vbnv_cmos.c

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/* SPDX-License-Identifier: GPL-2.0-only */
 
#include <bootstate.h>
#include <boot/coreboot_tables.h>
#include <console/console.h>
#include <types.h>
#include <pc80/mc146818rtc.h>
#include <security/vboot/vbnv.h>
#include <security/vboot/vbnv_layout.h>
 
static void clear_vbnv_battery_cutoff_flag(uint8_t *vbnv_copy)
{
        /*
         * Currently battery cutoff is done in payload stage, which does not
         * update backup VBNV. And doing battery cutoff will invalidate CMOS.
         * This means for every reboot after cutoff, read_vbnv_cmos will reload
         * backup VBNV and try to cutoff again, causing endless reboot loop.
         * So we should always clear battery cutoff flag from loaded backup.
         */
        if (vbnv_copy[MISC_FLAGS_OFFSET] & MISC_FLAGS_BATTERY_CUTOFF_MASK) {
                printk(BIOS_INFO, "VBNV: Remove battery cut-off request.\n");
                vbnv_copy[MISC_FLAGS_OFFSET] &= ~MISC_FLAGS_BATTERY_CUTOFF_MASK;
                regen_vbnv_crc(vbnv_copy);
        }
}
 
/* Return non-zero if backup was used. */
static int restore_from_backup(uint8_t *vbnv_copy)
{
        if (!CONFIG(VBOOT_VBNV_CMOS_BACKUP_TO_FLASH))
                return 0;
 
        printk(BIOS_INFO, "VBNV: CMOS invalid, restoring from flash\n");
        read_vbnv_flash(vbnv_copy);
 
        if (verify_vbnv(vbnv_copy)) {
                clear_vbnv_battery_cutoff_flag(vbnv_copy);
                save_vbnv_cmos(vbnv_copy);
                printk(BIOS_INFO, "VBNV: Flash backup restored\n");
                return 1;
        }
 
        printk(BIOS_INFO, "VBNV: Restore from flash failed\n");
 
        return 0;
}
 
void read_vbnv_cmos(uint8_t *vbnv_copy)
{
        int i;
 
        for (i = 0; i < VBOOT_VBNV_BLOCK_SIZE; i++)
                vbnv_copy[i] = cmos_read(CONFIG_VBOOT_VBNV_OFFSET + 14 + i);
 
        /* Verify contents before attempting a restore from backup storage. */
        if (verify_vbnv(vbnv_copy))
                return;
 
        restore_from_backup(vbnv_copy);
}
 
void save_vbnv_cmos(const uint8_t *vbnv_copy)
{
        int i;
 
        for (i = 0; i < VBOOT_VBNV_BLOCK_SIZE; i++)
                cmos_write(vbnv_copy[i], CONFIG_VBOOT_VBNV_OFFSET + 14 + i);
}
 
void vbnv_init_cmos(uint8_t *vbnv_copy)
{
        /* If no CMOS failure just defer to the normal read path for checking
           vbnv contents' integrity. */
        if (!vbnv_cmos_failed())
                return;
 
        /* In the case of CMOS failure force the backup. If backup wasn't used
           force the vbnv CMOS to be reset. */
        if (!restore_from_backup(vbnv_copy)) {
                vbnv_reset(vbnv_copy);
                /* This parallels the vboot_reference implementation. */
                vbnv_copy[HEADER_OFFSET] = HEADER_SIGNATURE |
                        HEADER_FIRMWARE_SETTINGS_RESET |
                        HEADER_KERNEL_SETTINGS_RESET;
                regen_vbnv_crc(vbnv_copy);
                save_vbnv_cmos(vbnv_copy);
        }
}
 
void lb_table_add_vbnv_cmos(struct lb_header *header)
{
        struct lb_range *vbnv;
 
        vbnv = (struct lb_range *)lb_new_record(header);
        vbnv->tag = LB_TAG_VBNV;
        vbnv->size = sizeof(*vbnv);
        vbnv->range_start = CONFIG_VBOOT_VBNV_OFFSET + 14;
        vbnv->range_size = VBOOT_VBNV_BLOCK_SIZE;
}
 
#if CONFIG(VBOOT_VBNV_CMOS_BACKUP_TO_FLASH)
static void back_up_vbnv_cmos(void *unused)
{
        uint8_t vbnv_cmos[VBOOT_VBNV_BLOCK_SIZE];
 
        /* Read current VBNV from CMOS. */
        read_vbnv_cmos(vbnv_cmos);
 
        /* Save to flash, will only be saved if different. */
        save_vbnv_flash(vbnv_cmos);
}
BOOT_STATE_INIT_ENTRY(BS_POST_DEVICE, BS_ON_EXIT, back_up_vbnv_cmos, NULL);
#endif