From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AIpwx4+aq3Hyw4KkXgXlJVaFPTTA3g9aMslPPpQGBX71wk/sQhb4EbecRYJLelJ7QKZ/OeypFj2E ARC-Seal: i=1; a=rsa-sha256; t=1524057591; cv=none; d=google.com; s=arc-20160816; b=qvuc1uy+YmZcy/eMCQRB4TbGf8WReJmwU5Rz1p5Mozgk2iOG+SJaHsg4hJ6lm6jwsO 2nAscqwHpXPqLPaUreq5veelWCpq0hrgqhM/kFeX1u0B+FleuwscJPfM0GCOx9B9wuEP 9OuL+dS8DLMfgMCEvS6+JgmfPhvjmiwYR/3cKnoZr9ZL3oJ1HCDxVM0WWRz06AuvHkNI 7M5Y9XkCYFYiY7H6Z5SJuora3pXtiMdGPReIx4uVPCr4aUMDsBQM7qNOsEOAaluvJYmd sBmXKBcOpeP2PtsMyOn28Dfh3i/WJQBOPoyU+4qBUdCkNOCoe3sp1JTa8xq0FyUKcuFe oJ+w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:delivered-to:list-id :list-subscribe:list-unsubscribe:list-help:list-post:precedence :mailing-list:arc-authentication-results; bh=uYreU8C+nCvvHdeTlIg9IcLOT6AbesCb6cDIITfO3BU=; b=lQeADtD80BI9WMD/2GA2aFUXLY0ONZBexhV+LIJafrkNfvTxYrM+OcWq9Cz5BC3O6e Y8vnk2TXdj611dNE4/gZG1i/xv3W+QZy5NwdDwU4TCm4B5rv+3AIBvvzn62XDBh9mH0C FAl7lfXqary9qpf5jEwm7vIGaRqrwXwVQlakvfQ42zH4ZO8u0nmdfWFse9SaHYUZv9Wi oWU8/llczIeU2S3I45Cd1e93xCLEI9diLmK/z22fa7WuJg7pVXvonferWxTS66mAMks4 41pw5z0QdK/2ocoief24qP5WGDOgu7Zmxar1SlBQCdcPR47RkmKyP8hmY7v0AQJvvO21 bs8A== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of kernel-hardening-return-13037-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-13037-gregkh=linuxfoundation.org@lists.openwall.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=redhat.com Authentication-Results: mx.google.com; spf=pass (google.com: domain of kernel-hardening-return-13037-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-13037-gregkh=linuxfoundation.org@lists.openwall.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=redhat.com Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm List-Post: List-Help: List-Unsubscribe: List-Subscribe: Date: Wed, 18 Apr 2018 15:19:26 +0200 From: Andrew Jones To: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, arnd@arndb.de, catalin.marinas@arm.com, cdall@kernel.org, kvmarm@lists.cs.columbia.edu, linux-arch@vger.kernel.org, marc.zyngier@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: Re: [PATCHv3 03/11] arm64/kvm: hide ptrauth from guests Message-ID: <20180418131926.pbjlbcjspg7azq2j@kamzik.brq.redhat.com> References: <20180417183735.56985-1-mark.rutland@arm.com> <20180417183735.56985-4-mark.rutland@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180417183735.56985-4-mark.rutland@arm.com> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1598019694139875288?= X-GMAIL-MSGID: =?utf-8?q?1598090213329566824?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Tue, Apr 17, 2018 at 07:37:27PM +0100, Mark Rutland wrote: > 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 > --- > 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)); Marc just changed the equivalent SVE pr_err_once() to kvm_debug(). So we probably want to do the same here. > + 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", > -- > 2.11.0 > Otherwise Reviewed-by: Andrew Jones