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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 BC3EEC4CECE for ; Mon, 16 Sep 2019 19:12:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9B45F206C2 for ; Mon, 16 Sep 2019 19:12:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733257AbfIPTMT (ORCPT ); Mon, 16 Sep 2019 15:12:19 -0400 Received: from mga11.intel.com ([192.55.52.93]:18665 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727826AbfIPTMT (ORCPT ); Mon, 16 Sep 2019 15:12:19 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 16 Sep 2019 12:12:18 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,513,1559545200"; d="scan'208";a="187234562" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.41]) by fmsmga007.fm.intel.com with ESMTP; 16 Sep 2019 12:12:18 -0700 Date: Mon, 16 Sep 2019 12:12:18 -0700 From: Sean Christopherson To: Wanpeng Li Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , stable@vger.kernel.org Subject: Re: [PATCH] KVM: X86: Fix warning in handle_desc Message-ID: <20190916191218.GM18871@linux.intel.com> References: <1568617969-6934-1-git-send-email-wanpengli@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1568617969-6934-1-git-send-email-wanpengli@tencent.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Sep 16, 2019 at 03:12:49PM +0800, Wanpeng Li wrote: > From: Wanpeng Li > > Reported by syzkaller: > > WARNING: CPU: 0 PID: 6544 at /home/kernel/data/kvm/arch/x86/kvm//vmx/vmx.c:4689 handle_desc+0x37/0x40 [kvm_intel] > CPU: 0 PID: 6544 Comm: a.out Tainted: G OE 5.3.0-rc4+ #4 > RIP: 0010:handle_desc+0x37/0x40 [kvm_intel] > Call Trace: > vmx_handle_exit+0xbe/0x6b0 [kvm_intel] > vcpu_enter_guest+0x4dc/0x18d0 [kvm] > kvm_arch_vcpu_ioctl_run+0x407/0x660 [kvm] > kvm_vcpu_ioctl+0x3ad/0x690 [kvm] > do_vfs_ioctl+0xa2/0x690 > ksys_ioctl+0x6d/0x80 > __x64_sys_ioctl+0x1a/0x20 > do_syscall_64+0x74/0x720 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > When CR4.UMIP is set, guest should have UMIP cpuid flag. Current > kvm set_sregs function doesn't have such check when userspace inputs > sregs values. SECONDARY_EXEC_DESC is enabled on writes to CR4.UMIP in > vmx_set_cr4 though guest doesn't have UMIP cpuid flag. The testcast > triggers handle_desc warning when executing ltr instruction since guest > architectural CR4 doesn't set UMIP. This patch fixes it by adding check > for guest UMIP cpuid flag when get sreg inputs from userspace. > > Reported-by: syzbot+0f1819555fbdce992df9@syzkaller.appspotmail.com > Fixes: 0367f205a3b7 ("KVM: vmx: add support for emulating UMIP") > Cc: stable@vger.kernel.org > Signed-off-by: Wanpeng Li > --- > Note: syzbot report link https://lkml.org/lkml/2019/9/11/799 > > arch/x86/kvm/x86.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index f7cfd8e..83288ba 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -8645,6 +8645,10 @@ static int kvm_valid_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs) > (sregs->cr4 & X86_CR4_OSXSAVE)) > return -EINVAL; > > + if (!guest_cpuid_has(vcpu, X86_FEATURE_UMIP) && > + (sregs->cr4 & X86_CR4_UMIP)) Assuming vmx_set_cr4() fails because nested_cr4_valid() fails, isn't this a generic problem with nested VMX that just happens to be visible because of the WARN_ON() in handle_desc()? In general, KVM lets userspace set broken combinations of CPUID vs. CRx so that it doesn't dictate ordering, e.g. __set_sregs() intentionally calls kvm_x86_ops->set_cr4() instead of kvm_set_cr4(), which has all the CPUID checks. The existing OSXSAVE check in kvm_valid_sregs() is more about ensuring host support (see commit 6d1068b3a985, "KVM: x86: invalid opcode oops on SET_SREGS with OSXSAVE bit set (CVE-2012-4461)"). Given that both vmx_set_cr4() and svm_set_cr4() can return failure and cause __set_sregs() to silently fail, what about adding a new x86 ops to pre-check cr4, e.g. vm_x86_ops->is_valid_cr4(), and then WARN if set_cr4() fails during __set_sregs()? > + return -EINVAL; > + > if ((sregs->efer & EFER_LME) && (sregs->cr0 & X86_CR0_PG)) { > /* > * When EFER.LME and CR0.PG are set, the processor is in > -- > 2.7.4 >