Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753019Ab3IIOJr (ORCPT ); Mon, 9 Sep 2013 10:09:47 -0400 Received: from mail-qa0-f44.google.com ([209.85.216.44]:62980 "EHLO mail-qa0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751495Ab3IIOJp (ORCPT ); Mon, 9 Sep 2013 10:09:45 -0400 Message-ID: <522DD6AB.1030303@redhat.com> Date: Mon, 09 Sep 2013 16:09:47 +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, kvm@vger.kernel.org Subject: Re: [PATCH] KVM: x86: prevent setting unsupported XSAVE states References: <1378383714-9723-2-git-send-email-pbonzini@redhat.com> <20130908095446.GE17294@redhat.com> In-Reply-To: <20130908095446.GE17294@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: 3883 Lines: 110 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). Paolo >> 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, >> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h >> index e224f7a..587fb9e 100644 >> --- a/arch/x86/kvm/x86.h >> +++ b/arch/x86/kvm/x86.h >> @@ -122,6 +122,7 @@ int kvm_write_guest_virt_system(struct x86_emulate_ctxt *ctxt, >> gva_t addr, void *val, unsigned int bytes, >> struct x86_exception *exception); >> >> +#define KVM_SUPPORTED_XCR0 (XSTATE_FP | XSTATE_SSE | XSTATE_YMM) >> extern u64 host_xcr0; >> >> extern struct static_key kvm_no_apic_vcpu; >> -- >> 1.8.3.1 > > -- > Gleb. > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- 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/