From patchwork Mon Jan 18 03:28:31 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kai Huang X-Patchwork-Id: 12026393 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 187D8C433E6 for ; Mon, 18 Jan 2021 03:30:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DF06D224B1 for ; Mon, 18 Jan 2021 03:30:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731726AbhARDaY (ORCPT ); Sun, 17 Jan 2021 22:30:24 -0500 Received: from mga12.intel.com ([192.55.52.136]:16949 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731738AbhARDaA (ORCPT ); Sun, 17 Jan 2021 22:30:00 -0500 IronPort-SDR: sqRkIMu2teHXpUUWcUf4kp50Tel6RCOuoFojEU7PP61V1atTyaDfhMGtDOzZ2VJ5E1TyeIRkGS DrXXWJ0toSRg== X-IronPort-AV: E=McAfee;i="6000,8403,9867"; a="157933915" X-IronPort-AV: E=Sophos;i="5.79,355,1602572400"; d="scan'208";a="157933915" Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Jan 2021 19:29:11 -0800 IronPort-SDR: sN05114G+PrKV795Fsti/+ffQlHDBPd3dtzd3LIxRPUXRBgX05HCvJVutBbM2d08gU8Xg3Ccif Vizxa8U6drkQ== X-IronPort-AV: E=Sophos;i="5.79,355,1602572400"; d="scan'208";a="573151140" Received: from amrahman-mobl.amr.corp.intel.com (HELO khuang2-desk.gar.corp.intel.com) ([10.252.142.253]) by fmsmga005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Jan 2021 19:29:07 -0800 From: Kai Huang To: linux-sgx@vger.kernel.org, kvm@vger.kernel.org, x86@kernel.org Cc: seanjc@google.com, jarkko@kernel.org, luto@kernel.org, dave.hansen@intel.com, haitao.huang@intel.com, pbonzini@redhat.com, bp@alien8.de, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, jmattson@google.com, joro@8bytes.org, vkuznets@redhat.com, wanpengli@tencent.com, Kai Huang Subject: [RFC PATCH v2 20/26] KVM: VMX: Add basic handling of VM-Exit from SGX enclave Date: Mon, 18 Jan 2021 16:28:31 +1300 Message-Id: X-Mailer: git-send-email 2.29.2 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org From: Sean Christopherson Add support for handling VM-Exits that originate from a guest SGX enclave. In SGX, an "enclave" is a new CPL3-only execution environment, wherein the CPU and memory state is protected by hardware to make the state inaccesible to code running outside of the enclave. When exiting an enclave due to an asynchronous event (from the perspective of the enclave), e.g. exceptions, interrupts, and VM-Exits, the enclave's state is automatically saved and scrubbed (the CPU loads synthetic state), and then reloaded when re-entering the enclave. E.g. after an instruction based VM-Exit from an enclave, vmcs.GUEST_RIP will not contain the RIP of the enclave instruction that trigered VM-Exit, but will instead point to a RIP in the enclave's untrusted runtime (the guest userspace code that coordinates entry/exit to/from the enclave). To help a VMM recognize and handle exits from enclaves, SGX adds bits to existing VMCS fields, VM_EXIT_REASON.VMX_EXIT_REASON_FROM_ENCLAVE and GUEST_INTERRUPTIBILITY_INFO.GUEST_INTR_STATE_ENCLAVE_INTR. Define the new architectural bits, and add a boolean to struct vcpu_vmx to cache VMX_EXIT_REASON_FROM_ENCLAVE. Clear the bit in exit_reason so that checks against exit_reason do not need to account for SGX, e.g. "if (exit_reason == EXIT_REASON_EXCEPTION_NMI)" continues to work. KVM is a largely a passive observer of the new bits, e.g. KVM needs to account for the bits when propagating information to a nested VMM, but otherwise doesn't need to act differently for the majority of VM-Exits from enclaves. The one scenario that is directly impacted is emulation, which is for all intents and purposes impossible[1] since KVM does not have access to the RIP or instruction stream that triggered the VM-Exit. The inability to emulate is a non-issue for KVM, as most instructions that might trigger VM-Exit unconditionally #UD in an enclave (before the VM-Exit check. For the few instruction that conditionally #UD, KVM either never sets the exiting control, e.g. PAUSE_EXITING[2], or sets it if and only if the feature is not exposed to the guest in order to inject a #UD, e.g. RDRAND_EXITING. But, because it is still possible for a guest to trigger emulation, e.g. MMIO, inject a #UD if KVM ever attempts emulation after a VM-Exit from an enclave. This is architecturally accurate for instruction VM-Exits, and for MMIO it's the least bad choice, e.g. it's preferable to killing the VM. In practice, only broken or particularly stupid guests should ever encounter this behavior. Add a WARN in skip_emulated_instruction to detect any attempt to modify the guest's RIP during an SGX enclave VM-Exit as all such flows should either be unreachable or must handle exits from enclaves before getting to skip_emulated_instruction. [1] Impossible for all practical purposes. Not truly impossible since KVM could implement some form of para-virtualization scheme. [2] PAUSE_LOOP_EXITING only affects CPL0 and enclaves exist only at CPL3, so we also don't need to worry about that interaction. Signed-off-by: Sean Christopherson [Kai: Remove unlikely()s suggested by Dave Hansen.] Signed-off-by: Kai Huang --- arch/x86/include/asm/vmx.h | 1 + arch/x86/include/uapi/asm/vmx.h | 1 + arch/x86/kvm/vmx/nested.c | 2 ++ arch/x86/kvm/vmx/vmx.c | 38 +++++++++++++++++++++++++++++++-- 4 files changed, 40 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h index 38ca445a8429..e99021a00eb9 100644 --- a/arch/x86/include/asm/vmx.h +++ b/arch/x86/include/asm/vmx.h @@ -372,6 +372,7 @@ enum vmcs_field { #define GUEST_INTR_STATE_MOV_SS 0x00000002 #define GUEST_INTR_STATE_SMI 0x00000004 #define GUEST_INTR_STATE_NMI 0x00000008 +#define GUEST_INTR_STATE_ENCLAVE_INTR 0x00000010 /* GUEST_ACTIVITY_STATE flags */ #define GUEST_ACTIVITY_ACTIVE 0 diff --git a/arch/x86/include/uapi/asm/vmx.h b/arch/x86/include/uapi/asm/vmx.h index ada955c5ebb6..c7a18eb2a074 100644 --- a/arch/x86/include/uapi/asm/vmx.h +++ b/arch/x86/include/uapi/asm/vmx.h @@ -27,6 +27,7 @@ #define VMX_EXIT_REASONS_FAILED_VMENTRY 0x80000000 +#define VMX_EXIT_REASONS_SGX_ENCLAVE_MODE 0x08000000 #define EXIT_REASON_EXCEPTION_NMI 0 #define EXIT_REASON_EXTERNAL_INTERRUPT 1 diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index f112c2482887..562eab7b0a51 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -4126,6 +4126,8 @@ static void prepare_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12, { /* update exit information fields: */ vmcs12->vm_exit_reason = vm_exit_reason; + if (to_vmx(vcpu)->exit_reason.sgx_enclave_mode) + vmcs12->vm_exit_reason |= VMX_EXIT_REASONS_SGX_ENCLAVE_MODE; vmcs12->exit_qualification = exit_qualification; vmcs12->vm_exit_intr_info = exit_intr_info; diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 746b87375aff..4cb8a3f1374c 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -1561,12 +1561,18 @@ static int vmx_rtit_ctl_check(struct kvm_vcpu *vcpu, u64 data) static bool vmx_can_emulate_instruction(struct kvm_vcpu *vcpu, void *insn, int insn_len) { + if (to_vmx(vcpu)->exit_reason.sgx_enclave_mode) { + kvm_queue_exception(vcpu, UD_VECTOR); + return false; + } return true; } static int skip_emulated_instruction(struct kvm_vcpu *vcpu) { + union vmx_exit_reason exit_reason = to_vmx(vcpu)->exit_reason; unsigned long rip, orig_rip; + u32 instr_len; /* * Using VMCS.VM_EXIT_INSTRUCTION_LEN on EPT misconfig depends on @@ -1577,9 +1583,33 @@ static int skip_emulated_instruction(struct kvm_vcpu *vcpu) * i.e. we end up advancing IP with some random value. */ if (!static_cpu_has(X86_FEATURE_HYPERVISOR) || - to_vmx(vcpu)->exit_reason.basic != EXIT_REASON_EPT_MISCONFIG) { + exit_reason.basic != EXIT_REASON_EPT_MISCONFIG) { + instr_len = vmcs_read32(VM_EXIT_INSTRUCTION_LEN); + + /* + * Emulating an enclave's instructions isn't supported as KVM + * cannot access the enclave's memory or its true RIP, e.g. the + * vmcs.GUEST_RIP points at the exit point of the enclave, not + * the RIP that actually triggered the VM-Exit. But, because + * most instructions that cause VM-Exit will #UD in an enclave, + * most instruction-based VM-Exits simply do not occur. + * + * There are a few exceptions, notably the debug instructions + * INT1ICEBRK and INT3, as they are allowed in debug enclaves + * and generate #DB/#BP as expected, which KVM might intercept. + * But again, the CPU does the dirty work and saves an instr + * length of zero so VMMs don't shoot themselves in the foot. + * WARN if KVM tries to skip a non-zero length instruction on + * a VM-Exit from an enclave. + */ + if (!instr_len) + goto rip_updated; + + WARN(exit_reason.sgx_enclave_mode, + "KVM: skipping instruction after SGX enclave VM-Exit"); + orig_rip = kvm_rip_read(vcpu); - rip = orig_rip + vmcs_read32(VM_EXIT_INSTRUCTION_LEN); + rip = orig_rip + instr_len; #ifdef CONFIG_X86_64 /* * We need to mask out the high 32 bits of RIP if not in 64-bit @@ -1595,6 +1625,7 @@ static int skip_emulated_instruction(struct kvm_vcpu *vcpu) return 0; } +rip_updated: /* skipping an emulated instruction also counts */ vmx_set_interrupt_shadow(vcpu, 0); @@ -5341,6 +5372,9 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu) { gpa_t gpa; + if (!vmx_can_emulate_instruction(vcpu, NULL, 0)) + return 1; + /* * A nested guest cannot optimize MMIO vmexits, because we have an * nGPA here instead of the required GPA.