src/drivers/smmstore/store.c

/*
 * This file is part of the coreboot project.
 *
 * Copyright (C) 2018 The Chromium OS Authors.  All rights reserved.
 *
 * 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; version 2 of the License.
 *
 * 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.
 */

#include <boot_device.h>
#include <cbfs.h>
#include <commonlib/region.h>
#include <console/console.h>
#include <smmstore.h>
#include <string.h>

/*
 * The region format is still not finalized, but so far it looks like this:
 *   (
 *    uint32le_t key_sz
 *    uint32le_t value_sz
 *    uint8_t key[key_sz]
 *    uint8_t value[value_sz]
 *    uint8_t active
 *    align to 4 bytes
 *  )*
 *   uint32le_t endmarker = 0xffffffff
 *
 * active needs to be set to 0x00 for the entry to be valid. This satisfies
 * the constraint that entries are either complete or will be ignored, as long
 * as flash is written sequentially and into a fully erased block.
 *
 * Future additions to the format will split the region in half with an active
 * block marker to allow safe compaction (ie. write the new data in the unused
 * region, mark it active after the write completed). Otherwise a well-timed
 * crash/reboot could clear out all variables.
 */

/*
 * Return a region device that points into the store file.
 *
 * It's the image builder's responsibility to make it block aligned so that
 * erase works without destroying other data.
 *
 * It doesn't cache the location to cope with flash changing underneath (eg
 * due to an update)
 *
 * returns 0 on success, -1 on failure
 * outputs the valid store rdev in rstore
 */
static int lookup_store(struct region_device *rstore)
{
	struct cbfsf file;
	if (cbfs_locate_file_in_region(&file,
		CONFIG_SMMSTORE_REGION, CONFIG_SMMSTORE_FILENAME, NULL) < 0) {
		printk(BIOS_WARNING, "smm store: "
			"Unable to find SMM store file in region '%s'\n",
			CONFIG_SMMSTORE_REGION);
		return -1;
	}

	cbfs_file_data(rstore, &file);

	return 0;
}

/*
 * Read entire store into user provided buffer
 *
 * returns 0 on success, -1 on failure
 * writes up to `*bufsize` bytes into `buf` and updates `*bufsize`
 */
int smmstore_read_region(void *buf, ssize_t *bufsize)
{
	struct region_device store;

	if (bufsize == NULL)
		return -1;

	*bufsize = 0;
	if (lookup_store(&store) < 0) {
		printk(BIOS_WARNING, "reading region failed\n");
		return -1;
	}

	ssize_t tx = min(*bufsize, region_device_sz(&store));
	*bufsize = rdev_readat(&store, buf, 0, tx);

	if (*bufsize < 0)
		return -1;

	return 0;
}

/*
 * Append data to region
 *
 * Returns 0 on success, -1 on failure
 */
int smmstore_append_data(void *key, uint32_t key_sz,
	void *value, uint32_t value_sz)
{
	struct region_device store;

	if (lookup_store(&store) < 0) {
		printk(BIOS_WARNING, "reading region failed\n");
		return -1;
	}

	ssize_t data_sz = region_device_sz(&store);

	/* scan for end */
	ssize_t end = 0;
	uint32_t k_sz, v_sz;
	while (end < data_sz) {
		/* make odd corner cases identifiable, eg. invalid v_sz */
		k_sz = 0;

		if (rdev_readat(&store, &k_sz, end, sizeof(k_sz)) < 0) {
			printk(BIOS_WARNING, "failed reading key size\n");
			return -1;
		}

		/* found the end */
		if (k_sz == 0xffffffff)
			break;

		/* something is fishy here:
		 * Avoid wrapping (since data_size < MAX_UINT32_T / 2) while
		 * other problems are covered by the loop condition
		 */
		if (k_sz > data_sz) {
			printk(BIOS_WARNING, "key size out of bounds\n");
			return -1;
		}

		if (rdev_readat(&store, &v_sz, end + 4, sizeof(v_sz)) < 0) {
			printk(BIOS_WARNING, "failed reading value size\n");
			return -1;
		}

		if (v_sz > data_sz) {
			printk(BIOS_WARNING, "value size out of bounds\n");
			return -1;
		}

		end += 8 + k_sz + v_sz + 1;
		end = ALIGN_UP(end, sizeof(uint32_t));
	}

	printk(BIOS_WARNING, "used smm store size might be 0x%zx bytes\n", end);

	if (k_sz != 0xffffffff) {
		printk(BIOS_WARNING,
			"eof of data marker looks invalid: 0x%x\n", k_sz);
		return -1;
	}

	printk(BIOS_WARNING, "used size looks legit\n");

	printk(BIOS_WARNING, "open (%zx, %zx) for writing\n",
		region_device_offset(&store), region_device_sz(&store));
	if (boot_device_rw_subregion(&store.region, &store) < 0) {
		printk(BIOS_WARNING, "couldn't open store for writing\n");
		return -1;
	}

	uint32_t record_sz = 8 + key_sz + value_sz + 1;
	if (end + record_sz >= data_sz) {
		printk(BIOS_WARNING, "not enough space for new data\n");
		return -1;
	}

	if (rdev_writeat(&store, &key_sz, end, 4) != 4) {
		printk(BIOS_WARNING, "failed writing key size\n");
	}
	end += 4;
	if (rdev_writeat(&store, &value_sz, end, 4) != 4) {
		printk(BIOS_WARNING, "failed writing value size\n");
	}
	end += 4;
	if (rdev_writeat(&store, key, end, key_sz) != key_sz) {
		printk(BIOS_WARNING, "failed writing key data\n");
	}
	end += key_sz;
	if (rdev_writeat(&store, value, end, value_sz) != value_sz) {
		printk(BIOS_WARNING, "failed writing value data\n");
	}
	end += value_sz;
	uint8_t nul = 0;
	if (rdev_writeat(&store, &nul, end, 1) != 1) {
		printk(BIOS_WARNING, "failed writing termination\n");
	}

	return 0;
}

/*
 * Clear region
 *
 * Returns 0 on success, -1 on failure, including partial erase
 */
int smmstore_clear_region(void)
{
	struct region_device store;

	if (lookup_store(&store) < 0) {
		printk(BIOS_WARNING, "smm store: reading region failed\n");
		return -1;
	}

	ssize_t res = rdev_eraseat(&store, 0, region_device_sz(&store));
	if (res != region_device_sz(&store)) {
		printk(BIOS_WARNING, "smm store: erasing region failed\n");
		return -1;
	}

	return 0;
}