efi_bootmgr.c
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/*
* EFI utils
*
* Copyright (c) 2017 Rob Clark
*
* SPDX-License-Identifier: GPL-2.0+
*/
#include <common.h>
#include <charset.h>
#include <malloc.h>
#include <efi_loader.h>
static const struct efi_boot_services *bs;
static const struct efi_runtime_services *rs;
#define LOAD_OPTION_ACTIVE 0x00000001
#define LOAD_OPTION_FORCE_RECONNECT 0x00000002
#define LOAD_OPTION_HIDDEN 0x00000008
/*
* bootmgr implements the logic of trying to find a payload to boot
* based on the BootOrder + BootXXXX variables, and then loading it.
*
* TODO detecting a special key held (f9?) and displaying a boot menu
* like you would get on a PC would be clever.
*
* TODO if we had a way to write and persist variables after the OS
* has started, we'd also want to check OsIndications to see if we
* should do normal or recovery boot.
*/
/*
* See section 3.1.3 in the v2.7 UEFI spec for more details on
* the layout of EFI_LOAD_OPTION. In short it is:
*
* typedef struct _EFI_LOAD_OPTION {
* UINT32 Attributes;
* UINT16 FilePathListLength;
* // CHAR16 Description[]; <-- variable length, NULL terminated
* // EFI_DEVICE_PATH_PROTOCOL FilePathList[]; <-- FilePathListLength bytes
* // UINT8 OptionalData[];
* } EFI_LOAD_OPTION;
*/
struct load_option {
u32 attributes;
u16 file_path_length;
u16 *label;
struct efi_device_path *file_path;
u8 *optional_data;
};
/* parse an EFI_LOAD_OPTION, as described above */
static void parse_load_option(struct load_option *lo, void *ptr)
{
lo->attributes = *(u32 *)ptr;
ptr += sizeof(u32);
lo->file_path_length = *(u16 *)ptr;
ptr += sizeof(u16);
lo->label = ptr;
ptr += (utf16_strlen(lo->label) + 1) * 2;
lo->file_path = ptr;
ptr += lo->file_path_length;
lo->optional_data = ptr;
}
/* free() the result */
static void *get_var(u16 *name, const efi_guid_t *vendor,
unsigned long *size)
{
efi_guid_t *v = (efi_guid_t *)vendor;
efi_status_t ret;
void *buf = NULL;
*size = 0;
EFI_CALL(ret = rs->get_variable((s16 *)name, v, NULL, size, buf));
if (ret == EFI_BUFFER_TOO_SMALL) {
buf = malloc(*size);
EFI_CALL(ret = rs->get_variable((s16 *)name, v, NULL, size, buf));
}
if (ret != EFI_SUCCESS) {
free(buf);
*size = 0;
return NULL;
}
return buf;
}
/*
* Attempt to load load-option number 'n', returning device_path and file_path
* if successful. This checks that the EFI_LOAD_OPTION is active (enabled)
* and that the specified file to boot exists.
*/
static void *try_load_entry(uint16_t n, struct efi_device_path **device_path,
struct efi_device_path **file_path)
{
struct load_option lo;
u16 varname[] = L"Boot0000";
u16 hexmap[] = L"0123456789ABCDEF";
void *load_option, *image = NULL;
unsigned long size;
varname[4] = hexmap[(n & 0xf000) >> 12];
varname[5] = hexmap[(n & 0x0f00) >> 8];
varname[6] = hexmap[(n & 0x00f0) >> 4];
varname[7] = hexmap[(n & 0x000f) >> 0];
load_option = get_var(varname, &efi_global_variable_guid, &size);
if (!load_option)
return NULL;
parse_load_option(&lo, load_option);
if (lo.attributes & LOAD_OPTION_ACTIVE) {
efi_status_t ret;
debug("%s: trying to load \"%ls\" from %pD\n",
__func__, lo.label, lo.file_path);
ret = efi_load_image_from_path(lo.file_path, &image);
if (ret != EFI_SUCCESS)
goto error;
printf("Booting: %ls\n", lo.label);
efi_dp_split_file_path(lo.file_path, device_path, file_path);
}
error:
free(load_option);
return image;
}
/*
* Attempt to load, in the order specified by BootOrder EFI variable, the
* available load-options, finding and returning the first one that can
* be loaded successfully.
*/
void *efi_bootmgr_load(struct efi_device_path **device_path,
struct efi_device_path **file_path)
{
uint16_t *bootorder;
unsigned long size;
void *image = NULL;
int i, num;
__efi_entry_check();
bs = systab.boottime;
rs = systab.runtime;
bootorder = get_var(L"BootOrder", &efi_global_variable_guid, &size);
if (!bootorder)
goto error;
num = size / sizeof(uint16_t);
for (i = 0; i < num; i++) {
debug("%s: trying to load Boot%04X\n", __func__, bootorder[i]);
image = try_load_entry(bootorder[i], device_path, file_path);
if (image)
break;
}
free(bootorder);
error:
__efi_exit_check();
return image;
}