecture provides a single EL2 trap > covering both. If we wish to expose one without the other, we cannot > prevent a (badly-written) guest from intermittently using a feature > which is not uniformly supported (when scheduled on a physical CPU which > supports the relevant feature). Hence, this patch expects both type of > authentication to be present in a cpu. > > This switch of key is done from guest enter/exit assembly as preparation > for the upcoming in-kernel pointer authentication support. Hence, these > key switching routines are not implemented in C code as they may cause > pointer authentication key signing error in some situations. > > Signed-off-by: Mark Rutland > [Only VHE, key switch in full assembly, vcpu_has_ptrauth checks > , save host key in ptrauth exception trap] > Signed-off-by: Amit Daniel Kachhap > Reviewed-by: Julien Thierry > Cc: Marc Zyngier > Cc: Christoffer Dall > Cc: kvmarm@lists.cs.columbia.edu > --- > Changes since v9: > > * Removed hardcoding of enum values[Mark Zyngier]. > * Changed kvm_ptrauth_asm.h to kvm_ptrauth.h[Mark Zyngier]. > * Removed macro __ptrauth_save_state and applied inline [Marc Zyngier]. > * Moved kvm_arm_vcpu_ptrauth_setup_lazy, kvm_arm_vcpu_ptrauth_enable and > kvm_arm_vcpu_ptrauth_disable from *.c to kvm_emulate.h file [Marc Zyngier]. > * Added/Modified comments at few places [Marc Zyngier]. [...] > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c [...] > @@ -1058,9 +1087,11 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu, > (0xfUL << ID_AA64ISAR1_API_SHIFT) | > (0xfUL << ID_AA64ISAR1_GPA_SHIFT) | > (0xfUL << ID_AA64ISAR1_GPI_SHIFT); > - if (val & ptrauth_mask) > - kvm_debug("ptrauth unsupported for guests, suppressing\n"); > - val &= ~ptrauth_mask; > + if (!vcpu_has_ptrauth(vcpu)) { > + if (val & ptrauth_mask) > + kvm_debug("ptrauth unsupported for guests, suppressing\n"); > + val &= ~ptrauth_mask; > + } Hmmm, didn't spot this before, but this error message no longer makes sense now that KVM _does_ support pointer auth. Without vcpu_has_ptrauth(vcpu), we should just silently mask out the relevant ID fields now (same as for SVE). The patch below should achieve that. --8<-- >>From c6065122c5cccef57108dff990ce8fb43426f88e Mon Sep 17 00:00:00 2001 From: Dave Martin Date: Wed, 24 Apr 2019 14:32:29 +0100 Subject: [PATCH] KVM: arm64: sys_regs: Remove warning about missing pointer auth support KVM does support pointer auth for guests now, so it is inappropriate (and confusing) to print a warning to dmesg when userspace explicitly does not ask for pointer auth to be turned on for a vcpu. So, just squash the virtual ptrauth ID_AA64ISAR1_EL1 fields when appropriate and remove the warning. Signed-off-by: Dave Martin --- arch/arm64/kvm/sys_regs.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index 7f06c2e..f599f5e 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -1082,16 +1082,11 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu, if (id == SYS_ID_AA64PFR0_EL1 && !vcpu_has_sve(vcpu)) { 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 (!vcpu_has_ptrauth(vcpu)) { - if (val & ptrauth_mask) - kvm_debug("ptrauth unsupported for guests, suppressing\n"); - val &= ~ptrauth_mask; - } + } else if (id == SYS_ID_AA64ISAR1_EL1 && !vcpu_has_ptrauth(vcpu)) { + val &= ~((0xfUL << ID_AA64ISAR1_APA_SHIFT) | + (0xfUL << ID_AA64ISAR1_API_SHIFT) | + (0xfUL << ID_AA64ISAR1_GPA_SHIFT) | + (0xfUL << ID_AA64ISAR1_GPI_SHIFT)); } return val; -- 2.1.4 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 X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71C21C282CE for ; Wed, 24 Apr 2019 13:39:16 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 07C9D21773 for ; Wed, 24 Apr 2019 13:39:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 07C9D21773 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 797104A3B4; 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Wed, 24 Apr 2019 06:39:10 -0700 (PDT) Received: from e103592.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 84C993F238; Wed, 24 Apr 2019 06:39:08 -0700 (PDT) Date: Wed, 24 Apr 2019 14:39:06 +0100 From: Dave Martin To: Amit Daniel Kachhap Subject: Re: [PATCH v10 2/5] KVM: arm/arm64: context-switch ptrauth registers Message-ID: <20190424133903.GU3567@e103592.cambridge.arm.com> References: <1555994558-26349-1-git-send-email-amit.kachhap@arm.com> <1555994558-26349-3-git-send-email-amit.kachhap@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1555994558-26349-3-git-send-email-amit.kachhap@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Cc: Marc Zyngier , Catalin Marinas , Will Deacon , linux-kernel@vger.kernel.org, Kristina Martsenko , Ramana Radhakrishnan , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu Message-ID: <20190424133906.rVCcLrEtMPaOoSAwrJJ0xri7-9-MRuYzDeSFC8339W0@z> On Tue, Apr 23, 2019 at 10:12:35AM +0530, Amit Daniel Kachhap wrote: > From: Mark Rutland > > When pointer authentication is supported, a guest may wish to use it. > This patch adds the necessary KVM infrastructure for this to work, with > a semi-lazy context switch of the pointer auth state. > > Pointer authentication feature is only enabled when VHE is built > in the kernel and present in the CPU implementation so only VHE code > paths are modified. > > When we schedule a vcpu, we disable guest usage of pointer > authentication instructions and accesses to the keys. While these are > disabled, we avoid context-switching the keys. When we trap the guest > trying to use pointer authentication functionality, we change to eagerly > context-switching the keys, and enable the feature. The next time the > vcpu is scheduled out/in, we start again. However the host key save is > optimized and implemented inside ptrauth instruction/register access > trap. > > Pointer authentication consists of address authentication and generic > authentication, and CPUs in a system might have varied support for > either. Where support for either feature is not uniform, it is hidden > from guests via ID register emulation, as a result of the cpufeature > framework in the host. > > Unfortunately, address authentication and generic authentication cannot > be trapped separately, as the architecture provides a single EL2 trap > covering both. If we wish to expose one without the other, we cannot > prevent a (badly-written) guest from intermittently using a feature > which is not uniformly supported (when scheduled on a physical CPU which > supports the relevant feature). Hence, this patch expects both type of > authentication to be present in a cpu. > > This switch of key is done from guest enter/exit assembly as preparation > for the upcoming in-kernel pointer authentication support. Hence, these > key switching routines are not implemented in C code as they may cause > pointer authentication key signing error in some situations. > > Signed-off-by: Mark Rutland > [Only VHE, key switch in full assembly, vcpu_has_ptrauth checks > , save host key in ptrauth exception trap] > Signed-off-by: Amit Daniel Kachhap > Reviewed-by: Julien Thierry > Cc: Marc Zyngier > Cc: Christoffer Dall > Cc: kvmarm@lists.cs.columbia.edu > --- > Changes since v9: > > * Removed hardcoding of enum values[Mark Zyngier]. > * Changed kvm_ptrauth_asm.h to kvm_ptrauth.h[Mark Zyngier]. > * Removed macro __ptrauth_save_state and applied inline [Marc Zyngier]. > * Moved kvm_arm_vcpu_ptrauth_setup_lazy, kvm_arm_vcpu_ptrauth_enable and > kvm_arm_vcpu_ptrauth_disable from *.c to kvm_emulate.h file [Marc Zyngier]. > * Added/Modified comments at few places [Marc Zyngier]. [...] > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c [...] > @@ -1058,9 +1087,11 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu, > (0xfUL << ID_AA64ISAR1_API_SHIFT) | > (0xfUL << ID_AA64ISAR1_GPA_SHIFT) | > (0xfUL << ID_AA64ISAR1_GPI_SHIFT); > - if (val & ptrauth_mask) > - kvm_debug("ptrauth unsupported for guests, suppressing\n"); > - val &= ~ptrauth_mask; > + if (!vcpu_has_ptrauth(vcpu)) { > + if (val & ptrauth_mask) > + kvm_debug("ptrauth unsupported for guests, suppressing\n"); > + val &= ~ptrauth_mask; > + } Hmmm, didn't spot this before, but this error message no longer makes sense now that KVM _does_ support pointer auth. Without vcpu_has_ptrauth(vcpu), we should just silently mask out the relevant ID fields now (same as for SVE). The patch below should achieve that. --8<-- >From c6065122c5cccef57108dff990ce8fb43426f88e Mon Sep 17 00:00:00 2001 From: Dave Martin Date: Wed, 24 Apr 2019 14:32:29 +0100 Subject: [PATCH] KVM: arm64: sys_regs: Remove warning about missing pointer auth support KVM does support pointer auth for guests now, so it is inappropriate (and confusing) to print a warning to dmesg when userspace explicitly does not ask for pointer auth to be turned on for a vcpu. So, just squash the virtual ptrauth ID_AA64ISAR1_EL1 fields when appropriate and remove the warning. Signed-off-by: Dave Martin --- arch/arm64/kvm/sys_regs.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index 7f06c2e..f599f5e 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -1082,16 +1082,11 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu, if (id == SYS_ID_AA64PFR0_EL1 && !vcpu_has_sve(vcpu)) { 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 (!vcpu_has_ptrauth(vcpu)) { - if (val & ptrauth_mask) - kvm_debug("ptrauth unsupported for guests, suppressing\n"); - val &= ~ptrauth_mask; - } + } else if (id == SYS_ID_AA64ISAR1_EL1 && !vcpu_has_ptrauth(vcpu)) { + val &= ~((0xfUL << ID_AA64ISAR1_APA_SHIFT) | + (0xfUL << ID_AA64ISAR1_API_SHIFT) | + (0xfUL << ID_AA64ISAR1_GPA_SHIFT) | + (0xfUL << ID_AA64ISAR1_GPI_SHIFT)); } return val; -- 2.1.4 _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm