svsm: validate memory correctly during kernel region expansion

By the time the kernel region is expanded, the memory to be used for the
heap has already been validated.  Therefore, as the kernel region is
expanded, newly added memory must be validated as it is added, and there
is no reason to validate new page table pages as they are allocated from
existing heap space.

Signed-off-by: Jon Lange <jlange@microsoft.com>

Author: msft-jlange

kernel/src/kernel_region.rs

@@ -121,20 +121,6 @@ pub unsafe fn expand_kernel_heap(
                 let new_pdpe_vaddr = VirtAddr::from(u64::from(new_pdpe_paddr) + phys_virt_diff);
                 allocated_pages += 1;
 
-                // Prior to full heap initialization, unallocated heap pages
-                // are not validated.  Since this page is now allocated, it
-                // must be validated before it can be used.
-                // SAFETY: the newly mapped page is being used for the first
-                // time, so it can be validated safely.
-                unsafe {
-                    platform
-                        .validate_virtual_page_range(
-                            MemoryRegion::new(new_pdpe_vaddr, PAGE_SIZE),
-                            PageValidateOp::Validate,
-                        )
-                        .expect("Failed to validate heap memory");
-                }
-
                 // Ensure that the newly allocated page is filled with zeroes.
                 // SAFETY: the newly allocated page is known to be unused
                 // because it is outside the bounds of allocated hep pages, and
@@ -156,6 +142,20 @@ pub unsafe fn expand_kernel_heap(
         // Fill in the PDE for the next direct map address in sequence.
         pdt[pde_index].set(make_private_address(paddr), pte_flags);
 
+        // By the time kernel region expansion is performed, the heap area has
+        // been fully validated.  Now that a new large page has been added,
+        // that memory must be validated as well.
+        // SAFETY: the newly mapped page is being used for the first
+        // time, so it can be validated safely.
+        unsafe {
+            platform
+                .validate_virtual_page_range(
+                    MemoryRegion::new(vaddr, PAGE_SIZE_2M),
+                    PageValidateOp::Validate,
+                )
+                .expect("Failed to validate heap memory");
+        }
+
         paddr = paddr + PAGE_SIZE_2M;
         vaddr = vaddr + PAGE_SIZE_2M;
         expansion_size -= PAGE_SIZE_2M as u64;