pe: Fix PF in GRUB after memattrs call

The call to update_mem_attrs() takes an aligned pointer within an
allocated region but passes the entire size of the allocated region. The
result is that Shim may remove execute permission from some pages
belonging to GRUB causing a page fault upon returning from the LoadImage
call.

There are two cases:
* When loading the image, set the memory attributes for exactly what we
  intend to load.
* When freeing the image, be cautious and apply the edk2 workaround for
  the entire allocated region.

Fixes: 226fee2 ("PE Loader: support and require NX")
Fixes: 2f64bb9 ("loader-protocol: add workaround for EDK2 2025.02 page fault on FreePages")
Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>

Author: rosslagerwall

loader-proto.c

@@ -186,8 +186,6 @@ try_load_from_lf2(EFI_DEVICE_PATH *dp, buffer_properties_t *bprop)
 static void
 free_pages_alloc_image(SHIM_LOADED_IMAGE *image)
 {
-	char *buffer;
-
 	if (!image || !image->alloc_address || !image->alloc_pages)
 		return;
 
@@ -196,9 +194,8 @@ free_pages_alloc_image(SHIM_LOADED_IMAGE *image)
 	 * are set on a loaded image, this will cause a page fault when it
 	 * is freed. Ensure W+ X- are set instead before freeing. */
 
-	buffer = (void *)ALIGN_VALUE((unsigned long)image->alloc_address, image->alloc_alignment);
-	update_mem_attrs((uintptr_t)buffer, image->alloc_pages * PAGE_SIZE, MEM_ATTR_R|MEM_ATTR_W,
-			 MEM_ATTR_X);
+	update_mem_attrs((uintptr_t)image->alloc_address,
+			 image->alloc_pages * PAGE_SIZE, MEM_ATTR_R|MEM_ATTR_W, MEM_ATTR_X);
 
 	BS->FreePages(image->alloc_address, image->alloc_pages);
 	image->alloc_address = 0;

pe.c

@@ -717,7 +717,7 @@ handle_image (void *data, unsigned int datasize,
 	dprint(L"Loading 0x%llx bytes at 0x%llx\n",
 	       (unsigned long long)context.ImageSize,
 	       (unsigned long long)(uintptr_t)buffer);
-	update_mem_attrs((uintptr_t)buffer, alloc_size, MEM_ATTR_R|MEM_ATTR_W,
+	update_mem_attrs((uintptr_t)buffer, context.ImageSize, MEM_ATTR_R|MEM_ATTR_W,
 			 MEM_ATTR_X);
 
 	CopyMem(buffer, data, context.SizeOfHeaders);