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=-11.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 27784C561F8 for ; Wed, 21 Oct 2020 12:43:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BF40422249 for ; Wed, 21 Oct 2020 12:43:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603284191; bh=ZmIu+Q0824rcpxnGkZoCPek2TdzzOtR/jSme+CHA5bQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=romAMzm1leTDNZ7SYUYYigLQPcIM8SeDj9gw3YlXNU2OkZRl6FVD3VfVSiaqP8C+a Jqudp1VamdXJB2l+zxS05L8z3yovmDylbRAUA1e8ut2xHtG8OQIGJOb5kInTjKdJsP fOYNUaGjbuflN2a5h7hT5nKOEEaXujJguU1iaxwI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2440828AbgJUMnJ (ORCPT ); Wed, 21 Oct 2020 08:43:09 -0400 Received: from mail.kernel.org ([198.145.29.99]:41464 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2395384AbgJUMnI (ORCPT ); Wed, 21 Oct 2020 08:43:08 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 05C772224E; Wed, 21 Oct 2020 12:43:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603284187; bh=ZmIu+Q0824rcpxnGkZoCPek2TdzzOtR/jSme+CHA5bQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=iwSyTn1+EMtVAgoC9GcdeyD5BvcxjSh3aZfbe6clNjU6dGSfkAGkBqPO6ktgEb5EW gALwNpb4eKnHa1Z1vTcSbbvQTzsJZ/GnQSHmybbpEnrwGDzFI+RaFaXPt0ywgsDUjT aiPvuEvSdNh84B1h7UGxrvz6N85yJNX5Ec6kwXK4= Date: Wed, 21 Oct 2020 13:43:02 +0100 From: Will Deacon To: Marc Zyngier Cc: Stephen Boyd , Catalin Marinas , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Andre Przywara , Steven Price , stable@vger.kernel.org Subject: Re: [PATCH 1/2] arm64: ARM_SMCCC_ARCH_WORKAROUND_1 doesn't return SMCCC_RET_NOT_REQUIRED Message-ID: <20201021124302.GA17804@willie-the-truck> References: <20201020214544.3206838-1-swboyd@chromium.org> <20201020214544.3206838-2-swboyd@chromium.org> <20201021075722.GA17230@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 21, 2020 at 11:23:34AM +0100, Marc Zyngier wrote: > On 2020-10-21 08:57, Will Deacon wrote: > > On Tue, Oct 20, 2020 at 02:45:43PM -0700, Stephen Boyd wrote: > > > According to the SMCCC spec (7.5.2 Discovery) the > > > ARM_SMCCC_ARCH_WORKAROUND_1 function id only returns 0, 1, and > > > SMCCC_RET_NOT_SUPPORTED corresponding to "workaround required", > > > "workaround not required but implemented", and "who knows, you're on > > > your own" respectively. For kvm hypercalls (hvc), we've implemented > > > this > > > function id to return SMCCC_RET_NOT_SUPPORTED, 1, and > > > SMCCC_RET_NOT_REQUIRED. The SMCCC_RET_NOT_REQUIRED return value is > > > not a > > > thing for this function id, and is probably copy/pasted from the > > > SMCCC_ARCH_WORKAROUND_2 function id that does support it. > > > > > > Clean this up by returning 0, 1, and SMCCC_RET_NOT_SUPPORTED > > > appropriately. Changing this exposes the problem that > > > spectre_v2_get_cpu_fw_mitigation_state() assumes a > > > SMCCC_RET_NOT_SUPPORTED return value means we are vulnerable, but > > > really > > > it means we have no idea and should assume we can't do anything about > > > mitigation. Put another way, it better be unaffected because it > > > can't be > > > mitigated in the firmware (in this case kvm) as the call isn't > > > implemented! > > > > > > Cc: Andre Przywara > > > Cc: Steven Price > > > Cc: Marc Zyngier > > > Cc: stable@vger.kernel.org > > > Fixes: c118bbb52743 ("arm64: KVM: Propagate full Spectre v2 > > > workaround state to KVM guests") > > > Fixes: 73f381660959 ("arm64: Advertise mitigation of Spectre-v2, or > > > lack thereof") > > > Signed-off-by: Stephen Boyd > > > --- > > > > > > This will require a slightly different backport to stable kernels, but > > > at least it looks like this is a problem given that this return value > > > isn't valid per the spec and we've been going around it by returning > > > something invalid for some time. > > > > > > arch/arm64/kernel/proton-pack.c | 3 +-- > > > arch/arm64/kvm/hypercalls.c | 2 +- > > > 2 files changed, 2 insertions(+), 3 deletions(-) > > > > > > diff --git a/arch/arm64/kernel/proton-pack.c > > > b/arch/arm64/kernel/proton-pack.c > > > index 68b710f1b43f..00bd54f63f4f 100644 > > > --- a/arch/arm64/kernel/proton-pack.c > > > +++ b/arch/arm64/kernel/proton-pack.c > > > @@ -149,10 +149,9 @@ static enum mitigation_state > > > spectre_v2_get_cpu_fw_mitigation_state(void) > > > case SMCCC_RET_SUCCESS: > > > return SPECTRE_MITIGATED; > > > case SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED: > > > + case SMCCC_RET_NOT_SUPPORTED: /* Good luck w/ the Gatekeeper of > > > Gozer */ > > > return SPECTRE_UNAFFECTED; > > > > Hmm, I'm not sure this is correct. The SMCCC spec is terrifically > > unhelpful: > > > > NOT_SUPPORTED: > > Either: > > * None of the PEs in the system require firmware mitigation for > > CVE-2017-5715. > > * The system contains at least 1 PE affected by CVE-2017-5715 that > > has no firmware > > mitigation available. > > * The firmware does not provide any information about whether > > firmware mitigation is > > required. > > > > so we can't tell whether the thing is vulnerable or not in this case, > > and > > have to assume that it is. > > > > > default: > > > - fallthrough; > > > - case SMCCC_RET_NOT_SUPPORTED: > > > return SPECTRE_VULNERABLE; > > > } > > > } > > > diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c > > > index 9824025ccc5c..868486957808 100644 > > > --- a/arch/arm64/kvm/hypercalls.c > > > +++ b/arch/arm64/kvm/hypercalls.c > > > @@ -31,7 +31,7 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu) > > > val = SMCCC_RET_SUCCESS; > > > break; > > > case SPECTRE_UNAFFECTED: > > > - val = SMCCC_RET_NOT_REQUIRED; > > > + val = SMCCC_RET_NOT_SUPPORTED; > > > > Which means we need to return SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED here, > > I > > suppose? > > Gahh, I keep mixing Spectre-v2 and WA2. Not good. I *think* the patch > below is enough, but I need to give it a go... Yeah, and me. We should've named them 2 and 4 back in the day. > diff --git a/arch/arm64/kernel/proton-pack.c > b/arch/arm64/kernel/proton-pack.c > index 68b710f1b43f..3f417d6305ef 100644 > --- a/arch/arm64/kernel/proton-pack.c > +++ b/arch/arm64/kernel/proton-pack.c > @@ -134,8 +134,6 @@ static enum mitigation_state > spectre_v2_get_cpu_hw_mitigation_state(void) > return SPECTRE_VULNERABLE; > } > > -#define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED (1) Unfortunately, I think this value _is_ specific to the ARCH_WORKAROUND calls, so it should stay like it is (i.e. other calls in SMCCC can return 1 to indicate other things) But the semantic bit here: > diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c > index 9824025ccc5c..792824de5d27 100644 > --- a/arch/arm64/kvm/hypercalls.c > +++ b/arch/arm64/kvm/hypercalls.c > @@ -31,7 +31,7 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu) > val = SMCCC_RET_SUCCESS; > break; > case SPECTRE_UNAFFECTED: > - val = SMCCC_RET_NOT_REQUIRED; > + val = SMCCC_RET_UNAFFECTED; Looks correct to me. Will