[RFC PATCH v1 24/42] KVM: planes: expose memory-attribute setting to in-kernel callers

[Sriram Nambakam <snambakam@linux.microsoft.com>]

A higher-privilege plane needs to restrict a lower plane's access to
guest memory by setting NO_WRITE / NO_EXEC EPT attributes (e.g. HEKI
sealing plane-0 text/rodata). The enforcement already lives in
kvm_plane_filter_pte_access(); wire up the set side:

 - advertise KVM_MEMORY_ATTRIBUTE_NO_WRITE / NO_EXEC from
   kvm_supported_mem_attributes() when CONFIG_VM_PLANES is enabled, so
   userspace and in-kernel callers know the attributes are available.

 - make kvm_vm_set_mem_attributes() non-static and declare it in
   kvm_host.h so an in-kernel secure-plane caller can apply attributes
   without going through the ioctl path.

No functional change for non-plane builds.

Signed-off-by: Sriram Nambakam <snambakam@linux.microsoft.com>
---
 include/linux/kvm_host.h |  2 ++
 virt/kvm/kvm_main.c      | 21 +++++++++++++++++----
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index e989b293a34a..82e557e66152 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2703,6 +2703,8 @@ static inline unsigned long kvm_get_memory_attributes(struct kvm *kvm, gfn_t gfn
 
 bool kvm_range_has_memory_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
 				     unsigned long mask, unsigned long attrs);
+int kvm_vm_set_mem_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
+			      unsigned long attributes);
 bool kvm_arch_pre_set_memory_attributes(struct kvm *kvm,
 					struct kvm_gfn_range *range);
 bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f703545a7e80..9623ab8ebd9e 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2603,10 +2603,23 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
 #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
 static u64 kvm_supported_mem_attributes(struct kvm *kvm)
 {
+	u64 attrs = 0;
+
 	if (!kvm || kvm_arch_has_private_mem(kvm))
-		return KVM_MEMORY_ATTRIBUTE_PRIVATE;
+		attrs |= KVM_MEMORY_ATTRIBUTE_PRIVATE;
 
-	return 0;
+#ifdef CONFIG_VM_PLANES
+	/*
+	 * Cross-plane EPT protection: a higher-privilege plane may restrict
+	 * a lower plane's access via NO_WRITE / NO_EXEC (e.g. HEKI sealing
+	 * plane-0 kernel text and rodata).  The enforcement path lives in
+	 * kvm_plane_filter_pte_access(); advertise the attributes here so
+	 * KVM_SET_MEMORY_ATTRIBUTES accepts them.
+	 */
+	attrs |= KVM_MEMORY_ATTRIBUTE_NO_WRITE | KVM_MEMORY_ATTRIBUTE_NO_EXEC;
+#endif
+
+	return attrs;
 }
 
 /*
@@ -2716,8 +2729,8 @@ static bool kvm_pre_set_memory_attributes(struct kvm *kvm,
 }
 
 /* Set @attributes for the gfn range [@start, @end). */
-static int kvm_vm_set_mem_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
-				     unsigned long attributes)
+int kvm_vm_set_mem_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
+			      unsigned long attributes)
 {
 	struct kvm_mmu_notifier_range pre_set_range = {
 		.start = start,
-- 
2.55.0