From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755531Ab3IIQ6K (ORCPT ); Mon, 9 Sep 2013 12:58:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36569 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755654Ab3IIQ56 (ORCPT ); Mon, 9 Sep 2013 12:57:58 -0400 Date: Mon, 9 Sep 2013 19:57:55 +0300 From: Gleb Natapov To: Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH] KVM: x86: prevent setting unsupported XSAVE states Message-ID: <20130909165755.GA4008@redhat.com> References: <1378383714-9723-2-git-send-email-pbonzini@redhat.com> <20130908095446.GE17294@redhat.com> <522DD6AB.1030303@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <522DD6AB.1030303@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 09, 2013 at 04:09:47PM +0200, Paolo Bonzini wrote: > Il 08/09/2013 11:54, Gleb Natapov ha scritto: > > On Thu, Sep 05, 2013 at 02:21:54PM +0200, Paolo Bonzini wrote: > >> A guest can still attempt to save and restore XSAVE states even if they > >> have been masked in CPUID leaf 0Dh. This usually is not visible to > >> the guest, but is still wrong: "Any attempt to set a reserved bit (as > >> determined by the contents of EAX and EDX after executing CPUID with > >> EAX=0DH, ECX= 0H) in XCR0 for a given processor will result in a #GP > >> exception". > >> > >> The patch also performs the same checks as __kvm_set_xcr in KVM_SET_XSAVE. > >> This catches migration from newer to older kernel/processor before the > >> guest starts running. > >> > >> Cc: kvm@vger.kernel.org > >> Cc: Gleb Natapov > >> Signed-off-by: Paolo Bonzini > >> --- > >> arch/x86/kvm/cpuid.c | 2 +- > >> arch/x86/kvm/x86.c | 10 ++++++++-- > >> arch/x86/kvm/x86.h | 1 + > >> 3 files changed, 10 insertions(+), 3 deletions(-) > >> > >> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > >> index a20ecb5..d7c465d 100644 > >> --- a/arch/x86/kvm/cpuid.c > >> +++ b/arch/x86/kvm/cpuid.c > >> @@ -182,7 +182,7 @@ static bool supported_xcr0_bit(unsigned bit) > >> { > >> u64 mask = ((u64)1 << bit); > >> > >> - return mask & (XSTATE_FP | XSTATE_SSE | XSTATE_YMM) & host_xcr0; > >> + return mask & KVM_SUPPORTED_XCR0 & host_xcr0; > >> } > >> > >> #define F(x) bit(X86_FEATURE_##x) > >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > >> index 3625798..801a882 100644 > >> --- a/arch/x86/kvm/x86.c > >> +++ b/arch/x86/kvm/x86.c > >> @@ -586,6 +586,8 @@ int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr) > >> return 1; > >> if ((xcr0 & XSTATE_YMM) && !(xcr0 & XSTATE_SSE)) > >> return 1; > >> + if (xcr0 & ~KVM_SUPPORTED_XCR0) > >> + return 1; > > Shouldn't we check guest's cpuid here? > > Yes. > > >> if (xcr0 & ~host_xcr0) > >> return 1; > >> kvm_put_guest_xcr0(vcpu); > >> @@ -2980,10 +2982,14 @@ static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu, > >> u64 xstate_bv = > >> *(u64 *)&guest_xsave->region[XSAVE_HDR_OFFSET / sizeof(u32)]; > >> > >> - if (cpu_has_xsave) > >> + if (cpu_has_xsave) { > >> + if (xstate_bv & ~KVM_SUPPORTED_XCR0) > >> + return -EINVAL; > >> + if (xstate_bv & ~host_xcr0) > >> + return -EINVAL; > > And here? > > Here it'd be nice, but we cannot due to backwards compatibility. We > agreed to change KVM_GET_XSAVE and make it only report states that are > included in CPUID, but we still need to do migration from old kernels > that report all states. > > If we change KVM_SET_XSAVE to look at CPUID, and the CPUID does not > include AVX, migration will fail from old kernel (KVM_GET_XSAVE reports > all states) to new kernel (KVM_SET_XSAVES checks against CPUID). > Yeah :( -- Gleb.