ima_kexec.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2016 IBM Corporation
 *
 * Authors:
 * Thiago Jung Bauermann <[email protected]>
 * Mimi Zohar <[email protected]>
 */

#include <linux/seq_file.h>
#include <linux/vmalloc.h>
#include <linux/kexec.h>
#include <linux/of.h>
#include <linux/ima.h>
#include <linux/reboot.h>
#include <asm/page.h>
#include "ima.h"

#ifdef CONFIG_IMA_KEXEC
#define IMA_KEXEC_EVENT_LEN 256

static bool ima_kexec_update_registered;
static struct seq_file ima_kexec_file;
static size_t kexec_segment_size;
static void *ima_kexec_buffer;

static void ima_free_kexec_file_buf(struct seq_file *sf)
{
	vfree(sf->buf);
	sf->buf = NULL;
	sf->size = 0;
	sf->read_pos = 0;
	sf->count = 0;
}

void ima_measure_kexec_event(const char *event_name)
{
	char ima_kexec_event[IMA_KEXEC_EVENT_LEN];
	size_t buf_size = 0;
	long len;
	int n;

	buf_size = ima_get_binary_runtime_size();
	len = atomic_long_read(&ima_htable.len);

	n = scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
		      "kexec_segment_size=%lu;ima_binary_runtime_size=%lu;"
		      "ima_runtime_measurements_count=%ld;",
		      kexec_segment_size, buf_size, len);

	ima_measure_critical_data("ima_kexec", event_name, ima_kexec_event, n, false, NULL, 0);
}

static int ima_alloc_kexec_file_buf(size_t segment_size)
{
	/*
	 * kexec 'load' may be called multiple times.
	 * Free and realloc the buffer only if the segment_size is
	 * changed from the previous kexec 'load' call.
	 */
	if (ima_kexec_file.buf && ima_kexec_file.size == segment_size)
		goto out;

	ima_free_kexec_file_buf(&ima_kexec_file);

	/* segment size can't change between kexec load and execute */
	ima_kexec_file.buf = vmalloc(segment_size);
	if (!ima_kexec_file.buf)
		return -ENOMEM;

	ima_kexec_file.size = segment_size;

out:
	ima_kexec_file.read_pos = 0;
	ima_kexec_file.count = sizeof(struct ima_kexec_hdr);	/* reserved space */
	ima_measure_kexec_event("kexec_load");

	return 0;
}

static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
				     unsigned long segment_size)
{
	struct ima_queue_entry *qe;
	struct ima_kexec_hdr khdr;
	int ret = 0;

	/* segment size can't change between kexec load and execute */
	if (!ima_kexec_file.buf) {
		pr_err("Kexec file buf not allocated\n");
		return -EINVAL;
	}

	memset(&khdr, 0, sizeof(khdr));
	khdr.version = 1;
	/* This is an append-only list, no need to hold the RCU read lock */
	list_for_each_entry_rcu(qe, &ima_measurements, later, true) {
		if (ima_kexec_file.count < ima_kexec_file.size) {
			khdr.count++;
			ima_measurements_show(&ima_kexec_file, qe);
		} else {
			ret = -EINVAL;
			break;
		}
	}

	/*
	 * fill in reserved space with some buffer details
	 * (eg. version, buffer size, number of measurements)
	 */
	khdr.buffer_size = ima_kexec_file.count;
	if (ima_canonical_fmt) {
		khdr.version = cpu_to_le16(khdr.version);
		khdr.count = cpu_to_le64(khdr.count);
		khdr.buffer_size = cpu_to_le64(khdr.buffer_size);
	}
	memcpy(ima_kexec_file.buf, &khdr, sizeof(khdr));

	print_hex_dump_debug("ima dump: ", DUMP_PREFIX_NONE, 16, 1,
			     ima_kexec_file.buf, ima_kexec_file.count < 100 ?
			     ima_kexec_file.count : 100,
			     true);

	*buffer_size = ima_kexec_file.count;
	*buffer = ima_kexec_file.buf;

	return ret;
}

/*
 * Called during kexec_file_load so that IMA can add a segment to the kexec
 * image for the measurement list for the next kernel.
 *
 * This function assumes that kexec_lock is held.
 */
void ima_add_kexec_buffer(struct kimage *image)
{
	struct kexec_buf kbuf = { .image = image, .buf_align = PAGE_SIZE,
				  .buf_min = 0, .buf_max = ULONG_MAX,
				  .top_down = true };
	unsigned long binary_runtime_size;
	unsigned long extra_memory;

	/* use more understandable variable names than defined in kbuf */
	size_t kexec_buffer_size = 0;
	void *kexec_buffer = NULL;
	int ret;

	if (image->type == KEXEC_TYPE_CRASH)
		return;

	/*
	 * Reserve extra memory for measurements added during kexec.
	 */
	if (CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB <= 0)
		extra_memory = PAGE_SIZE / 2;
	else
		extra_memory = CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB * 1024;

	binary_runtime_size = ima_get_binary_runtime_size() + extra_memory;

	if (binary_runtime_size >= ULONG_MAX - PAGE_SIZE)
		kexec_segment_size = ULONG_MAX;
	else
		kexec_segment_size = ALIGN(binary_runtime_size, PAGE_SIZE);

	if ((kexec_segment_size == ULONG_MAX) ||
	    ((kexec_segment_size >> PAGE_SHIFT) > totalram_pages() / 2)) {
		pr_err("Binary measurement list too large.\n");
		return;
	}

	ret = ima_alloc_kexec_file_buf(kexec_segment_size);
	if (ret < 0) {
		pr_err("Not enough memory for the kexec measurement buffer.\n");
		return;
	}

	kbuf.buffer = kexec_buffer;
	kbuf.bufsz = kexec_buffer_size;
	kbuf.memsz = kexec_segment_size;
	image->is_ima_segment_index_set = false;
	ret = kexec_add_buffer(&kbuf);
	if (ret) {
		pr_err("Error passing over kexec measurement buffer.\n");
		vfree(kexec_buffer);
		return;
	}

	image->ima_buffer_addr = kbuf.mem;
	image->ima_buffer_size = kexec_segment_size;
	image->ima_buffer = kexec_buffer;
	image->ima_segment_index = image->nr_segments - 1;
	image->is_ima_segment_index_set = true;

	kexec_dprintk("kexec measurement buffer for the loaded kernel at 0x%lx.\n",
		      kbuf.mem);
}

/*
 * Called during kexec execute so that IMA can update the measurement list.
 */
static int ima_update_kexec_buffer(struct notifier_block *self,
				   unsigned long action, void *data)
{
	size_t buf_size = 0;
	int ret = NOTIFY_OK;
	void *buf = NULL;

	if (!kexec_in_progress) {
		pr_info("No kexec in progress.\n");
		return ret;
	}

	if (!ima_kexec_buffer) {
		pr_err("Kexec buffer not set.\n");
		return ret;
	}

	ret = ima_dump_measurement_list(&buf_size, &buf, kexec_segment_size);

	if (ret)
		pr_err("Dump measurements failed. Error:%d\n", ret);

	if (buf_size != 0)
		memcpy(ima_kexec_buffer, buf, buf_size);

	kimage_unmap_segment(ima_kexec_buffer);
	ima_kexec_buffer = NULL;

	return ret;
}

static struct notifier_block update_buffer_nb = {
	.notifier_call = ima_update_kexec_buffer,
	.priority = INT_MIN
};

/*
 * Create a mapping for the source pages that contain the IMA buffer
 * so we can update it later.
 */
void ima_kexec_post_load(struct kimage *image)
{
	if (ima_kexec_buffer) {
		kimage_unmap_segment(ima_kexec_buffer);
		ima_kexec_buffer = NULL;
	}

	if (!image->ima_buffer_addr)
		return;

	ima_kexec_buffer = kimage_map_segment(image,
					      image->ima_buffer_addr,
					      image->ima_buffer_size);
	if (!ima_kexec_buffer) {
		pr_err("Could not map measurements buffer.\n");
		return;
	}

	if (!ima_kexec_update_registered) {
		register_reboot_notifier(&update_buffer_nb);
		ima_kexec_update_registered = true;
	}
}

#endif /* IMA_KEXEC */

/*
 * Restore the measurement list from the previous kernel.
 */
void __init ima_load_kexec_buffer(void)
{
	void *kexec_buffer = NULL;
	size_t kexec_buffer_size = 0;
	int rc;

	rc = ima_get_kexec_buffer(&kexec_buffer, &kexec_buffer_size);
	switch (rc) {
	case 0:
		rc = ima_restore_measurement_list(kexec_buffer_size,
						  kexec_buffer);
		if (rc != 0)
			pr_err("Failed to restore the measurement list: %d\n",
				rc);

		ima_free_kexec_buffer();
		break;
	case -ENOTSUPP:
		pr_debug("Restoring the measurement list not supported\n");
		break;
	case -ENOENT:
		pr_debug("No measurement list to restore\n");
		break;
	default:
		pr_debug("Error restoring the measurement list: %d\n", rc);
	}
}