efi_settings.c

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/*
 * Copyright (C) 2023 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 );
FILE_SECBOOT ( PERMITTED );

/**
 * @file
 *
 * EFI variable settings
 *
 */

#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <ipxe/settings.h>
#include <ipxe/init.h>
#include <ipxe/efi/efi.h>
#include <ipxe/efi/efi_strings.h>

/** EFI variable settings scope */
static const struct settings_scope efivars_scope;

/** EFI variable settings */
static struct settings efivars;

/**
 * Check applicability of EFI variable setting
 *
 * @v settings          Settings block
 * @v setting           Setting
 * @ret applies         Setting applies within this settings block
 */
static int efivars_applies ( struct settings *settings __unused,
                             const struct setting *setting ) {

        return ( setting->scope == &efivars_scope );
}

/**
 * Find first matching EFI variable name
 *
 * @v wname             Name
 * @v guid              GUID to fill in
 * @ret rc              Return status code
 */
static int efivars_find ( const CHAR16 *wname, EFI_GUID *guid ) {
        EFI_RUNTIME_SERVICES *rs = efi_systab->RuntimeServices;
        size_t wname_len = ( ( wcslen ( wname ) + 1 ) * sizeof ( wname[0] ) );
        CHAR16 *buf;
        CHAR16 *tmp;
        UINTN size;
        EFI_STATUS efirc;
        int rc;

        /* Allocate single wNUL for first call to GetNextVariableName() */
        size = sizeof ( buf[0] );
        buf = zalloc ( size );
        if ( ! buf )
                return -ENOMEM;

        /* Iterate over all veriables */
        while ( 1 ) {

                /* Get next variable name */
                efirc = rs->GetNextVariableName ( &size, buf, guid );
                if ( efirc == EFI_BUFFER_TOO_SMALL ) {
                        tmp = realloc ( buf, size );
                        if ( ! tmp ) {
                                rc = -ENOMEM;
                                break;
                        }
                        buf = tmp;
                        efirc = rs->GetNextVariableName ( &size, buf, guid );
                }
                if ( efirc == EFI_NOT_FOUND ) {
                        rc = -ENOENT;
                        break;
                }
                if ( efirc != 0 ) {
                        rc = -EEFI ( efirc );
                        DBGC ( &efivars, "EFIVARS %s:%ls could not fetch next "
                               "variable name: %s\n",
                               efi_guid_ntoa ( guid ), buf, strerror ( rc ) );
                        break;
                }
                DBGC2 ( &efivars, "EFIVARS %s:%ls exists\n",
                        efi_guid_ntoa ( guid ), buf );

                /* Check for matching variable name */
                if ( memcmp ( wname, buf, wname_len ) == 0 ) {
                        rc = 0;
                        break;
                }
        }

        /* Free temporary buffer */
        free ( buf );

        return rc;
}

/**
 * Fetch value of EFI variable setting
 *
 * @v settings          Settings block
 * @v setting           Setting to fetch
 * @v data              Buffer to fill with setting data
 * @v len               Length of buffer
 * @ret len             Length of setting data, or negative error
 */
static int efivars_fetch ( struct settings *settings __unused,
                           struct setting *setting, void *data, size_t len ) {
        EFI_RUNTIME_SERVICES *rs = efi_systab->RuntimeServices;
        size_t name_len = strlen ( setting->name );
        CHAR16 wname[ name_len + 1 /* wNUL */ ];
        EFI_GUID guid;
        UINT32 attrs;
        UINTN size;
        void *buf;
        EFI_STATUS efirc;
        int rc;

        /* Convert name to UCS-2 */
        efi_snprintf ( wname, sizeof ( wname ), "%s", setting->name );

        /* Find variable GUID */
        if ( ( rc = efivars_find ( wname, &guid ) ) != 0 )
                goto err_find;

        /* Get variable length */
        size = 0;
        if ( ( efirc = rs->GetVariable ( wname, &guid, &attrs, &size,
                                         NULL ) != EFI_BUFFER_TOO_SMALL ) ) {
                rc = -EEFI ( efirc );
                DBGC ( &efivars, "EFIVARS %s:%ls could not get size: %s\n",
                       efi_guid_ntoa ( &guid ), wname, strerror ( rc ) );
                goto err_len;
        }

        /* Allocate temporary buffer, since GetVariable() is not
         * guaranteed to return partial data for an underlength
         * buffer.
         */
        buf = malloc ( size );
        if ( ! buf ) {
                rc = -ENOMEM;
                goto err_alloc;
        }

        /* Get variable value */
        if ( ( efirc = rs->GetVariable ( wname, &guid, &attrs, &size,
                                         buf ) ) != 0 ) {
                rc = -EEFI ( efirc );
                DBGC ( &efivars, "EFIVARS %s:%ls could not get %zd bytes: "
                       "%s\n", efi_guid_ntoa ( &guid ), wname,
                       ( ( size_t ) size ), strerror ( rc ) );
                goto err_get;
        }
        DBGC ( &efivars, "EFIVARS %s:%ls:\n", efi_guid_ntoa ( &guid ), wname );
        DBGC_HDA ( &efivars, 0, buf, size );

        /* Return setting value */
        if ( len > size )
                len = size;
        memcpy ( data, buf, len );
        if ( ! setting->type )
                setting->type = &setting_type_hex;

        /* Free temporary buffer */
        free ( buf );

        return size;

 err_get:
        free ( buf );
 err_alloc:
 err_len:
 err_find:
        return rc;
}

/** EFI variable settings operations */
static struct settings_operations efivars_operations = {
        .applies = efivars_applies,
        .fetch = efivars_fetch,
};

/** EFI variable settings */
static struct settings efivars = {
        .refcnt = NULL,
        .siblings = LIST_HEAD_INIT ( efivars.siblings ),
        .children = LIST_HEAD_INIT ( efivars.children ),
        .op = &efivars_operations,
        .default_scope = &efivars_scope,
};

/**
 * Initialise EFI variable settings
 *
 */
static void efivars_init ( void ) {
        int rc;

        /* Register settings block */
        if ( ( rc = register_settings ( &efivars, NULL, "efi" ) ) != 0 ) {
                DBGC ( &efivars, "EFIVARS could not register: %s\n",
                       strerror ( rc ) );
                return;
        }
}

/** EFI variable settings initialiser */
struct init_fn efivars_init_fn __init_fn ( INIT_NORMAL ) = {
        .name = "efivars",
        .initialise = efivars_init,
};