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

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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>
This commit is contained in:
Sean Christopherson 2021-04-12 16:21:43 +12:00 committed by Paolo Bonzini
parent 72add915fb
commit fe7e948837
4 changed files with 46 additions and 1 deletions
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23
Documentation/virt/kvm/api.rst
View File

@ -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.
======================

2
arch/x86/kvm/cpuid.c
View File

@ -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;

21
arch/x86/kvm/x86.c
View File

@ -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;

1
include/uapi/linux/kvm.h
View File

@ -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