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=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 D3B2AC4CECD for ; Tue, 17 Sep 2019 08:23:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A9E29218AC for ; Tue, 17 Sep 2019 08:23:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="DDWYxX6h" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730101AbfIQIXC (ORCPT ); Tue, 17 Sep 2019 04:23:02 -0400 Received: from mail-ot1-f66.google.com ([209.85.210.66]:40789 "EHLO mail-ot1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728123AbfIQIXB (ORCPT ); Tue, 17 Sep 2019 04:23:01 -0400 Received: by mail-ot1-f66.google.com with SMTP id y39so2264856ota.7; Tue, 17 Sep 2019 01:23:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=pAhRX1Y8hlT53IJmsS9eKDWXvMfY7PiqTbL9YMzPsQY=; b=DDWYxX6hEtoMmfBPsku/8mPtsbFfVqOuH6B5K6Rf5504uIFWUvA4nKyX7p9UOK5QL9 x00eSKjYfX43V6lfKBKhbU6aD4TiaoRI8Bf195GYRbRSYcqm1AAyTMa5Wc/qzWj/GevV D28/qLQapOc2Bs9o/O7CMpq5wkgSVuklj54vaUnWaer7QFf+EAIxYyhJYizmV1dTIsRx FI8pmaCUWrzXu5/4stOiThInpHgBqPjL3Tc64msxMkJ6PjLhP75UZJHMxivCJJpLJUNL CbPZId75PgVF6hRNBAr3XiwFyiu6p++OiFjWFIXl2hri56vGBMQVfz4ALicIdbSvkvOB rn9A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=pAhRX1Y8hlT53IJmsS9eKDWXvMfY7PiqTbL9YMzPsQY=; b=U6mkni8gqVFHfKlIoZWtMJ1iHwJEXH1jXrn4noJCUyAJ/ofoVXn9sdoxr7716udtpy 0WK7daAhF/cCxH4oZReKIUAR+tIhfUELTCdwXdUcRh4Jm+lFM+EeH8r2nK6qIh+awyl8 r9hQx3gqG3aswc2oKfW+R4ejhUUW6VafVhfwA+nc8p48ZhmK5LO9+LxabcnqcgTUDjYz SLdc4Ls3Khiazclsb8keRJQIpMygF78gYEI9nyQpg8bO7TYZCJsLIMFLzydnIIe64nkD 2QKHq6Eh7UO1f+UOI2l7tZt+fBa/KXJ7F+bFjjY+sQisqoo5agSL8UH56dkS/tmNE21w Wi+Q== X-Gm-Message-State: APjAAAXxEZG2oFiMt9umDZsIFYrR0n34kB6e759gYRE9P0EZCd/zaSbe IdqESy/w/m/vJqKW0znmcOOROgXCy6RQ03vmhVY= X-Google-Smtp-Source: APXvYqzVVj6XLIRKAQFw0YAZbGXg8avRlJ7jD1nt0GvxOdj6vD309EupfSe3MyuCDlpLhg5U72LmlbjcnSDQAz+lgp4= X-Received: by 2002:a9d:aa8:: with SMTP id 37mr1771178otq.56.1568708580413; Tue, 17 Sep 2019 01:23:00 -0700 (PDT) MIME-Version: 1.0 References: <1568617969-6934-1-git-send-email-wanpengli@tencent.com> <20190916191218.GM18871@linux.intel.com> In-Reply-To: <20190916191218.GM18871@linux.intel.com> From: Wanpeng Li Date: Tue, 17 Sep 2019 16:22:48 +0800 Message-ID: Subject: Re: [PATCH] KVM: X86: Fix warning in handle_desc To: Sean Christopherson Cc: LKML , kvm , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , "# v3 . 10+" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 17 Sep 2019 at 03:12, Sean Christopherson wrote: > > 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()? I'm a little lazy, just extract CPUID and CR4 combination checking and add it to __set_sregs() in new version. Wanpeng