Restore loaded image of shim at Exit()

When grub2 invoked Exit() in AArch64 AAVMF, the VM crashed with the
following messsages:

Unloading driver at 0x000B7D7B000

Synchronous Exception at 0x00000000BF5D5E68
AllocatePool: failed to allocate 800 bytes

Synchronous Exception at 0x00000000BF5D5E68

The similar error also showed when I modified MokManager to call
gBS->Exit() at the end of efi_main(). However, if MokManager just
returned, the error never showed. One significant difference is
whether the loaded image was restored or not, and the firmware seems
to need the original ImageBase pointer to do clean-up.

To avoid the potential crash, this commit adds restore_loaded_image() so
that we can restore the loaded image both in start_image() and
do_exit().

Signed-off-by: Gary Lin <glin@suse.com>

1 files changed, 24 insertions, 17 deletions

diff --git a/shim.c b/shim.c
index 765c9254..32bc3e81 100644
--- a/shim.c
+++ b/shim.c
@@ -38,6 +38,8 @@
 
 static EFI_SYSTEM_TABLE *systab;
 static EFI_HANDLE global_image_handle;
+static EFI_LOADED_IMAGE *shim_li;
+static EFI_LOADED_IMAGE shim_li_bak;
 
 static CHAR16 *second_stage;
 void *load_options;
@@ -1069,13 +1071,24 @@ static EFI_STATUS shim_read_header(void *data, unsigned int datasize,
 	return efi_status;
 }
 
+VOID
+restore_loaded_image(VOID)
+{
+	if (shim_li->FilePath)
+		FreePool(shim_li->FilePath);
+
+	/*
+	 * Restore our original loaded image values
+	 */
+	CopyMem(shim_li, &shim_li_bak, sizeof(shim_li_bak));
+}
+
 /*
  * Load and run an EFI executable
  */
 EFI_STATUS start_image(EFI_HANDLE image_handle, CHAR16 *ImagePath)
 {
 	EFI_STATUS efi_status;
-	EFI_LOADED_IMAGE *li, li_bak;
 	EFI_IMAGE_ENTRY_POINT entry_point;
 	EFI_PHYSICAL_ADDRESS alloc_address;
 	UINTN alloc_pages;
@@ -1090,7 +1103,7 @@ EFI_STATUS start_image(EFI_HANDLE image_handle, CHAR16 *ImagePath)
 	 * binary in order to find our path
 	 */
 	efi_status = gBS->HandleProtocol(image_handle, &EFI_LOADED_IMAGE_GUID,
-					 (void **)&li);
+					 (void **)&shim_li);
 	if (EFI_ERROR(efi_status)) {
 		perror(L"Unable to init protocol\n");
 		return efi_status;
@@ -1099,14 +1112,14 @@ EFI_STATUS start_image(EFI_HANDLE image_handle, CHAR16 *ImagePath)
 	/*
 	 * Build a new path from the existing one plus the executable name
 	 */
-	efi_status = generate_path_from_image_path(li, ImagePath, &PathName);
+	efi_status = generate_path_from_image_path(shim_li, ImagePath, &PathName);
 	if (EFI_ERROR(efi_status)) {
 		perror(L"Unable to generate path %s: %r\n", ImagePath,
 		       efi_status);
 		goto done;
 	}
 
-	if (findNetboot(li->DeviceHandle)) {
+	if (findNetboot(shim_li->DeviceHandle)) {
 		efi_status = parseNetbootinfo(image_handle);
 		if (EFI_ERROR(efi_status)) {
 			perror(L"Netboot parsing failed: %r\n", efi_status);
@@ -1121,7 +1134,7 @@ EFI_STATUS start_image(EFI_HANDLE image_handle, CHAR16 *ImagePath)
 		}
 		data = sourcebuffer;
 		datasize = sourcesize;
-	} else if (find_httpboot(li->DeviceHandle)) {
+	} else if (find_httpboot(shim_li->DeviceHandle)) {
 		efi_status = httpboot_fetch_buffer (image_handle,
 						    &sourcebuffer,
 						    &sourcesize);
@@ -1136,7 +1149,7 @@ EFI_STATUS start_image(EFI_HANDLE image_handle, CHAR16 *ImagePath)
 		/*
 		 * Read the new executable off disk
 		 */
-		efi_status = load_image(li, &data, &datasize, PathName);
+		efi_status = load_image(shim_li, &data, &datasize, PathName);
 		if (EFI_ERROR(efi_status)) {
 			perror(L"Failed to load image %s: %r\n",
 			       PathName, efi_status);
@@ -1155,13 +1168,13 @@ EFI_STATUS start_image(EFI_HANDLE image_handle, CHAR16 *ImagePath)
 	 * We need to modify the loaded image protocol entry before running
 	 * the new binary, so back it up
 	 */
-	CopyMem(&li_bak, li, sizeof(li_bak));
+	CopyMem(&shim_li_bak, shim_li, sizeof(shim_li_bak));
 
 	/*
 	 * Update the loaded image with the second stage loader file path
 	 */
-	li->FilePath = FileDevicePath(NULL, PathName);
-	if (!li->FilePath) {
+	shim_li->FilePath = FileDevicePath(NULL, PathName);
+	if (!shim_li->FilePath) {
 		perror(L"Unable to update loaded image file path\n");
 		efi_status = EFI_OUT_OF_RESOURCES;
 		goto restore;
@@ -1170,7 +1183,7 @@ EFI_STATUS start_image(EFI_HANDLE image_handle, CHAR16 *ImagePath)
 	/*
 	 * Verify and, if appropriate, relocate and execute the executable
 	 */
-	efi_status = handle_image(data, datasize, li, &entry_point,
+	efi_status = handle_image(data, datasize, shim_li, &entry_point,
 				  &alloc_address, &alloc_pages);
 	if (EFI_ERROR(efi_status)) {
 		perror(L"Failed to load image: %r\n", efi_status);
@@ -1187,13 +1200,7 @@ EFI_STATUS start_image(EFI_HANDLE image_handle, CHAR16 *ImagePath)
 	efi_status = entry_point(image_handle, systab);
 
 restore:
-	if (li->FilePath)
-		FreePool(li->FilePath);
-
-	/*
-	 * Restore our original loaded image values
-	 */
-	CopyMem(li, &li_bak, sizeof(li_bak));
+	restore_loaded_image();
 done:
 	if (PathName)
 		FreePool(PathName);