ima_template.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2013 Politecnico di Torino, Italy
 *                    TORSEC group -- https://security.polito.it
 *
 * Author: Roberto Sassu <roberto.sassu@polito.it>
 *
 * File: ima_template.c
 *      Helpers to manage template descriptors.
 */

#include <linux/rculist.h>
#include "ima.h"
#include "ima_template_lib.h"

enum header_fields { HDR_PCR, HDR_DIGEST, HDR_TEMPLATE_NAME,
		     HDR_TEMPLATE_DATA, HDR__LAST };

static struct ima_template_desc builtin_templates[] = {
	{.name = IMA_TEMPLATE_IMA_NAME, .fmt = IMA_TEMPLATE_IMA_FMT},
	{.name = "ima-ng", .fmt = "d-ng|n-ng"},
	{.name = "ima-sig", .fmt = "d-ng|n-ng|sig"},
	{.name = "ima-buf", .fmt = "d-ng|n-ng|buf"},
	{.name = "ima-modsig", .fmt = "d-ng|n-ng|sig|d-modsig|modsig"},
	{.name = "", .fmt = ""},	/* placeholder for a custom format */
};

static LIST_HEAD(defined_templates);
static DEFINE_SPINLOCK(template_list);

static const struct ima_template_field supported_fields[] = {
	{.field_id = "d", .field_init = ima_eventdigest_init,
	 .field_show = ima_show_template_digest},
	{.field_id = "n", .field_init = ima_eventname_init,
	 .field_show = ima_show_template_string},
	{.field_id = "d-ng", .field_init = ima_eventdigest_ng_init,
	 .field_show = ima_show_template_digest_ng},
	{.field_id = "n-ng", .field_init = ima_eventname_ng_init,
	 .field_show = ima_show_template_string},
	{.field_id = "sig", .field_init = ima_eventsig_init,
	 .field_show = ima_show_template_sig},
	{.field_id = "buf", .field_init = ima_eventbuf_init,
	 .field_show = ima_show_template_buf},
	{.field_id = "d-modsig", .field_init = ima_eventdigest_modsig_init,
	 .field_show = ima_show_template_digest_ng},
	{.field_id = "modsig", .field_init = ima_eventmodsig_init,
	 .field_show = ima_show_template_sig},
};

/*
 * Used when restoring measurements carried over from a kexec. 'd' and 'n' don't
 * need to be accounted for since they shouldn't be defined in the same template
 * description as 'd-ng' and 'n-ng' respectively.
 */
#define MAX_TEMPLATE_NAME_LEN sizeof("d-ng|n-ng|sig|buf|d-modisg|modsig")

static struct ima_template_desc *ima_template;

/**
 * ima_template_has_modsig - Check whether template has modsig-related fields.
 * @ima_template: IMA template to check.
 *
 * Tells whether the given template has fields referencing a file's appended
 * signature.
 */
bool ima_template_has_modsig(const struct ima_template_desc *ima_template)
{
	int i;

	for (i = 0; i < ima_template->num_fields; i++)
		if (!strcmp(ima_template->fields[i]->field_id, "modsig") ||
		    !strcmp(ima_template->fields[i]->field_id, "d-modsig"))
			return true;

	return false;
}

static int __init ima_template_setup(char *str)
{
	struct ima_template_desc *template_desc;
	int template_len = strlen(str);

	if (ima_template)
		return 1;

	ima_init_template_list();

	/*
	 * Verify that a template with the supplied name exists.
	 * If not, use CONFIG_IMA_DEFAULT_TEMPLATE.
	 */
	template_desc = lookup_template_desc(str);
	if (!template_desc) {
		pr_err("template %s not found, using %s\n",
		       str, CONFIG_IMA_DEFAULT_TEMPLATE);
		return 1;
	}

	/*
	 * Verify whether the current hash algorithm is supported
	 * by the 'ima' template.
	 */
	if (template_len == 3 && strcmp(str, IMA_TEMPLATE_IMA_NAME) == 0 &&
	    ima_hash_algo != HASH_ALGO_SHA1 && ima_hash_algo != HASH_ALGO_MD5) {
		pr_err("template does not support hash alg\n");
		return 1;
	}

	ima_template = template_desc;
	return 1;
}
__setup("ima_template=", ima_template_setup);

static int __init ima_template_fmt_setup(char *str)
{
	int num_templates = ARRAY_SIZE(builtin_templates);

	if (ima_template)
		return 1;

	if (template_desc_init_fields(str, NULL, NULL) < 0) {
		pr_err("format string '%s' not valid, using template %s\n",
		       str, CONFIG_IMA_DEFAULT_TEMPLATE);
		return 1;
	}

	builtin_templates[num_templates - 1].fmt = str;
	ima_template = builtin_templates + num_templates - 1;

	return 1;
}
__setup("ima_template_fmt=", ima_template_fmt_setup);

struct ima_template_desc *lookup_template_desc(const char *name)
{
	struct ima_template_desc *template_desc;
	int found = 0;

	rcu_read_lock();
	list_for_each_entry_rcu(template_desc, &defined_templates, list) {
		if ((strcmp(template_desc->name, name) == 0) ||
		    (strcmp(template_desc->fmt, name) == 0)) {
			found = 1;
			break;
		}
	}
	rcu_read_unlock();
	return found ? template_desc : NULL;
}

static const struct ima_template_field *
lookup_template_field(const char *field_id)
{
	int i;

	for (i = 0; i < ARRAY_SIZE(supported_fields); i++)
		if (strncmp(supported_fields[i].field_id, field_id,
			    IMA_TEMPLATE_FIELD_ID_MAX_LEN) == 0)
			return &supported_fields[i];
	return NULL;
}

static int template_fmt_size(const char *template_fmt)
{
	char c;
	int template_fmt_len = strlen(template_fmt);
	int i = 0, j = 0;

	while (i < template_fmt_len) {
		c = template_fmt[i];
		if (c == '|')
			j++;
		i++;
	}

	return j + 1;
}

int template_desc_init_fields(const char *template_fmt,
			      const struct ima_template_field ***fields,
			      int *num_fields)
{
	const char *template_fmt_ptr;
	const struct ima_template_field *found_fields[IMA_TEMPLATE_NUM_FIELDS_MAX];
	int template_num_fields;
	int i, len;

	if (num_fields && *num_fields > 0) /* already initialized? */
		return 0;

	template_num_fields = template_fmt_size(template_fmt);

	if (template_num_fields > IMA_TEMPLATE_NUM_FIELDS_MAX) {
		pr_err("format string '%s' contains too many fields\n",
		       template_fmt);
		return -EINVAL;
	}

	for (i = 0, template_fmt_ptr = template_fmt; i < template_num_fields;
	     i++, template_fmt_ptr += len + 1) {
		char tmp_field_id[IMA_TEMPLATE_FIELD_ID_MAX_LEN + 1];

		len = strchrnul(template_fmt_ptr, '|') - template_fmt_ptr;
		if (len == 0 || len > IMA_TEMPLATE_FIELD_ID_MAX_LEN) {
			pr_err("Invalid field with length %d\n", len);
			return -EINVAL;
		}

		memcpy(tmp_field_id, template_fmt_ptr, len);
		tmp_field_id[len] = '\0';
		found_fields[i] = lookup_template_field(tmp_field_id);
		if (!found_fields[i]) {
			pr_err("field '%s' not found\n", tmp_field_id);
			return -ENOENT;
		}
	}

	if (fields && num_fields) {
		*fields = kmalloc_array(i, sizeof(*fields), GFP_KERNEL);
		if (*fields == NULL)
			return -ENOMEM;

		memcpy(*fields, found_fields, i * sizeof(*fields));
		*num_fields = i;
	}

	return 0;
}

void ima_init_template_list(void)
{
	int i;

	if (!list_empty(&defined_templates))
		return;

	spin_lock(&template_list);
	for (i = 0; i < ARRAY_SIZE(builtin_templates); i++) {
		list_add_tail_rcu(&builtin_templates[i].list,
				  &defined_templates);
	}
	spin_unlock(&template_list);
}

struct ima_template_desc *ima_template_desc_current(void)
{
	if (!ima_template) {
		ima_init_template_list();
		ima_template =
		    lookup_template_desc(CONFIG_IMA_DEFAULT_TEMPLATE);
	}
	return ima_template;
}

int __init ima_init_template(void)
{
	struct ima_template_desc *template = ima_template_desc_current();
	int result;

	result = template_desc_init_fields(template->fmt,
					   &(template->fields),
					   &(template->num_fields));
	if (result < 0)
		pr_err("template %s init failed, result: %d\n",
		       (strlen(template->name) ?
		       template->name : template->fmt), result);

	return result;
}

static struct ima_template_desc *restore_template_fmt(char *template_name)
{
	struct ima_template_desc *template_desc = NULL;
	int ret;

	ret = template_desc_init_fields(template_name, NULL, NULL);
	if (ret < 0) {
		pr_err("attempting to initialize the template \"%s\" failed\n",
			template_name);
		goto out;
	}

	template_desc = kzalloc(sizeof(*template_desc), GFP_KERNEL);
	if (!template_desc)
		goto out;

	template_desc->name = "";
	template_desc->fmt = kstrdup(template_name, GFP_KERNEL);
	if (!template_desc->fmt)
		goto out;

	spin_lock(&template_list);
	list_add_tail_rcu(&template_desc->list, &defined_templates);
	spin_unlock(&template_list);
out:
	return template_desc;
}

static int ima_restore_template_data(struct ima_template_desc *template_desc,
				     void *template_data,
				     int template_data_size,
				     struct ima_template_entry **entry)
{
	struct tpm_digest *digests;
	int ret = 0;
	int i;

	*entry = kzalloc(struct_size(*entry, template_data,
				     template_desc->num_fields), GFP_NOFS);
	if (!*entry)
		return -ENOMEM;

	digests = kcalloc(NR_BANKS(ima_tpm_chip) + ima_extra_slots,
			  sizeof(*digests), GFP_NOFS);
	if (!digests) {
		kfree(*entry);
		return -ENOMEM;
	}

	(*entry)->digests = digests;

	ret = ima_parse_buf(template_data, template_data + template_data_size,
			    NULL, template_desc->num_fields,
			    (*entry)->template_data, NULL, NULL,
			    ENFORCE_FIELDS | ENFORCE_BUFEND, "template data");
	if (ret < 0) {
		kfree((*entry)->digests);
		kfree(*entry);
		return ret;
	}

	(*entry)->template_desc = template_desc;
	for (i = 0; i < template_desc->num_fields; i++) {
		struct ima_field_data *field_data = &(*entry)->template_data[i];
		u8 *data = field_data->data;

		(*entry)->template_data[i].data =
			kzalloc(field_data->len + 1, GFP_KERNEL);
		if (!(*entry)->template_data[i].data) {
			ret = -ENOMEM;
			break;
		}
		memcpy((*entry)->template_data[i].data, data, field_data->len);
		(*entry)->template_data_len += sizeof(field_data->len);
		(*entry)->template_data_len += field_data->len;
	}

	if (ret < 0) {
		ima_free_template_entry(*entry);
		*entry = NULL;
	}

	return ret;
}

/* Restore the serialized binary measurement list without extending PCRs. */
int ima_restore_measurement_list(loff_t size, void *buf)
{
	char template_name[MAX_TEMPLATE_NAME_LEN];
	unsigned char zero[TPM_DIGEST_SIZE] = { 0 };

	struct ima_kexec_hdr *khdr = buf;
	struct ima_field_data hdr[HDR__LAST] = {
		[HDR_PCR] = {.len = sizeof(u32)},
		[HDR_DIGEST] = {.len = TPM_DIGEST_SIZE},
	};

	void *bufp = buf + sizeof(*khdr);
	void *bufendp;
	struct ima_template_entry *entry;
	struct ima_template_desc *template_desc;
	DECLARE_BITMAP(hdr_mask, HDR__LAST);
	unsigned long count = 0;
	int ret = 0;

	if (!buf || size < sizeof(*khdr))
		return 0;

	if (ima_canonical_fmt) {
		khdr->version = le16_to_cpu(khdr->version);
		khdr->count = le64_to_cpu(khdr->count);
		khdr->buffer_size = le64_to_cpu(khdr->buffer_size);
	}

	if (khdr->version != 1) {
		pr_err("attempting to restore a incompatible measurement list");
		return -EINVAL;
	}

	if (khdr->count > ULONG_MAX - 1) {
		pr_err("attempting to restore too many measurements");
		return -EINVAL;
	}

	bitmap_zero(hdr_mask, HDR__LAST);
	bitmap_set(hdr_mask, HDR_PCR, 1);
	bitmap_set(hdr_mask, HDR_DIGEST, 1);

	/*
	 * ima kexec buffer prefix: version, buffer size, count
	 * v1 format: pcr, digest, template-name-len, template-name,
	 *	      template-data-size, template-data
	 */
	bufendp = buf + khdr->buffer_size;
	while ((bufp < bufendp) && (count++ < khdr->count)) {
		int enforce_mask = ENFORCE_FIELDS;

		enforce_mask |= (count == khdr->count) ? ENFORCE_BUFEND : 0;
		ret = ima_parse_buf(bufp, bufendp, &bufp, HDR__LAST, hdr, NULL,
				    hdr_mask, enforce_mask, "entry header");
		if (ret < 0)
			break;

		if (hdr[HDR_TEMPLATE_NAME].len >= MAX_TEMPLATE_NAME_LEN) {
			pr_err("attempting to restore a template name that is too long\n");
			ret = -EINVAL;
			break;
		}

		/* template name is not null terminated */
		memcpy(template_name, hdr[HDR_TEMPLATE_NAME].data,
		       hdr[HDR_TEMPLATE_NAME].len);
		template_name[hdr[HDR_TEMPLATE_NAME].len] = 0;

		if (strcmp(template_name, "ima") == 0) {
			pr_err("attempting to restore an unsupported template \"%s\" failed\n",
			       template_name);
			ret = -EINVAL;
			break;
		}

		template_desc = lookup_template_desc(template_name);
		if (!template_desc) {
			template_desc = restore_template_fmt(template_name);
			if (!template_desc)
				break;
		}

		/*
		 * Only the running system's template format is initialized
		 * on boot.  As needed, initialize the other template formats.
		 */
		ret = template_desc_init_fields(template_desc->fmt,
						&(template_desc->fields),
						&(template_desc->num_fields));
		if (ret < 0) {
			pr_err("attempting to restore the template fmt \"%s\" failed\n",
			       template_desc->fmt);
			ret = -EINVAL;
			break;
		}

		ret = ima_restore_template_data(template_desc,
						hdr[HDR_TEMPLATE_DATA].data,
						hdr[HDR_TEMPLATE_DATA].len,
						&entry);
		if (ret < 0)
			break;

		if (memcmp(hdr[HDR_DIGEST].data, zero, sizeof(zero))) {
			ret = ima_calc_field_array_hash(
						&entry->template_data[0],
						entry);
			if (ret < 0) {
				pr_err("cannot calculate template digest\n");
				ret = -EINVAL;
				break;
			}
		}

		entry->pcr = !ima_canonical_fmt ? *(hdr[HDR_PCR].data) :
			     le32_to_cpu(*(hdr[HDR_PCR].data));
		ret = ima_restore_measurement_entry(entry);
		if (ret < 0)
			break;

	}
	return ret;
}