lib/smbios-parser.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * Copyright (C) 2020, Bachmann electronic GmbH
 */

#define LOG_CATEGORY	LOGC_BOOT

#include <common.h>
#include <smbios.h>

static inline int verify_checksum(const struct smbios_entry *e)
{
	/*
	 * Checksums for SMBIOS tables are calculated to have a value, so that
	 * the sum over all bytes yields zero (using unsigned 8 bit arithmetic).
	 */
	u8 *byte = (u8 *)e;
	u8 sum = 0;

	for (int i = 0; i < e->length; i++)
		sum += byte[i];

	return sum;
}

const struct smbios_entry *smbios_entry(u64 address, u32 size)
{
	const struct smbios_entry *entry = (struct smbios_entry *)(uintptr_t)address;

	if (!address | !size)
		return NULL;

	if (memcmp(entry->anchor, "_SM_", 4))
		return NULL;

	if (verify_checksum(entry))
		return NULL;

	return entry;
}

static const struct smbios_header *next_header(const struct smbios_header *curr)
{
	u8 *pos = ((u8 *)curr) + curr->length;

	/* search for _double_ NULL bytes */
	while (!((*pos == 0) && (*(pos + 1) == 0)))
		pos++;

	/* step behind the double NULL bytes */
	pos += 2;

	return (struct smbios_header *)pos;
}

const struct smbios_header *smbios_header(const struct smbios_entry *entry, int type)
{
	const unsigned int num_header = entry->struct_count;
	const struct smbios_header *header = (struct smbios_header *)entry->struct_table_address;

	for (unsigned int i = 0; i < num_header; i++) {
		if (header->type == type)
			return header;

		header = next_header(header);
	}

	return NULL;
}

static const char *string_from_smbios_table(const struct smbios_header *header,
                                           int idx)
{
	unsigned int i = 1;
	u8 *pos;

	if (!header)
		return NULL;

	pos = ((u8 *)header) + header->length;

	while (i < idx) {
		if (*pos == 0x0)
			i++;

		pos++;
	}

	return (const char *)pos;
}

const char *smbios_string(const struct smbios_header *header, int index)
{
	if (!header)
		return NULL;

	return string_from_smbios_table(header, index);
}

int smbios_update_version_full(void *smbios_tab, const char *version)
{
	const struct smbios_header *hdr;
	struct smbios_type0 *bios;
	uint old_len, len;
	char *ptr;

	log_info("Updating SMBIOS table at %p\n", smbios_tab);
	hdr = smbios_header(smbios_tab, SMBIOS_BIOS_INFORMATION);
	if (!hdr)
		return log_msg_ret("tab", -ENOENT);
	bios = (struct smbios_type0 *)hdr;
	ptr = (char *)smbios_string(hdr, bios->bios_ver);
	if (!ptr)
		return log_msg_ret("str", -ENOMEDIUM);

	/*
	 * This string is supposed to have at least enough bytes and is
	 * padded with spaces. Update it, taking care not to move the
	 * \0 terminator, so that other strings in the string table
	 * are not disturbed. See smbios_add_string()
	 */
	old_len = strnlen(ptr, SMBIOS_STR_MAX);
	len = strnlen(version, SMBIOS_STR_MAX);
	if (len > old_len)
		return log_ret(-ENOSPC);

	log_debug("Replacing SMBIOS type 0 version string '%s'\n", ptr);
	memcpy(ptr, version, len);
#ifdef LOG_DEBUG
	print_buffer((ulong)ptr, ptr, 1, old_len + 1, 0);
#endif

	return 0;
}