[efi] Install our own disk I/O protocol and claim exclusive use of it

The EFI FAT filesystem driver has a bug: if a block device contains no
FAT filesystem but does have an EFI_SIMPLE_FILE_SYSTEM_PROTOCOL
instance, the FAT driver will assume that it must have previously
installed the EFI_SIMPLE_FILE_SYSTEM_PROTOCOL.  This causes the FAT
driver to claim control of our device, and to refuse to stop driving
it, which prevents us from later uninstalling correctly.

Work around this bug by opening the disk I/O protocol ourselves,
thereby preventing the FAT driver from opening it.

Note that the alternative approach of opening the block I/O protocol
(and thereby in theory preventing DiskIo from attaching to the block
I/O protocol) causes an endless loop of calls to our DRIVER_STOP
method when starting the EFI shell.  I have no idea why this is.

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

1 files changed, 104 insertions, 13 deletions

diff --git a/src/interface/efi/efi_file.c b/src/interface/efi/efi_file.c
index 4c482d2e..f8713750 100644
--- a/src/interface/efi/efi_file.c
+++ b/src/interface/efi/efi_file.c
@@ -36,6 +36,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <ipxe/efi/efi.h>
 #include <ipxe/efi/Protocol/SimpleFileSystem.h>
 #include <ipxe/efi/Protocol/BlockIo.h>
+#include <ipxe/efi/Protocol/DiskIo.h>
 #include <ipxe/efi/Guid/FileInfo.h>
 #include <ipxe/efi/Guid/FileSystemInfo.h>
 #include <ipxe/efi/efi_strings.h>
@@ -55,6 +56,10 @@ static EFI_GUID efi_file_system_info_id = EFI_FILE_SYSTEM_INFO_ID;
 static EFI_GUID efi_block_io_protocol_guid
 	= EFI_BLOCK_IO_PROTOCOL_GUID;
 
+/** EFI disk I/O protocol GUID */
+static EFI_GUID efi_disk_io_protocol_guid
+	= EFI_DISK_IO_PROTOCOL_GUID;
+
 /** EFI media ID */
 #define EFI_MEDIA_ID_MAGIC 0x69505845
 
@@ -506,7 +511,7 @@ static EFI_STATUS EFIAPI
 efi_block_io_read_blocks ( EFI_BLOCK_IO_PROTOCOL *this __unused,
 			   UINT32 MediaId __unused, EFI_LBA lba __unused,
 			   UINTN len __unused, VOID *data __unused ) {
-	return EFI_DEVICE_ERROR;
+	return EFI_NO_MEDIA;
 }
 
 /** Dummy block I/O write */
@@ -514,7 +519,7 @@ static EFI_STATUS EFIAPI
 efi_block_io_write_blocks ( EFI_BLOCK_IO_PROTOCOL *this __unused,
 			    UINT32 MediaId __unused, EFI_LBA lba __unused,
 			    UINTN len __unused, VOID *data __unused ) {
-	return EFI_DEVICE_ERROR;
+	return EFI_NO_MEDIA;
 }
 
 /** Dummy block I/O flush */
@@ -541,6 +546,29 @@ static EFI_BLOCK_IO_PROTOCOL efi_block_io_protocol = {
 	.FlushBlocks = efi_block_io_flush_blocks,
 };
 
+/** Dummy disk I/O read */
+static EFI_STATUS EFIAPI
+efi_disk_io_read_disk ( EFI_DISK_IO_PROTOCOL *this __unused,
+			UINT32 MediaId __unused, UINT64 offset __unused,
+			UINTN len __unused, VOID *data __unused ) {
+	return EFI_NO_MEDIA;
+}
+
+/** Dummy disk I/O write */
+static EFI_STATUS EFIAPI
+efi_disk_io_write_disk ( EFI_DISK_IO_PROTOCOL *this __unused,
+			 UINT32 MediaId __unused, UINT64 offset __unused,
+			 UINTN len __unused, VOID *data __unused ) {
+	return EFI_NO_MEDIA;
+}
+
+/** Dummy EFI disk I/O protocol */
+static EFI_DISK_IO_PROTOCOL efi_disk_io_protocol = {
+	.Revision = EFI_DISK_IO_PROTOCOL_REVISION,
+	.ReadDisk = efi_disk_io_read_disk,
+	.WriteDisk = efi_disk_io_write_disk,
+};
+
 /**
  * Install EFI simple file system protocol
  *
@@ -549,29 +577,79 @@ static EFI_BLOCK_IO_PROTOCOL efi_block_io_protocol = {
  */
 int efi_file_install ( EFI_HANDLE *handle ) {
 	EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
+	union {
+		EFI_DISK_IO_PROTOCOL *diskio;
+		void *interface;
+	} diskio;
 	EFI_STATUS efirc;
 	int rc;
 
-	/* Install the simple file system protocol and the block I/O
-	 * protocol.  We don't have a block device, but large parts of
-	 * the EDK2 codebase make the assumption that file systems are
-	 * normally attached to block devices, and so we create a
-	 * dummy block device on the same handle just to keep things
-	 * looking normal.
+	/* Install the simple file system protocol, block I/O
+	 * protocol, and disk I/O protocol.  We don't have a block
+	 * device, but large parts of the EDK2 codebase make the
+	 * assumption that file systems are normally attached to block
+	 * devices, and so we create a dummy block device on the same
+	 * handle just to keep things looking normal.
 	 */
 	if ( ( efirc = bs->InstallMultipleProtocolInterfaces (
 			handle,
 			&efi_block_io_protocol_guid,
 			&efi_block_io_protocol,
+			&efi_disk_io_protocol_guid,
+			&efi_disk_io_protocol,
 			&efi_simple_file_system_protocol_guid,
 			&efi_simple_file_system_protocol, NULL ) ) != 0 ) {
 		rc = -EEFI ( efirc );
-		DBGC ( handle, "Could not install simple file system protocol: "
-		       "%s\n", strerror ( rc ) );
-		return rc;
+		DBGC ( handle, "Could not install simple file system "
+		       "protocols: %s\n", strerror ( rc ) );
+		goto err_install;
+	}
+
+	/* The FAT filesystem driver has a bug: if a block device
+	 * contains no FAT filesystem but does have an
+	 * EFI_SIMPLE_FILE_SYSTEM_PROTOCOL instance, the FAT driver
+	 * will assume that it must have previously installed the
+	 * EFI_SIMPLE_FILE_SYSTEM_PROTOCOL.  This causes the FAT
+	 * driver to claim control of our device, and to refuse to
+	 * stop driving it, which prevents us from later uninstalling
+	 * correctly.
+	 *
+	 * Work around this bug by opening the disk I/O protocol
+	 * ourselves, thereby preventing the FAT driver from opening
+	 * it.
+	 *
+	 * Note that the alternative approach of opening the block I/O
+	 * protocol (and thereby in theory preventing DiskIo from
+	 * attaching to the block I/O protocol) causes an endless loop
+	 * of calls to our DRIVER_STOP method when starting the EFI
+	 * shell.  I have no idea why this is.
+	 */
+	if ( ( efirc = bs->OpenProtocol ( *handle, &efi_disk_io_protocol_guid,
+					  &diskio.interface, efi_image_handle,
+					  *handle,
+					  EFI_OPEN_PROTOCOL_BY_DRIVER ) ) != 0){
+		rc = -EEFI ( efirc );
+		DBGC ( handle, "Could not open disk I/O protocol: %s\n",
+		       strerror ( rc ) );
+		goto err_open;
 	}
+	assert ( diskio.diskio == &efi_disk_io_protocol );
 
 	return 0;
+
+	bs->CloseProtocol ( *handle, &efi_disk_io_protocol_guid,
+			    efi_image_handle, *handle );
+ err_open:
+	bs->UninstallMultipleProtocolInterfaces (
+			*handle,
+			&efi_simple_file_system_protocol_guid,
+			&efi_simple_file_system_protocol,
+			&efi_disk_io_protocol_guid,
+			&efi_disk_io_protocol,
+			&efi_block_io_protocol_guid,
+			&efi_block_io_protocol, NULL );
+ err_install:
+	return rc;
 }
 
 /**
@@ -581,16 +659,29 @@ int efi_file_install ( EFI_HANDLE *handle ) {
  */
 void efi_file_uninstall ( EFI_HANDLE handle ) {
 	EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
+	EFI_STATUS efirc;
+	int rc;
+
+	/* Close our own disk I/O protocol */
+	bs->CloseProtocol ( handle, &efi_disk_io_protocol_guid,
+			    efi_image_handle, handle );
 
 	/* We must install the file system protocol first, since
 	 * otherwise the EDK2 code will attempt to helpfully uninstall
 	 * it when the block I/O protocol is uninstalled, leading to a
 	 * system lock-up.
 	 */
-	bs->UninstallMultipleProtocolInterfaces (
+	if ( ( efirc = bs->UninstallMultipleProtocolInterfaces (
 			handle,
 			&efi_simple_file_system_protocol_guid,
 			&efi_simple_file_system_protocol,
+			&efi_disk_io_protocol_guid,
+			&efi_disk_io_protocol,
 			&efi_block_io_protocol_guid,
-			&efi_block_io_protocol, NULL );
+			&efi_block_io_protocol, NULL ) ) != 0 ) {
+		rc = -EEFI ( efirc );
+		DBGC ( handle, "Could not uninstall simple file system "
+		       "protocols: %s\n", strerror ( rc ) );
+		/* Oh dear */
+	}
 }