Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753729Ab3IWKWX (ORCPT ); Mon, 23 Sep 2013 06:22:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57779 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753419Ab3IWKWV (ORCPT ); Mon, 23 Sep 2013 06:22:21 -0400 Message-ID: <5240166D.5020401@redhat.com> Date: Mon, 23 Sep 2013 12:22:37 +0200 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130805 Thunderbird/17.0.8 MIME-Version: 1.0 To: Gleb Natapov CC: linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/3] KVM: x86: prevent setting unsupported XSAVE states References: <1379341591-6538-1-git-send-email-pbonzini@redhat.com> <1379341591-6538-3-git-send-email-pbonzini@redhat.com> <20130922093353.GI25202@redhat.com> In-Reply-To: <20130922093353.GI25202@redhat.com> X-Enigmail-Version: 1.5.2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4627 Lines: 138 Il 22/09/2013 11:33, Gleb Natapov ha scritto: > On Mon, Sep 16, 2013 at 04:26:30PM +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. >> >> Signed-off-by: Paolo Bonzini >> --- >> arch/x86/include/asm/kvm_host.h | 1 + >> arch/x86/kvm/cpuid.c | 7 +++++++ >> arch/x86/kvm/x86.c | 17 ++++++++++++++--- >> 3 files changed, 22 insertions(+), 3 deletions(-) >> >> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h >> index c76ff74..1553542 100644 >> --- a/arch/x86/include/asm/kvm_host.h >> +++ b/arch/x86/include/asm/kvm_host.h >> @@ -389,6 +389,7 @@ struct kvm_vcpu_arch { >> >> struct fpu guest_fpu; >> u64 xcr0; >> + u64 supported_xcr0; >> > Lets prefix it with guest_. Ok. >> struct kvm_pio_request pio; >> void *pio_data; >> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c >> index a03a9fa..fa754a8 100644 >> --- a/arch/x86/kvm/cpuid.c >> +++ b/arch/x86/kvm/cpuid.c >> @@ -46,6 +46,13 @@ void kvm_update_cpuid(struct kvm_vcpu *vcpu) >> apic->lapic_timer.timer_mode_mask = 1 << 17; >> } >> >> + best = kvm_find_cpuid_entry(vcpu, 0xD, 0); >> + if (!best) >> + return; > If QMEU will set AVX in 0xD and then remove cpuid leaf at all > supported_xcr0 will still have it. Right. Will fix. >> + vcpu->arch.supported_xcr0 = >> + (best->eax | ((u64)best->edx << 32)) & >> + host_xcr0 & KVM_SUPPORTED_XCR0; >> + >> kvm_pmu_cpuid_update(vcpu); >> } >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index e5ca72a..cc8c403 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -586,7 +586,7 @@ 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 & ~host_xcr0) >> + if (xcr0 & ~vcpu->arch.supported_xcr0) >> return 1; >> kvm_put_guest_xcr0(vcpu); >> vcpu->arch.xcr0 = xcr0; >> @@ -3003,10 +3003,19 @@ 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) { >> + /* >> + * Here we allow setting states that are not present in >> + * CPUID leaf 0xD, index 0, EDX:EAX. This is for compatibility >> + * with old userspace. >> + */ >> + if (xstate_bv & ~KVM_SUPPORTED_XCR0) >> + return -EINVAL; >> + if (xstate_bv & ~host_xcr0) >> + return -EINVAL; >> memcpy(&vcpu->arch.guest_fpu.state->xsave, >> guest_xsave->region, xstate_size); >> - else { >> + } else { >> if (xstate_bv & ~XSTATE_FPSSE) >> return -EINVAL; >> memcpy(&vcpu->arch.guest_fpu.state->fxsave, >> @@ -6940,6 +6948,9 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu) >> >> vcpu->arch.ia32_tsc_adjust_msr = 0x0; >> vcpu->arch.pv_time_enabled = false; >> + >> + vcpu->arch.supported_xcr0 = XSTATE_FPSSE; >> + > Why is this needed? It will make make __kvm_set_xcr() succeed if attempt > is made to set SSE bit when it is not supported in cpuid. This may not > be an issue in practice, but for clarity it is better for supported_xcr0 > to contain only what is supported in guest's cpuid bits and handle the > fact that FP/SSE state should always be copied to/from userspace in > kvm_vcpu_ioctl_x86_(set|get)_xsave functions. I don't think it makes sense to disable SSE but not XSAVE. Linux even has this: if ((pcntxt_mask & XSTATE_FPSSE) != XSTATE_FPSSE) { pr_err("FP/SSE not shown under xsave features 0x%llx\n", pcntxt_mask); BUG(); } I preferred this to adding dubiously-testable code that probed CPUID for SSE support (or should I check FXSR instead?) Paolo >> kvm_async_pf_hash_reset(vcpu); >> kvm_pmu_init(vcpu); >> >> -- >> 1.8.3.1 >> > > -- > Gleb. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/