From patchwork Mon Jan 24 13:05:32 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vitaly Kuznetsov X-Patchwork-Id: 536475 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 76B38C433F5 for ; Mon, 24 Jan 2022 13:05:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242880AbiAXNFq (ORCPT ); Mon, 24 Jan 2022 08:05:46 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:34793 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239721AbiAXNFp (ORCPT ); Mon, 24 Jan 2022 08:05:45 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1643029545; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=y9XdJI0onvJoCdSTO3zWbK1yaLtPTwQERDe6IWNipTs=; b=Ddx/TkVGO2bYsOe/+E9exP1QKCN3a0ar8HvF+ms5+y/Q1YGcTklaC5/gHLPaZaK3ZD16gp +FL2yDqLcg8B+2Bqd0xBzmYopncd7WyQqg1O2ZTUzyTS7kmzh4Zgi4N0GGlBgLlVcF2z5V FXzotygbLutmwhKGUXhzPwuKZ1hngFs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-362-KhRoKB50Me2Ib837t_6mug-1; Mon, 24 Jan 2022 08:05:42 -0500 X-MC-Unique: KhRoKB50Me2Ib837t_6mug-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0A7EB8143EB; Mon, 24 Jan 2022 13:05:41 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.40.194.235]) by smtp.corp.redhat.com (Postfix) with ESMTP id 70A0B7D533; Mon, 24 Jan 2022 13:05:39 +0000 (UTC) From: Vitaly Kuznetsov To: stable@vger.kernel.org Cc: Paolo Bonzini , Igor Mammedov , gregkh@linuxfoundation.org Subject: [PATCH stable 5.16 v1 2/4] KVM: x86: Partially allow KVM_SET_CPUID{,2} after KVM_RUN Date: Mon, 24 Jan 2022 14:05:32 +0100 Message-Id: <20220124130534.2645955-3-vkuznets@redhat.com> In-Reply-To: <20220124130534.2645955-1-vkuznets@redhat.com> References: <20220124130534.2645955-1-vkuznets@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org commit c6617c61e8fe44b9e9fdfede921f61cac6b5149d upstream. Commit feb627e8d6f6 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN") forbade changing CPUID altogether but unfortunately this is not fully compatible with existing VMMs. In particular, QEMU reuses vCPU fds for CPU hotplug after unplug and it calls KVM_SET_CPUID2. Instead of full ban, check whether the supplied CPUID data is equal to what was previously set. Reported-by: Igor Mammedov Fixes: feb627e8d6f6 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN") Signed-off-by: Vitaly Kuznetsov Message-Id: <20220117150542.2176196-3-vkuznets@redhat.com> Cc: stable@vger.kernel.org [Do not call kvm_find_cpuid_entry repeatedly. - Paolo] Signed-off-by: Paolo Bonzini Signed-off-by: Vitaly Kuznetsov --- arch/x86/kvm/cpuid.c | 36 ++++++++++++++++++++++++++++++++++++ arch/x86/kvm/x86.c | 19 ------------------- 2 files changed, 36 insertions(+), 19 deletions(-) diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index c4d4c350afbe..e5e597fc3c86 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -99,6 +99,28 @@ static int kvm_check_cpuid(struct kvm_cpuid_entry2 *entries, int nent) return 0; } +/* Check whether the supplied CPUID data is equal to what is already set for the vCPU. */ +static int kvm_cpuid_check_equal(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2, + int nent) +{ + struct kvm_cpuid_entry2 *orig; + int i; + + if (nent != vcpu->arch.cpuid_nent) + return -EINVAL; + + for (i = 0; i < nent; i++) { + orig = &vcpu->arch.cpuid_entries[i]; + if (e2[i].function != orig->function || + e2[i].index != orig->index || + e2[i].eax != orig->eax || e2[i].ebx != orig->ebx || + e2[i].ecx != orig->ecx || e2[i].edx != orig->edx) + return -EINVAL; + } + + return 0; +} + static void kvm_update_kvm_cpuid_base(struct kvm_vcpu *vcpu) { u32 function; @@ -293,6 +315,20 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2, __kvm_update_cpuid_runtime(vcpu, e2, nent); + /* + * KVM does not correctly handle changing guest CPUID after KVM_RUN, as + * MAXPHYADDR, GBPAGES support, AMD reserved bit behavior, etc.. aren't + * tracked in kvm_mmu_page_role. As a result, KVM may miss guest page + * faults due to reusing SPs/SPTEs. In practice no sane VMM mucks with + * the core vCPU model on the fly. It would've been better to forbid any + * KVM_SET_CPUID{,2} calls after KVM_RUN altogether but unfortunately + * some VMMs (e.g. QEMU) reuse vCPU fds for CPU hotplug/unplug and do + * KVM_SET_CPUID{,2} again. To support this legacy behavior, check + * whether the supplied CPUID data is equal to what's already set. + */ + if (vcpu->arch.last_vmentry_cpu != -1) + return kvm_cpuid_check_equal(vcpu, e2, nent); + r = kvm_check_cpuid(e2, nent); if (r) return r; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 0b5c61bb24a1..d8277a35dfb8 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5148,17 +5148,6 @@ long kvm_arch_vcpu_ioctl(struct file *filp, struct kvm_cpuid __user *cpuid_arg = argp; struct kvm_cpuid cpuid; - /* - * KVM does not correctly handle changing guest CPUID after KVM_RUN, as - * MAXPHYADDR, GBPAGES support, AMD reserved bit behavior, etc.. aren't - * tracked in kvm_mmu_page_role. As a result, KVM may miss guest page - * faults due to reusing SPs/SPTEs. In practice no sane VMM mucks with - * the core vCPU model on the fly, so fail. - */ - r = -EINVAL; - if (vcpu->arch.last_vmentry_cpu != -1) - goto out; - r = -EFAULT; if (copy_from_user(&cpuid, cpuid_arg, sizeof(cpuid))) goto out; @@ -5169,14 +5158,6 @@ long kvm_arch_vcpu_ioctl(struct file *filp, struct kvm_cpuid2 __user *cpuid_arg = argp; struct kvm_cpuid2 cpuid; - /* - * KVM_SET_CPUID{,2} after KVM_RUN is forbidded, see the comment in - * KVM_SET_CPUID case above. - */ - r = -EINVAL; - if (vcpu->arch.last_vmentry_cpu != -1) - goto out; - r = -EFAULT; if (copy_from_user(&cpuid, cpuid_arg, sizeof(cpuid))) goto out;