[efi] Attempt to fetch autoexec script via TFTP

Attempt to fetch the autoexec.ipxe script via TFTP using the PXE base
code protocol installed on the loaded image's device handle, if
present.

This provides a generic alternative to the use of an embedded script
for chainloaded binaries, which is particularly useful in a UEFI
Secure Boot environment since it allows the script to be modified
without the need to sign a new binary.

As a side effect, this also provides a third method for breaking the
PXE chainloading loop (as an alternative to requiring an embedded
script or custom DHCP server configuration).

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

src/interface/efi/efi_autoexec.c

diff --git a/src/interface/efi/efi_autoexec.c b/src/interface/efi/efi_autoexec.c
index 881c30c..7180fb8 100644
--- a/src/interface/efi/efi_autoexec.c
+++ b/src/interface/efi/efi_autoexec.c
@@ -24,11 +24,16 @@
 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #include <string.h>
+#include <stdlib.h>
 #include <errno.h>
 #include <ipxe/image.h>
 #include <ipxe/init.h>
+#include <ipxe/in.h>
+#include <ipxe/settings.h>
+#include <ipxe/cachedhcp.h>
 #include <ipxe/efi/efi.h>
 #include <ipxe/efi/efi_autoexec.h>
+#include <ipxe/efi/Protocol/PxeBaseCode.h>
 #include <ipxe/efi/Protocol/SimpleFileSystem.h>
 #include <ipxe/efi/Guid/FileInfo.h>
 
@@ -170,6 +175,146 @@
 }
 
 /**
+ * Load autoexec script from TFTP server
+ *
+ * @v device		Device handle
+ * @ret rc		Return status code
+ */
+static int efi_autoexec_tftp ( EFI_HANDLE device ) {
+	EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
+	union {
+		void *interface;
+		EFI_PXE_BASE_CODE_PROTOCOL *pxe;
+	} u;
+	union {
+		struct in_addr in;
+		EFI_IP_ADDRESS ip;
+	} server;
+	struct settings *settings;
+	size_t filename_len;
+	char *filename;
+	char *sep;
+	int len;
+	UINT64 size;
+	VOID *data;
+	EFI_STATUS efirc;
+	int rc;
+
+	/* Open PXE base code protocol */
+	if ( ( efirc = bs->OpenProtocol ( device,
+					  &efi_pxe_base_code_protocol_guid,
+					  &u.interface, efi_image_handle,
+					  device,
+					  EFI_OPEN_PROTOCOL_GET_PROTOCOL ))!=0){
+		rc = -EEFI ( efirc );
+		DBGC ( device, "EFI %s has no PXE base code instance: %s\n",
+		       efi_handle_name ( device ), strerror ( rc ) );
+		goto err_pxe;
+	}
+
+	/* Identify settings block containing cached filename, if any */
+	len = fetch_setting ( &cachedhcp_settings, &filename_setting,
+			      &settings, NULL, NULL, 0 );
+	if ( len < 0 ) {
+		rc = len;
+		DBGC ( device, "EFI %s has no PXE boot filename: %s\n",
+		       efi_handle_name ( device ), strerror ( rc ) );
+		goto err_settings;
+	}
+
+	/* Allocate filename */
+	filename_len = ( len + ( sizeof ( efi_autoexec_name ) - 1 /* NUL */ )
+			 + 1 /* NUL */ );
+	filename = malloc ( filename_len );
+	if ( ! filename ) {
+		rc = -ENOMEM;
+		goto err_filename;
+	}
+
+	/* Fetch filename and TFTP server address */
+	fetch_string_setting ( settings, &filename_setting, filename,
+			       filename_len );
+	memset ( &server, 0, sizeof ( server ) );
+	fetch_ipv4_setting ( settings, &next_server_setting, &server.in );
+
+	/* Update filename to autoexec script name */
+	sep = strrchr ( filename, '/' );
+	if ( ! sep )
+		sep = strrchr ( filename, '\\' );
+	if ( ! sep )
+		sep = ( filename - 1 );
+	strcpy ( ( sep + 1 ), efi_autoexec_name );
+
+	/* Get file size */
+	if ( ( efirc = u.pxe->Mtftp ( u.pxe,
+				      EFI_PXE_BASE_CODE_TFTP_GET_FILE_SIZE,
+				      NULL, FALSE, &size, NULL, &server.ip,
+				      ( ( UINT8 * ) filename ), NULL,
+				      FALSE ) ) != 0 ) {
+		rc = -EEFI ( efirc );
+		DBGC ( device, "EFI %s could not get size of %s:%s: %s\n",
+		       efi_handle_name ( device ), inet_ntoa ( server.in ),
+		       filename, strerror ( rc ) );
+		goto err_size;
+	}
+
+	/* Ignore zero-length files */
+	if ( ! size ) {
+		rc = -EINVAL;
+		DBGC ( device, "EFI %s has zero-length %s:%s\n",
+		       efi_handle_name ( device ), inet_ntoa ( server.in ),
+		       filename );
+		goto err_empty;
+	}
+
+	/* Allocate temporary copy */
+	if ( ( efirc = bs->AllocatePool ( EfiBootServicesData, size,
+					  &data ) ) != 0 ) {
+		rc = -EEFI ( efirc );
+		DBGC ( device, "EFI %s could not allocate %s:%s: %s\n",
+		       efi_handle_name ( device ), inet_ntoa ( server.in ),
+		       filename, strerror ( rc ) );
+		goto err_alloc;
+	}
+
+	/* Download file */
+	if ( ( efirc = u.pxe->Mtftp ( u.pxe, EFI_PXE_BASE_CODE_TFTP_READ_FILE,
+				      data, FALSE, &size, NULL, &server.ip,
+				      ( ( UINT8 * ) filename ), NULL,
+				      FALSE ) ) != 0 ) {
+		rc = -EEFI ( efirc );
+		DBGC ( device, "EFI %s could not download %s:%s: %s\n",
+		       efi_handle_name ( device ), inet_ntoa ( server.in ),
+		       filename, strerror ( rc ) );
+		goto err_download;
+	}
+
+	/* Record autoexec script */
+	efi_autoexec = data;
+	efi_autoexec_len = size;
+	data = NULL;
+	DBGC ( device, "EFI %s found %s:%s\n", efi_handle_name ( device ),
+	       inet_ntoa ( server.in ), filename );
+
+	/* Success */
+	rc = 0;
+
+ err_download:
+	if ( data )
+		bs->FreePool ( data );
+ err_alloc:
+ err_empty:
+ err_size:
+	free ( filename );
+ err_filename:
+ err_settings:
+	bs->CloseProtocol ( device, &efi_pxe_base_code_protocol_guid,
+			    efi_image_handle, device );
+ err_pxe:
+	return rc;
+}
+
+/**
  * Load autoexec script
  *
  * @v device		Device handle
@@ -186,6 +331,10 @@
 	if ( ( rc = efi_autoexec_filesystem ( device ) ) == 0 )
 		return 0;
 
+	/* Try loading via TFTP, if supported */
+	if ( ( rc = efi_autoexec_tftp ( device ) ) == 0 )
+		return 0;
+
 	return -ENOENT;
 }