[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 <[email protected]>

src/interface/efi/efi_autoexec.c

@@ -24,11 +24,14 @@
 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/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>
 
@@ -169,6 +172,175 @@ static int efi_autoexec_filesystem ( EFI_HANDLE device ) {
 	return rc;
 }
 
+/**
+ * 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;
+	EFI_PXE_BASE_CODE_MODE *mode;
+	EFI_PXE_BASE_CODE_PACKET *packet;
+	union {
+		struct in_addr in;
+		EFI_IP_ADDRESS ip;
+	} server;
+	size_t filename_max;
+	char *filename;
+	char *sep;
+	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;
+	}
+
+	/* Do not attempt to parse DHCPv6 packets */
+	mode = u.pxe->Mode;
+	if ( mode->UsingIpv6 ) {
+		rc = -ENOTSUP;
+		DBGC ( device, "EFI %s has IPv6 PXE base code\n",
+		       efi_handle_name ( device ) );
+		goto err_ipv6;
+	}
+
+	/* Identify relevant reply packet */
+	if ( mode->PxeReplyReceived &&
+	     mode->PxeReply.Dhcpv4.BootpBootFile[0] ) {
+		/* Use boot filename if present in PXE reply */
+		DBGC ( device, "EFI %s using PXE reply filename\n",
+		       efi_handle_name ( device ) );
+		packet = &mode->PxeReply;
+	} else if ( mode->DhcpAckReceived &&
+		    mode->DhcpAck.Dhcpv4.BootpBootFile[0] ) {
+		/* Otherwise, use boot filename if present in DHCPACK */
+		DBGC ( device, "EFI %s using DHCPACK filename\n",
+		       efi_handle_name ( device ) );
+		packet = &mode->DhcpAck;
+	} else if ( mode->ProxyOfferReceived &&
+		    mode->ProxyOffer.Dhcpv4.BootpBootFile[0] ) {
+		/* Otherwise, use boot filename if present in ProxyDHCPOFFER */
+		DBGC ( device, "EFI %s using ProxyDHCPOFFER filename\n",
+		       efi_handle_name ( device ) );
+		packet = &mode->ProxyOffer;
+	} else {
+		/* No boot filename available */
+		rc = -ENOENT;
+		DBGC ( device, "EFI %s has no PXE boot filename\n",
+		       efi_handle_name ( device ) );
+		goto err_packet;
+	}
+
+	/* Allocate filename */
+	filename_max = ( sizeof ( packet->Dhcpv4.BootpBootFile )
+			 + ( sizeof ( efi_autoexec_name ) - 1 /* NUL */ )
+			 + 1 /* NUL */ );
+	filename = zalloc ( filename_max );
+	if ( ! filename ) {
+		rc = -ENOMEM;
+		goto err_filename;
+	}
+
+	/* Extract next-server address and boot filename */
+	memset ( &server, 0, sizeof ( server ) );
+	memcpy ( &server.in, packet->Dhcpv4.BootpSiAddr,
+		 sizeof ( server.in ) );
+	memcpy ( filename, packet->Dhcpv4.BootpBootFile,
+		 sizeof ( packet->Dhcpv4.BootpBootFile ) );
+
+	/* 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_packet:
+ err_ipv6:
+	bs->CloseProtocol ( device, &efi_pxe_base_code_protocol_guid,
+			    efi_image_handle, device );
+ err_pxe:
+	return rc;
+}
+
 /**
  * Load autoexec script
  *
@@ -186,6 +358,10 @@ int efi_autoexec_load ( EFI_HANDLE device ) {
 	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;
 }