From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D74F24156C3 for ; Mon, 20 Jul 2026 12:21:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784550106; cv=none; b=nAgmLcbwHdMP+uBTMekaPOiIf1ebIjpyqdVYB5ItWpkpfhWl/lDkmqV95fe/UuccvZO4LfLoJLjBZFMrPErG5CTWmHS9MNUB6wHU1hivhCmqUqFswhKPkTyPLzMRKomLbX4aSekNuQckoSQJHOhNOt4gSx/LO3UVCYJIidpM+uA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784550106; c=relaxed/simple; bh=UT9zzlJZ4LmBDvkvul2hFc+TLZeZYdaWmOTYtnVzcmU=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=Pl+rnVYVzY3Y4teT8L2qdWpPzpluxt4swmvm4RT+HiMajeG8j1In2NGZRjsSklYDhjiFl1aNqD9URatGb1N+jXBFYuHM8iEE3IvoCKcXV8L/S4uLRo4YzIRD5zRk+fMta2FUOQTzJzbc3AAB9wNeJleUCpjiFcJaFboVQuEpI+A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=RAvC/d5H; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="RAvC/d5H" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3DA7B1F00A3A; Mon, 20 Jul 2026 12:21:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784550104; bh=uoO61hD9TYt4EzH2dVlBQ3oggO+/vvnALr28qzOkdL4=; h=Subject:To:Cc:From:Date; b=RAvC/d5HDgTnXFXf16nu9YdBUygAri9cSWvr3RbOmXs+4ZVhEH5saNDEdP4cQXRsv KqbnPm6prHYWa7MTTsMWTkRdPIq3MsjD3dyCFV0X7yZHliRg8FoCYYLHEgtQXLC+uy Hlocu7w379Q/PSgQLMAqvCX1kiaasy7n8sB4WpCg= Subject: FAILED: patch "[PATCH] KVM: nVMX: Don't use vmcs01.GUEST_CR3 to snapshot L1's CR3" failed to apply to 5.15-stable tree To: seanjc@google.com,jmattson@google.com Cc: From: Date: Mon, 20 Jul 2026 14:21:17 +0200 Message-ID: <2026072017-staff-crimson-a48c@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 3e6dd2b9b7b2884743ed7a0873b8743cc0df6d40 # git commit -s git send-email --to '' --in-reply-to '2026072017-staff-crimson-a48c@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 3e6dd2b9b7b2884743ed7a0873b8743cc0df6d40 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 12 Jun 2026 07:56:42 -0700 Subject: [PATCH] KVM: nVMX: Don't use vmcs01.GUEST_CR3 to snapshot L1's CR3 when EPT is disabled Add a dedicated field in "struct nested_vmx" to track L1's pre-VM-Enter CR3 instead of using vmcs01.GUEST_CR3, which isn't anywhere near as safe as the comment purports it to be. E.g. in addition to the warn_on_missed_cc bug (that was fixed by relocating the consistency check), if getting vmcs12 pages (during actual nested VM-Entry) fails and EPT is disabled (in KVM), KVM will return control to userspace with vmcs01.GUEST_CR3 holding a guest- controlled value. Alternatively, KVM could force a reload of vmcs01.GUEST_CR3 by resetting the MMU context in the error path, but as above, the safety of the vmcs01 approach is extremely questionable, e.g. it took all of ~4 months for the code to break. Fixes: 671ddc700fd0 ("KVM: nVMX: Don't leak L1 MMIO regions to L2") Cc: stable@vger.kernel.org Cc: Jim Mattson Link: https://patch.msgid.link/20260612145642.452392-3-seanjc@google.com Signed-off-by: Sean Christopherson diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 4fc4349810a3..bb0eb40b4448 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -3658,19 +3658,14 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu, &vmx->nested.pre_vmenter_ssp_tbl); /* - * Overwrite vmcs01.GUEST_CR3 with L1's CR3 if EPT is disabled. In the - * event of a "late" VM-Fail, i.e. a VM-Fail detected by hardware but - * not KVM, KVM must unwind its software model to the pre-VM-Entry host - * state. When EPT is disabled, GUEST_CR3 holds KVM's shadow CR3, not - * L1's "real" CR3, which causes nested_vmx_restore_host_state() to - * corrupt vcpu->arch.cr3. Stuffing vmcs01.GUEST_CR3 results in the - * unwind naturally setting arch.cr3 to the correct value. Smashing - * vmcs01.GUEST_CR3 is safe because nested VM-Exits, and the unwind, - * reset KVM's MMU, i.e. vmcs01.GUEST_CR3 is guaranteed to be - * overwritten with a shadow CR3 prior to re-entering L1. + * Stash L1's CR3, so that in the event of a "late" VM-Fail, i.e. a + * VM-Fail detected by hardware but not KVM, KVM can unwind its + * software model to the pre-VM-Entry host state. When EPT is + * disabled, GUEST_CR3 holds KVM's shadow CR3, not L1's "real" CR3, + * and so simply restoring from vmcs01.GUEST_CR3 would corrupt + * vcpu->arch.cr3. */ - if (!enable_ept) - vmcs_writel(GUEST_CR3, vcpu->arch.cr3); + vmx->nested.pre_vmenter_cr3 = kvm_read_cr3(vcpu); vmx_switch_vmcs(vcpu, &vmx->nested.vmcs02); @@ -4982,7 +4977,7 @@ static void nested_vmx_restore_host_state(struct kvm_vcpu *vcpu) vmx_set_cr4(vcpu, vmcs_readl(CR4_READ_SHADOW)); nested_ept_uninit_mmu_context(vcpu); - vcpu->arch.cr3 = vmcs_readl(GUEST_CR3); + vcpu->arch.cr3 = vmx->nested.pre_vmenter_cr3; kvm_register_mark_available(vcpu, VCPU_REG_CR3); /* diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index de9de0d2016c..dc8517f15bc4 100644 --- a/arch/x86/kvm/vmx/vmx.h +++ b/arch/x86/kvm/vmx/vmx.h @@ -159,6 +159,13 @@ struct nested_vmx { bool has_preemption_timer_deadline; bool preemption_timer_expired; + /* + * Used to restore L1's CR3 if hardware detects a VM-Fail Consistency + * Check that KVM does not, in which case KVM needs to unwind CR3 back + * to its pre-VM-Enter state, NOT to vmcs01.HOST_CR3. + */ + unsigned long pre_vmenter_cr3; + /* * Used to snapshot MSRs that are conditionally loaded on VM-Enter in * order to propagate the guest's pre-VM-Enter value into vmcs02. For