x86/EFI: add code interfacing with the secure boot shim

... to validate the kernel image (which is required to be in PE
format, as is e.g. the case for the Linux bzImage when built with
CONFIG_EFI_STUB).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/efi/boot.c
+++ b/xen/arch/x86/efi/boot.c
@@ -24,6 +24,18 @@
 #include <asm/msr.h>
 #include <asm/processor.h>
 
+#define SHIM_LOCK_PROTOCOL_GUID \
+  { 0x605dab50, 0xe046, 0x4300, {0xab, 0xb6, 0x3d, 0xd8, 0x10, 0xdd, 0x8b, 0x23} }
+
+typedef EFI_STATUS
+(/* _not_ EFIAPI */ *EFI_SHIM_LOCK_VERIFY) (
+    IN VOID *Buffer,
+    IN UINT32 Size);
+
+typedef struct {
+    EFI_SHIM_LOCK_VERIFY Verify;
+} EFI_SHIM_LOCK_PROTOCOL;
+
 extern char start[];
 extern u32 cpuid_ext_features;
 
@@ -640,12 +652,14 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SY
     static EFI_GUID __initdata gop_guid = EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID;
     static EFI_GUID __initdata bio_guid = BLOCK_IO_PROTOCOL;
     static EFI_GUID __initdata devp_guid = DEVICE_PATH_PROTOCOL;
+    static EFI_GUID __initdata shim_lock_guid = SHIM_LOCK_PROTOCOL_GUID;
     EFI_LOADED_IMAGE *loaded_image;
     EFI_STATUS status;
     unsigned int i, argc;
     CHAR16 **argv, *file_name, *cfg_file_name = NULL;
     UINTN cols, rows, depth, size, map_key, info_size, gop_mode = ~0;
     EFI_HANDLE *handles = NULL;
+    EFI_SHIM_LOCK_PROTOCOL *shim_lock;
     EFI_GRAPHICS_OUTPUT_PROTOCOL *gop = NULL;
     EFI_GRAPHICS_OUTPUT_MODE_INFORMATION *mode_info;
     EFI_FILE_HANDLE dir_handle;
@@ -835,6 +849,11 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SY
     read_file(dir_handle, s2w(&name), &kernel);
     efi_bs->FreePool(name.w);
 
+    if ( !EFI_ERROR(efi_bs->LocateProtocol(&shim_lock_guid, NULL,
+                    (void **)&shim_lock)) &&
+         shim_lock->Verify(kernel.ptr, kernel.size) != EFI_SUCCESS )
+        blexit(L"Dom0 kernel image could not be verified\r\n");
+
     name.s = get_value(&cfg, section.s, "ramdisk");
     if ( name.s )
     {