From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH 6/6] KVM: x86: check DR6/7 high-bits are clear only on long-mode Date: Mon, 16 Jun 2014 13:09:56 +0200 Message-ID: <539ED084.2000906@redhat.com> References: <1402837982-24959-1-git-send-email-namit@cs.technion.ac.il> <1402837982-24959-7-git-send-email-namit@cs.technion.ac.il> <539EC43F.607@redhat.com> <539EC7F7.2000208@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: gleb@kernel.org, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Nadav Amit , Nadav Amit Return-path: In-Reply-To: <539EC7F7.2000208@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org Il 16/06/2014 12:33, Nadav Amit ha scritto: >> >> Do you get this if the input register has bit 31 set? > No. To be frank, the scenario may be considered a bit synthetic: the > guest assigns a value to a general-purpose register in 64-bit mode, > setting the high 32-bits to some non-zero value. Then, later, in 32-bit > mode, the guest performs MOV DR instruction. In between the two > assignments, the general purpose register is unmodified, so the high > 32-bits of the general purpose registers are still set. > > Note that this scenario does not occur when MOV DR is emulated, but when > handle_dr() is called. In this case, the entire 64-bits of the general > purpose register used for MOV DR are read, regardless to the execution > mode of the guest. I wonder if the same bug happens elsewhere. For example, kvm_emulate_hypercall doesn't look at CS.L/CS.DB, which is really a corner case but arguably also a bug. kvm_hv_hypercall instead does it right. Perhaps we need a variant of kvm_register_read that (on 64-bit hosts) checks EFER/CS.L/CS.DB and masks the returned value accordingly. You could call it kvm_register_readl. Paolo