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Tue, 15 Sep 2020 13:37:15 +0000 Subject: Re: [RFC PATCH 08/35] KVM: SVM: Prevent debugging under SEV-ES To: Sean Christopherson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, Paolo Bonzini , Jim Mattson , Joerg Roedel , Vitaly Kuznetsov , Wanpeng Li , Borislav Petkov , Ingo Molnar , Thomas Gleixner , Brijesh Singh References: <58093c542b5b442b88941828595fb2548706f1bf.1600114548.git.thomas.lendacky@amd.com> <20200914212601.GA7192@sjchrist-ice> From: Tom Lendacky Message-ID: Date: Tue, 15 Sep 2020 08:37:12 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 In-Reply-To: <20200914212601.GA7192@sjchrist-ice> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: DM5PR1101CA0014.namprd11.prod.outlook.com (2603:10b6:4:4c::24) To CY4PR12MB1352.namprd12.prod.outlook.com (2603:10b6:903:3a::13) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [10.236.30.118] (165.204.77.1) by DM5PR1101CA0014.namprd11.prod.outlook.com (2603:10b6:4:4c::24) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3370.16 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: 80bfdd24-a4dd-4e39-0c97-08d8597c7547 X-MS-Exchange-CrossTenant-AuthSource: CY4PR12MB1352.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Sep 2020 13:37:15.4231 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: FxmxwrQ+e1KmPs2FnWKOgs+lSpimWXT/rlReGx/3frvEFhq1a+tNHlFNFIS7SKkDyIMMoZb3mIzJMK87lkd+eA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR12MB1926 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/14/20 4:26 PM, Sean Christopherson wrote: > On Mon, Sep 14, 2020 at 03:15:22PM -0500, Tom Lendacky wrote: >> From: Tom Lendacky >> >> Since the guest register state of an SEV-ES guest is encrypted, debugging >> is not supported. Update the code to prevent guest debugging when the >> guest is an SEV-ES guest. This includes adding a callable function that >> is used to determine if the guest supports being debugged. >> >> Signed-off-by: Tom Lendacky >> --- >> arch/x86/include/asm/kvm_host.h | 2 ++ >> arch/x86/kvm/svm/svm.c | 16 ++++++++++++++++ >> arch/x86/kvm/vmx/vmx.c | 7 +++++++ >> arch/x86/kvm/x86.c | 3 +++ >> 4 files changed, 28 insertions(+) >> >> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h >> index c900992701d6..3e2a3d2a8ba8 100644 >> --- a/arch/x86/include/asm/kvm_host.h >> +++ b/arch/x86/include/asm/kvm_host.h >> @@ -1234,6 +1234,8 @@ struct kvm_x86_ops { >> void (*reg_read_override)(struct kvm_vcpu *vcpu, enum kvm_reg reg); >> void (*reg_write_override)(struct kvm_vcpu *vcpu, enum kvm_reg reg, >> unsigned long val); >> + >> + bool (*allow_debug)(struct kvm *kvm); > > Why add both allow_debug() and vmsa_encrypted? I assume there are scenarios > where allow_debug() != vmsa_encrypted? E.g. is there a debug mode for SEV-ES > where the VMSA is not encrypted, but KVM (ironically) can't intercept #DBs or > something? No, once the guest has had LAUNCH_UPDATE_VMSA run against the vCPUs, then the vCPU states are all encrypted. But that doesn't mean that debugging can't be done in the future. > > Alternatively, have you explored using a new VM_TYPE for SEV-ES guests? With > a genericized vmsa_encrypted, that would allow something like the following > for scenarios where the VMSA is not (yet?) encrypted for an SEV-ES guest. I > don't love bleeding the VM type into x86.c, but for one-off quirks like this > I think it'd be preferable to adding a kvm_x86_ops hook. > > int kvm_arch_vcpu_ioctl_set_guest_debug(...) > { > if (vcpu->arch.guest_state_protected || > kvm->arch.vm_type == KVM_X86_SEV_ES_VM) > return -EINVAL; > } > I haven't explored that, I'll look into it. Thanks, Tom