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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 6B30EC433E1 for ; Thu, 4 Jun 2020 15:04:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4BAF9207D8 for ; Thu, 4 Jun 2020 15:04:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729348AbgFDPEm (ORCPT ); Thu, 4 Jun 2020 11:04:42 -0400 Received: from foss.arm.com ([217.140.110.172]:45508 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729162AbgFDPEm (ORCPT ); Thu, 4 Jun 2020 11:04:42 -0400 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 A52571FB; Thu, 4 Jun 2020 08:04:41 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.9.165]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2BA053F305; Thu, 4 Jun 2020 08:04:38 -0700 (PDT) Date: Thu, 4 Jun 2020 16:04:36 +0100 From: Mark Rutland To: Marc Zyngier Cc: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, James Morse , Julien Thierry , Suzuki K Poulose , Will Deacon , Catalin Marinas , kernel-team@android.com, stable@vger.kernel.org Subject: Re: [PATCH 1/3] KVM: arm64: Save the host's PtrAuth keys in non-preemptible context Message-ID: <20200604150436.GC75320@C02TD0UTHF1T.local> References: <20200604133354.1279412-1-maz@kernel.org> <20200604133354.1279412-2-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200604133354.1279412-2-maz@kernel.org> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Jun 04, 2020 at 02:33:52PM +0100, Marc Zyngier wrote: > When using the PtrAuth feature in a guest, we need to save the host's > keys before allowing the guest to program them. For that, we dump > them in a per-CPU data structure (the so called host context). > > But both call sites that do this are in preemptible context, > which may end up in disaster should the vcpu thread get preempted > before reentering the guest. Yuck! > Instead, save the keys eagerly on each vcpu_load(). This has an > increased overhead, but is at least safe. > > Cc: stable@vger.kernel.org > Signed-off-by: Marc Zyngier This looks sound to me given kvm_arch_vcpu_load() is surrounded with get_cpu() .. put_cpu() and gets called when the thread is preempted. Reviewed-by: Mark Rutland Thanks, Mark. > --- > arch/arm64/include/asm/kvm_emulate.h | 6 ------ > arch/arm64/kvm/arm.c | 18 +++++++++++++++++- > arch/arm64/kvm/handle_exit.c | 19 ++----------------- > 3 files changed, 19 insertions(+), 24 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h > index a30b4eec7cb4..977843e4d5fb 100644 > --- a/arch/arm64/include/asm/kvm_emulate.h > +++ b/arch/arm64/include/asm/kvm_emulate.h > @@ -112,12 +112,6 @@ static inline void vcpu_ptrauth_disable(struct kvm_vcpu *vcpu) > vcpu->arch.hcr_el2 &= ~(HCR_API | HCR_APK); > } > > -static inline void vcpu_ptrauth_setup_lazy(struct kvm_vcpu *vcpu) > -{ > - if (vcpu_has_ptrauth(vcpu)) > - vcpu_ptrauth_disable(vcpu); > -} > - > static inline unsigned long vcpu_get_vsesr(struct kvm_vcpu *vcpu) > { > return vcpu->arch.vsesr_el2; > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index d6988401c22a..152049c5055d 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -337,6 +337,12 @@ void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) > preempt_enable(); > } > > +#define __ptrauth_save_key(regs, key) \ > +({ \ > + regs[key ## KEYLO_EL1] = read_sysreg_s(SYS_ ## key ## KEYLO_EL1); \ > + regs[key ## KEYHI_EL1] = read_sysreg_s(SYS_ ## key ## KEYHI_EL1); \ > +}) > + > void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) > { > int *last_ran; > @@ -370,7 +376,17 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) > else > vcpu_set_wfx_traps(vcpu); > > - vcpu_ptrauth_setup_lazy(vcpu); > + if (vcpu_has_ptrauth(vcpu)) { > + struct kvm_cpu_context *ctxt = vcpu->arch.host_cpu_context; > + > + __ptrauth_save_key(ctxt->sys_regs, APIA); > + __ptrauth_save_key(ctxt->sys_regs, APIB); > + __ptrauth_save_key(ctxt->sys_regs, APDA); > + __ptrauth_save_key(ctxt->sys_regs, APDB); > + __ptrauth_save_key(ctxt->sys_regs, APGA); > + > + vcpu_ptrauth_disable(vcpu); > + } > } > > void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c > index eb194696ef62..065251efa2e6 100644 > --- a/arch/arm64/kvm/handle_exit.c > +++ b/arch/arm64/kvm/handle_exit.c > @@ -162,31 +162,16 @@ static int handle_sve(struct kvm_vcpu *vcpu, struct kvm_run *run) > return 1; > } > > -#define __ptrauth_save_key(regs, key) \ > -({ \ > - regs[key ## KEYLO_EL1] = read_sysreg_s(SYS_ ## key ## KEYLO_EL1); \ > - regs[key ## KEYHI_EL1] = read_sysreg_s(SYS_ ## key ## KEYHI_EL1); \ > -}) > - > /* > * Handle the guest trying to use a ptrauth instruction, or trying to access a > * ptrauth register. > */ > void kvm_arm_vcpu_ptrauth_trap(struct kvm_vcpu *vcpu) > { > - struct kvm_cpu_context *ctxt; > - > - if (vcpu_has_ptrauth(vcpu)) { > + if (vcpu_has_ptrauth(vcpu)) > vcpu_ptrauth_enable(vcpu); > - ctxt = vcpu->arch.host_cpu_context; > - __ptrauth_save_key(ctxt->sys_regs, APIA); > - __ptrauth_save_key(ctxt->sys_regs, APIB); > - __ptrauth_save_key(ctxt->sys_regs, APDA); > - __ptrauth_save_key(ctxt->sys_regs, APDB); > - __ptrauth_save_key(ctxt->sys_regs, APGA); > - } else { > + else > kvm_inject_undefined(vcpu); > - } > } > > /* > -- > 2.26.2 >