From patchwork Tue Apr 26 08:22:05 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 567791 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 7336DC433FE for ; Tue, 26 Apr 2022 09:09:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346955AbiDZJMS (ORCPT ); Tue, 26 Apr 2022 05:12:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39728 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346277AbiDZJH3 (ORCPT ); Tue, 26 Apr 2022 05:07:29 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 46D04CC53F; Tue, 26 Apr 2022 01:48:36 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id D71E760C42; Tue, 26 Apr 2022 08:48:35 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D64FFC385A4; Tue, 26 Apr 2022 08:48:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1650962915; bh=Yo5ElvkPW5uz/nsLviwvUNIFZpOzBi2hvJAW0IiEdbI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ge0F6QyHWgG9ZjaZAJtX3IGOoD+sshZtOLpnQ1XXPRqWA16biLkwWOaY3llipzwt5 rGl0lORQnlq+r576lG9Tfz/DbFqrRqiXWtFFoYJhDxFEECdgGnTZR2fYuTEJsKKj/f oclpFU/TUecCQyltk8tlXm6s1D+QsiaCm829XKLI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Gaoning Pan , Yongkang Jia , Maxim Levitsky , Sean Christopherson , Paolo Bonzini Subject: [PATCH 5.17 130/146] KVM: x86: Pend KVM_REQ_APICV_UPDATE during vCPU creation to fix a race Date: Tue, 26 Apr 2022 10:22:05 +0200 Message-Id: <20220426081753.715426184@linuxfoundation.org> X-Mailer: git-send-email 2.36.0 In-Reply-To: <20220426081750.051179617@linuxfoundation.org> References: <20220426081750.051179617@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Sean Christopherson commit 423ecfea77dda83823c71b0fad1c2ddb2af1e5fc upstream. Make a KVM_REQ_APICV_UPDATE request when creating a vCPU with an in-kernel local APIC and APICv enabled at the module level. Consuming kvm_apicv_activated() and stuffing vcpu->arch.apicv_active directly can race with __kvm_set_or_clear_apicv_inhibit(), as vCPU creation happens before the vCPU is fully onlined, i.e. it won't get the request made to "all" vCPUs. If APICv is globally inhibited between setting apicv_active and onlining the vCPU, the vCPU will end up running with APICv enabled and trigger KVM's sanity check. Mark APICv as active during vCPU creation if APICv is enabled at the module level, both to be optimistic about it's final state, e.g. to avoid additional VMWRITEs on VMX, and because there are likely bugs lurking since KVM checks apicv_active in multiple vCPU creation paths. While keeping the current behavior of consuming kvm_apicv_activated() is arguably safer from a regression perspective, force apicv_active so that vCPU creation runs with deterministic state and so that if there are bugs, they are found sooner than later, i.e. not when some crazy race condition is hit. WARNING: CPU: 0 PID: 484 at arch/x86/kvm/x86.c:9877 vcpu_enter_guest+0x2ae3/0x3ee0 arch/x86/kvm/x86.c:9877 Modules linked in: CPU: 0 PID: 484 Comm: syz-executor361 Not tainted 5.16.13 #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1~cloud0 04/01/2014 RIP: 0010:vcpu_enter_guest+0x2ae3/0x3ee0 arch/x86/kvm/x86.c:9877 Call Trace: vcpu_run arch/x86/kvm/x86.c:10039 [inline] kvm_arch_vcpu_ioctl_run+0x337/0x15e0 arch/x86/kvm/x86.c:10234 kvm_vcpu_ioctl+0x4d2/0xc80 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3727 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:874 [inline] __se_sys_ioctl fs/ioctl.c:860 [inline] __x64_sys_ioctl+0x16d/0x1d0 fs/ioctl.c:860 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae The bug was hit by a syzkaller spamming VM creation with 2 vCPUs and a call to KVM_SET_GUEST_DEBUG. r0 = openat$kvm(0xffffffffffffff9c, &(0x7f0000000000), 0x0, 0x0) r1 = ioctl$KVM_CREATE_VM(r0, 0xae01, 0x0) ioctl$KVM_CAP_SPLIT_IRQCHIP(r1, 0x4068aea3, &(0x7f0000000000)) (async) r2 = ioctl$KVM_CREATE_VCPU(r1, 0xae41, 0x0) (async) r3 = ioctl$KVM_CREATE_VCPU(r1, 0xae41, 0x400000000000002) ioctl$KVM_SET_GUEST_DEBUG(r3, 0x4048ae9b, &(0x7f00000000c0)={0x5dda9c14aa95f5c5}) ioctl$KVM_RUN(r2, 0xae80, 0x0) Reported-by: Gaoning Pan Reported-by: Yongkang Jia Fixes: 8df14af42f00 ("kvm: x86: Add support for dynamic APICv activation") Cc: stable@vger.kernel.org Cc: Maxim Levitsky Signed-off-by: Sean Christopherson Reviewed-by: Maxim Levitsky Message-Id: <20220420013732.3308816-4-seanjc@google.com> Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/x86.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11113,8 +11113,21 @@ int kvm_arch_vcpu_create(struct kvm_vcpu r = kvm_create_lapic(vcpu, lapic_timer_advance_ns); if (r < 0) goto fail_mmu_destroy; - if (kvm_apicv_activated(vcpu->kvm)) + + /* + * Defer evaluating inhibits until the vCPU is first run, as + * this vCPU will not get notified of any changes until this + * vCPU is visible to other vCPUs (marked online and added to + * the set of vCPUs). Opportunistically mark APICv active as + * VMX in particularly is highly unlikely to have inhibits. + * Ignore the current per-VM APICv state so that vCPU creation + * is guaranteed to run with a deterministic value, the request + * will ensure the vCPU gets the correct state before VM-Entry. + */ + if (enable_apicv) { vcpu->arch.apicv_active = true; + kvm_make_request(KVM_REQ_APICV_UPDATE, vcpu); + } } else static_branch_inc(&kvm_has_noapic_vcpu);