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

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: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Kai Huang <kai.huang@intel.com>
Message-Id: <0b099d65e933e068e3ea934b0523bab070cb8cea.1618196135.git.kai.huang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 1b94cce..414b7fe 100644 (file)
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6207,6 +6207,29 @@ KVM_RUN_BUS_LOCK flag is used to distinguish between them.
 This capability can be used to check / enable 2nd DAWR feature provided
 by POWER10 processor.
 
+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.
 ======================
 

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 29365c1..2ae0615 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -849,7 +849,7 @@ 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;

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d4063be..d4cdab1 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -75,6 +75,7 @@
 #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
@@ -3804,6 +3805,9 @@ 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_SET_GUEST_DEBUG2:
@@ -5392,6 +5396,23 @@ split_irqchip_unlock:
                        kvm->arch.bus_lock_detection_enabled = true;
                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;

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 7270107..162b7e0 100644 (file)
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1079,6 +1079,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_X86_BUS_LOCK_EXIT 193
 #define KVM_CAP_PPC_DAWR1 194
 #define KVM_CAP_SET_GUEST_DEBUG2 195
+#define KVM_CAP_SGX_ATTRIBUTE 196
 
 #ifdef KVM_CAP_IRQ_ROUTING