KVM: x86: Add capability to grant VM access to privileged SGX attribute

mainline inclusion
from mainline-5.13
commit fe7e9488
category: feature
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I5EZEK
CVE: NA

Intel-SIG: commit fe7e9488 KVM: x86: Add capability to grant VM
access to privileged SGX attribute.
Backport for SGX virtualization support

--------------------------------

Add a capability, KVM_CAP_SGX_ATTRIBUTE, that can be used by userspace
to grant a VM access to a priveleged attribute, with args[0] holding a
file handle to a valid SGX attribute file.

The SGX subsystem restricts access to a subset of enclave attributes to
provide additional security for an uncompromised kernel, e.g. to prevent
malware from using the PROVISIONKEY to ensure its nodes are running
inside a geniune SGX enclave and/or to obtain a stable fingerprint.

To prevent userspace from circumventing such restrictions by running an
enclave in a VM, KVM restricts guest access to privileged attributes by
default.

Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: NSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: NKai Huang <kai.huang@intel.com>
Message-Id: <0b099d65e933e068e3ea934b0523bab070cb8cea.1618196135.git.kai.huang@intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NFan Du <fan.du@intel.com>
Signed-off-by: NZhiquan Li <zhiquan1.li@intel.com>

Documentation/virt/kvm/api.rst

@@ -6197,6 +6197,29 @@ KVM_EXIT_X86_RDMSR and KVM_EXIT_X86_WRMSR exit notifications which user space
 can then handle to implement model specific MSR handling and/or user notifications
 to inform a user that an MSR was not handled.
 
+7.25 KVM_CAP_SGX_ATTRIBUTE
+----------------------
+
+:Architectures: x86
+:Target: VM
+:Parameters: args[0] is a file handle of a SGX attribute file in securityfs
+:Returns: 0 on success, -EINVAL if the file handle is invalid or if a requested
+          attribute is not supported by KVM.
+
+KVM_CAP_SGX_ATTRIBUTE enables a userspace VMM to grant a VM access to one or
+more priveleged enclave attributes.  args[0] must hold a file handle to a valid
+SGX attribute file corresponding to an attribute that is supported/restricted
+by KVM (currently only PROVISIONKEY).
+
+The SGX subsystem restricts access to a subset of enclave attributes to provide
+additional security for an uncompromised kernel, e.g. use of the PROVISIONKEY
+is restricted to deter malware from using the PROVISIONKEY to obtain a stable
+system fingerprint.  To prevent userspace from circumventing such restrictions
+by running an enclave in a VM, KVM prevents access to privileged attributes by
+default.
+
+See Documentation/x86/sgx/2.Kernel-internals.rst for more details.
+
 8. Other capabilities.
 ======================
 

arch/x86/kvm/cpuid.c

@@ -834,7 +834,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		 * expected to derive it from supported XCR0.
 		 */
 		entry->eax &= SGX_ATTR_DEBUG | SGX_ATTR_MODE64BIT |
-			      /* PROVISIONKEY | */ SGX_ATTR_EINITTOKENKEY |
+			      SGX_ATTR_PROVISIONKEY | SGX_ATTR_EINITTOKENKEY |
 			      SGX_ATTR_KSS;
 		entry->ebx &= 0;
 		break;

arch/x86/kvm/x86.c

@@ -74,6 +74,7 @@
 #include <asm/tlbflush.h>
 #include <asm/intel_pt.h>
 #include <asm/emulate_prefix.h>
+#include <asm/sgx.h>
 #include <clocksource/hyperv_timer.h>
 
 #define CREATE_TRACE_POINTS
@@ -3842,6 +3843,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_X86_USER_SPACE_MSR:
 	case KVM_CAP_X86_MSR_FILTER:
 	case KVM_CAP_ENFORCE_PV_FEATURE_CPUID:
+#ifdef CONFIG_X86_SGX_KVM
+	case KVM_CAP_SGX_ATTRIBUTE:
+#endif
 		r = 1;
 		break;
 	case KVM_CAP_SYNC_REGS:
@@ -5394,6 +5398,23 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		kvm->arch.user_space_msr_mask = cap->args[0];
 		r = 0;
 		break;
+#ifdef CONFIG_X86_SGX_KVM
+	case KVM_CAP_SGX_ATTRIBUTE: {
+		unsigned long allowed_attributes = 0;
+
+		r = sgx_set_attribute(&allowed_attributes, cap->args[0]);
+		if (r)
+			break;
+
+		/* KVM only supports the PROVISIONKEY privileged attribute. */
+		if ((allowed_attributes & SGX_ATTR_PROVISIONKEY) &&
+		    !(allowed_attributes & ~SGX_ATTR_PROVISIONKEY))
+			kvm->arch.sgx_provisioning_allowed = true;
+		else
+			r = -EINVAL;
+		break;
+	}
+#endif
 	default:
 		r = -EINVAL;
 		break;

include/uapi/linux/kvm.h

@@ -1061,6 +1061,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_X86_USER_SPACE_MSR 188
 #define KVM_CAP_X86_MSR_FILTER 189
 #define KVM_CAP_ENFORCE_PV_FEATURE_CPUID 190
+#define KVM_CAP_SGX_ATTRIBUTE 196
 
 #define KVM_CAP_ARM_CPU_FEATURE 555