Ensure that the userspace actor attempting to disable NX hugepages has
permission to reboot the system. Since disabling NX hugepages would
allow a guest to crash the system, it is similar to reboot permissions.
This approach is the simplest permission gating, but passing a file
descriptor opened for write for the module parameter would also work
well and be more precise.
The latter approach was suggested by Sean Christopherson.
Suggested-by: Jim Mattson <jmattson@xxxxxxxxxx>
Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 2 ++
arch/x86/kvm/x86.c | 9 +++++++++
2 files changed, 11 insertions(+)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index b40c3113b14b..ca5674e04474 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -7850,6 +7850,8 @@ should adjust CPUID leaf 0xA to reflect that the PMU is disabled.
:Capability KVM_CAP_PMU_CAPABILITY
:Architectures: x86
:Type: vm
+:Returns 0 on success, -EPERM if the userspace process does not
+ have CAP_SYS_BOOT
This capability disables the NX huge pages mitigation for iTLB MULTIHIT.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e00dcf19f826..81e7d825639e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6063,6 +6063,15 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
mutex_unlock(&kvm->lock);
break;
case KVM_CAP_VM_DISABLE_NX_HUGE_PAGES:
+ /*
+ * Since the risk of disabling NX hugepages is a guest crashing
+ * the system, ensure the userspace process has permission to
+ * reboot the system.
+ */
+ if (!capable(CAP_SYS_BOOT)) {
+ r = -EPERM;
+ break;
+ }
kvm->arch.disable_nx_huge_pages = true;
kvm_update_nx_huge_pages(kvm);
r = 0;
--
2.35.1.1021.g381101b075-goog
