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 autolearn=ham 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 1EF85C433DF for ; Thu, 4 Jun 2020 15:23:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F205C206E6 for ; Thu, 4 Jun 2020 15:23:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729349AbgFDPXj (ORCPT ); Thu, 4 Jun 2020 11:23:39 -0400 Received: from foss.arm.com ([217.140.110.172]:45786 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728145AbgFDPXj (ORCPT ); Thu, 4 Jun 2020 11:23:39 -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 75CFE1FB; Thu, 4 Jun 2020 08:23:38 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.9.165]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3C8D93F305; Thu, 4 Jun 2020 08:23:36 -0700 (PDT) Date: Thu, 4 Jun 2020 16:23:33 +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 Subject: Re: [PATCH 2/3] KVM: arm64: Handle PtrAuth traps early Message-ID: <20200604152333.GD75320@C02TD0UTHF1T.local> References: <20200604133354.1279412-1-maz@kernel.org> <20200604133354.1279412-3-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200604133354.1279412-3-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 02:33:53PM +0100, Marc Zyngier wrote: > The current way we deal with PtrAuth is a bit heavy handed: > > - We forcefully save the host's keys on each vcpu_load() > - Handling the PtrAuth trap forces us to go all the way back > to the exit handling code to just set the HCR bits > > Overall, this is pretty heavy handed. A better approach would be > to handle it the same way we deal with the FPSIMD registers: > > - On vcpu_load() disable PtrAuth for the guest > - On first use, save the host's keys, enable PtrAuth in the > guest > > Crutially, this can happen as a fixup, which is done very early > on exit. We can then reenter the guest immediately without > leaving the hypervisor role. > > Another thing is that it simplify the rest of the host handling: > exiting all the way to the host means that the only possible > outcome for this trap is to inject an UNDEF. > > Signed-off-by: Marc Zyngier > --- > arch/arm64/kvm/arm.c | 17 +---------- > arch/arm64/kvm/handle_exit.c | 17 ++--------- > arch/arm64/kvm/hyp/switch.c | 59 ++++++++++++++++++++++++++++++++++++ > arch/arm64/kvm/sys_regs.c | 13 +++----- > 4 files changed, 68 insertions(+), 38 deletions(-) [...] > +static bool __hyp_text __hyp_handle_ptrauth(struct kvm_vcpu *vcpu) > +{ > + u32 sysreg = esr_sys64_to_sysreg(kvm_vcpu_get_hsr(vcpu)); > + u32 ec = kvm_vcpu_trap_get_class(vcpu); > + struct kvm_cpu_context *ctxt; > + u64 val; > + > + if (!vcpu_has_ptrauth(vcpu)) > + return false; > + > + switch (ec) { > + case ESR_ELx_EC_PAC: > + break; > + case ESR_ELx_EC_SYS64: > + switch (sysreg) { > + case SYS_APIAKEYLO_EL1: > + case SYS_APIAKEYHI_EL1: > + case SYS_APIBKEYLO_EL1: > + case SYS_APIBKEYHI_EL1: > + case SYS_APDAKEYLO_EL1: > + case SYS_APDAKEYHI_EL1: > + case SYS_APDBKEYLO_EL1: > + case SYS_APDBKEYHI_EL1: > + case SYS_APGAKEYLO_EL1: > + case SYS_APGAKEYHI_EL1: > + break; > + default: > + return false; > + } > + break; > + default: > + return false; > + } The ESR triage looks correct, but I think it might be clearer split out into a helper, since you can avoid the default cases with direct returns, and you could avoid the nested switch, e.g. static inline bool __hyp_text esr_is_ptrauth_trap(u32 esr) { u32 ec = ESR_ELx_EC(esr); if (ec == ESR_ELx_EC_PAC) return true; if (ec != ESR_ELx_EC_SYS64) return false; switch (esr_sys64_to_sysreg(esr)) { case SYS_APIAKEYLO_EL1: case SYS_APIAKEYHI_EL1: case SYS_APIBKEYLO_EL1: case SYS_APIBKEYHI_EL1: case SYS_APDAKEYLO_EL1: case SYS_APDAKEYHI_EL1: case SYS_APDBKEYLO_EL1: case SYS_APDBKEYHI_EL1: case SYS_APGAKEYLO_EL1: case SYS_APGAKEYHI_EL1: return true; } return false; } > + > + ctxt = kern_hyp_va(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_enable(vcpu); > + > + val = read_sysreg(hcr_el2); > + val |= (HCR_API | HCR_APK); > + write_sysreg(val, hcr_el2); > + > + return true; > +} > + > /* > * Return true when we were able to fixup the guest exit and should return to > * the guest, false when we should restore the host state and return to the > @@ -524,6 +580,9 @@ static bool __hyp_text fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code) > if (__hyp_handle_fpsimd(vcpu)) > return true; > > + if (__hyp_handle_ptrauth(vcpu)) > + return true; > + > if (!__populate_fault_info(vcpu)) > return true; > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > index ad1d57501d6d..564995084cf8 100644 > --- a/arch/arm64/kvm/sys_regs.c > +++ b/arch/arm64/kvm/sys_regs.c > @@ -1034,16 +1034,13 @@ static bool trap_ptrauth(struct kvm_vcpu *vcpu, > struct sys_reg_params *p, > const struct sys_reg_desc *rd) > { > - kvm_arm_vcpu_ptrauth_trap(vcpu); > - > /* > - * Return false for both cases as we never skip the trapped > - * instruction: > - * > - * - Either we re-execute the same key register access instruction > - * after enabling ptrauth. > - * - Or an UNDEF is injected as ptrauth is not supported/enabled. > + * If we land here, that is because we didn't fixup the access on exit > + * by allowing the PtrAuth sysregs. The only way this happens is when > + * the guest does not have PtrAuth support enabled. > */ > + kvm_inject_undefined(vcpu); > + > return false; > } > > -- > 2.26.2 > Regardless of the suggestion above, this looks sound to me. I agree that it's much nicer to handle this in hyp, and AFAICT the context switch should do the right thing, so: Reviewed-by: Mark Rutland Thanks, Mark.