[efi] Add support for executing images via a shim

Add support for using a shim as a helper to execute an EFI image.
When a shim has been specified via shim(), the shim image will be
passed to LoadImage() instead of the selected EFI image and the
command line will be prepended with the name of the selected EFI
image.  The selected EFI image will be accessible to the shim via the
virtual filesystem as a hidden file.

Reduce the Secure Boot attack surface by removing, where possible, the
spurious requirement for a third party second stage loader binary such
as GRUB to be used solely in order to call the "shim lock protocol"
entry point.

Do not install the EFI PXE APIs when using a shim, since if shim finds
EFI_PXE_BASE_CODE_PROTOCOL on the loaded image's device handle then it
will attempt to download files afresh instead of using the files
already downloaded by iPXE and exposed via the EFI_SIMPLE_FILE_SYSTEM
protocol.  (Experience shows that there is no point in trying to get a
fix for this upstreamed into shim.)

Signed-off-by: Michael Brown <mcb30@ipxe.org>

5 files changed, 76 insertions, 0 deletions

diff --git a/src/include/ipxe/efi/efi_image.h b/src/include/ipxe/efi/efi_image.h
new file mode 100644
index 0000000..0fc0402
--- /dev/null
+++ b/src/include/ipxe/efi/efi_image.h
@@ -0,0 +1,27 @@
+#ifndef _IPXE_EFI_IMAGE_H
+#define _IPXE_EFI_IMAGE_H
+
+/** @file
+ *
+ * EFI images
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <ipxe/image.h>
+
+extern struct image_type efi_image_type[] __image_type ( PROBE_NORMAL );
+
+/**
+ * Check if EFI image can be loaded directly
+ *
+ * @v image		EFI image
+ * @ret can_load	EFI image can be loaded directly
+ */
+static inline int efi_can_load ( struct image *image ) {
+
+	return ( image->type == efi_image_type );
+}
+
+#endif /* _IPXE_EFI_IMAGE_H */
diff --git a/src/include/ipxe/efi/efi_shim.h b/src/include/ipxe/efi/efi_shim.h
new file mode 100644
index 0000000..ad8d24d
--- /dev/null
+++ b/src/include/ipxe/efi/efi_shim.h
@@ -0,0 +1,23 @@
+#ifndef _IPXE_EFI_SHIM_H
+#define _IPXE_EFI_SHIM_H
+
+/** @file
+ *
+ * UEFI shim special handling
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <ipxe/image.h>
+#include <ipxe/efi/efi.h>
+
+extern int efi_shim_require_loader;
+extern int efi_shim_allow_pxe;
+extern struct image_tag efi_shim __image_tag;
+
+extern int efi_shim_install ( struct image *shim, EFI_HANDLE handle,
+			      wchar_t **cmdline );
+extern void efi_shim_uninstall ( void );
+
+#endif /* _IPXE_EFI_SHIM_H */
diff --git a/src/include/ipxe/errfile.h b/src/include/ipxe/errfile.h
index 235611a..daa038c 100644
--- a/src/include/ipxe/errfile.h
+++ b/src/include/ipxe/errfile.h
@@ -405,6 +405,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define ERRFILE_dhe		      ( ERRFILE_OTHER | 0x005a0000 )
 #define ERRFILE_efi_cmdline	      ( ERRFILE_OTHER | 0x005b0000 )
 #define ERRFILE_efi_rng		      ( ERRFILE_OTHER | 0x005c0000 )
+#define ERRFILE_efi_shim	      ( ERRFILE_OTHER | 0x005d0000 )
 
 /** @} */
 
diff --git a/src/include/ipxe/image.h b/src/include/ipxe/image.h
index cd51188..bfbf236 100644
--- a/src/include/ipxe/image.h
+++ b/src/include/ipxe/image.h
@@ -257,6 +257,15 @@ static inline void image_untrust ( struct image *image ) {
 }
 
 /**
+ * Mark image as hidden
+ *
+ * @v image		Image
+ */
+static inline void image_hide ( struct image *image ) {
+	image->flags |= IMAGE_HIDDEN;
+}
+
+/**
  * Tag image
  *
  * @v image		Image
diff --git a/src/include/usr/shimmgmt.h b/src/include/usr/shimmgmt.h
new file mode 100644
index 0000000..5030607
--- /dev/null
+++ b/src/include/usr/shimmgmt.h
@@ -0,0 +1,16 @@
+#ifndef _USR_SHIMMGMT_H
+#define _USR_SHIMMGMT_H
+
+/** @file
+ *
+ * EFI shim management
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <ipxe/image.h>
+
+extern int shim ( struct image *image, int require_loader, int allow_pxe );
+
+#endif /* _USR_SHIMMGMT_H */