[efi] Add support for installing EFI configuration tables

Add the ability to install and uninstall arbitrary EFI configuration
tables.

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

src/include/ipxe/efi/efi_table.h

@@ -0,0 +1,37 @@
+#ifndef _IPXE_EFI_TABLE_H
+#define _IPXE_EFI_TABLE_H
+
+/** @file
+ *
+ * EFI configuration tables
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <ipxe/efi/efi.h>
+
+/** An installable EFI configuration table type */
+struct efi_table {
+	/** Table GUID */
+	EFI_GUID *guid;
+	/**
+	 * Determine length of table
+	 *
+	 * @v data		Configuration table data (presumed valid)
+	 * @ret len		Length of table
+	 *
+	 * EFI does not record the length of installed configuration
+	 * tables.  Consumers must understand the specific type of
+	 * table in order to be able to determine its length from the
+	 * contents.
+	 */
+	size_t ( * len ) ( const void *data );
+};
+
+extern void * efi_find_table ( EFI_GUID *guid );
+extern int efi_install_table ( struct efi_table *table, const void *data,
+			       void **backup );
+extern int efi_uninstall_table ( struct efi_table *table, void **backup );
+
+#endif /* _IPXE_EFI_TABLE_H */

src/include/ipxe/errfile.h

@@ -85,6 +85,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define ERRFILE_efi_service	       ( ERRFILE_CORE | 0x002d0000 )
 #define ERRFILE_null_smbios	       ( ERRFILE_CORE | 0x002e0000 )
 #define ERRFILE_efi_open	       ( ERRFILE_CORE | 0x002f0000 )
+#define ERRFILE_efi_table	       ( ERRFILE_CORE | 0x00300000 )
 
 #define ERRFILE_eisa		     ( ERRFILE_DRIVER | 0x00000000 )
 #define ERRFILE_isa		     ( ERRFILE_DRIVER | 0x00010000 )

src/interface/efi/efi_init.c

@@ -25,6 +25,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <ipxe/init.h>
 #include <ipxe/rotate.h>
 #include <ipxe/efi/efi.h>
+#include <ipxe/efi/efi_table.h>
 #include <ipxe/efi/efi_driver.h>
 #include <ipxe/efi/efi_path.h>
 #include <ipxe/efi/efi_cmdline.h>
@@ -103,24 +104,6 @@ static EFIAPI void efi_shutdown_hook ( EFI_EVENT event __unused,
 	shutdown_boot();
 }
 
-/**
- * Look up EFI configuration table
- *
- * @v guid		Configuration table GUID
- * @ret table		Configuration table, or NULL
- */
-static void * efi_find_table ( EFI_GUID *guid ) {
-	unsigned int i;
-
-	for ( i = 0 ; i < efi_systab->NumberOfTableEntries ; i++ ) {
-		if ( memcmp ( &efi_systab->ConfigurationTable[i].VendorGuid,
-			      guid, sizeof ( *guid ) ) == 0 )
-			return efi_systab->ConfigurationTable[i].VendorTable;
-	}
-
-	return NULL;
-}
-
 /**
  * Construct a stack cookie value
  *

src/interface/efi/efi_table.c

@@ -0,0 +1,178 @@
+/*
+ * Copyright (C) 2025 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <assert.h>
+#include <errno.h>
+#include <string.h>
+#include <ipxe/efi/efi.h>
+#include <ipxe/efi/efi_table.h>
+
+/** @file
+ *
+ * EFI configuration tables
+ *
+ */
+
+/**
+ * Look up EFI configuration table
+ *
+ * @v guid		Configuration table GUID
+ * @ret table		Configuration table, or NULL
+ */
+void * efi_find_table ( EFI_GUID *guid ) {
+	void *table;
+	unsigned int i;
+
+	/* Scan for installed table */
+	for ( i = 0 ; i < efi_systab->NumberOfTableEntries ; i++ ) {
+		if ( memcmp ( &efi_systab->ConfigurationTable[i].VendorGuid,
+			      guid, sizeof ( *guid ) ) == 0 ) {
+			table = efi_systab->ConfigurationTable[i].VendorTable;
+			DBGC ( guid, "EFITAB %s is at %p\n",
+			       efi_guid_ntoa ( guid ), table );
+			return table;
+		}
+	}
+
+	return NULL;
+}
+
+/**
+ * Install EFI configuration table
+ *
+ * @v table		Configuration table type
+ * @v data		Configuration table data, or NULL to uninstall
+ * @v backup		Table backup, or NULL to not back up old table
+ * @ret rc		Return status code
+ */
+int efi_install_table ( struct efi_table *table, const void *data,
+			void **backup ) {
+	EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
+	EFI_GUID *guid = table->guid;
+	void *copy;
+	void *new;
+	void *old;
+	size_t old_len;
+	size_t new_len;
+	EFI_STATUS efirc;
+	int rc;
+
+	/* Get currently installed table, if any */
+	old = efi_find_table ( guid );
+	old_len = ( old ? table->len ( old ) : 0 );
+
+	/* Create backup copy, if applicable */
+	if ( old_len && backup ) {
+		if ( ( efirc = bs->AllocatePool ( EfiBootServicesData, old_len,
+						  &copy ) ) != 0 ) {
+			rc = -EEFI ( efirc );
+			goto err_backup;
+		}
+		memcpy ( copy, old, old_len );
+		DBGC ( table, "EFITAB %s %p+%#zx backed up\n",
+		       efi_guid_ntoa ( guid ), old, old_len );
+	} else {
+		copy = NULL;
+	}
+
+	/* Create installable runtime services data copy, if applicable */
+	new_len = ( data ? table->len ( data ) : 0 );
+	if ( new_len ) {
+		if ( ( efirc = bs->AllocatePool ( EfiRuntimeServicesData,
+						  new_len, &new ) ) != 0 ) {
+			rc = -EEFI ( efirc );
+			goto err_allocate;
+		}
+		memcpy ( new, data, new_len );
+	} else {
+		new = NULL;
+	}
+
+	/* (Un)install configuration table, if applicable */
+	if ( new || old ) {
+		if ( ( efirc = bs->InstallConfigurationTable ( guid,
+							       new ) ) != 0 ) {
+			rc = -EEFI ( efirc );
+			DBGC ( table, "EFITAB %s could not install: %s\n",
+			       efi_guid_ntoa ( guid ), strerror ( rc ) );
+			goto err_install;
+		}
+		if ( old ) {
+			DBGC ( table, "EFITAB %s %p+%#zx uninstalled\n",
+			       efi_guid_ntoa ( guid ), old, old_len );
+		}
+		if ( new ) {
+			DBGC ( table, "EFITAB %s %p+%#zx installed\n",
+			       efi_guid_ntoa ( guid ), new, new_len );
+		}
+	}
+
+	/* Record backup copy, if applicable */
+	if ( backup ) {
+		if ( *backup )
+			bs->FreePool ( *backup );
+		*backup = copy;
+	}
+
+	/* Sanity check */
+	assert ( efi_find_table ( guid ) == new );
+
+	return 0;
+
+ err_install:
+	if ( new )
+		bs->FreePool ( new );
+ err_allocate:
+	if ( copy )
+		bs->FreePool ( copy );
+ err_backup:
+	return rc;
+}
+
+/**
+ * Uninstall EFI configuration table
+ *
+ * @v table		Configuration table type
+ * @v backup		Table backup (or NULL to not restore old table)
+ * @ret rc		Return status code
+ */
+int efi_uninstall_table ( struct efi_table *table, void **backup ) {
+	EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
+	void *old;
+	int rc;
+
+	/* Uninstall or reinstall as applicable */
+	old = ( backup ? *backup : NULL );
+	if ( ( rc = efi_install_table ( table, old, NULL ) ) != 0 )
+		return rc;
+
+	/* Free backup copy, if applicable */
+	if ( backup && *backup ) {
+		bs->FreePool ( *backup );
+		*backup = NULL;
+	}
+
+	return 0;
+}