path: root/lib/bootconfig.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Extra Boot Config
 * Masami Hiramatsu <mhiramat@kernel.org>
 */

/*
 * NOTE: This is only for tools/bootconfig, because tools/bootconfig will
 * run the parser sanity test.
 * This does NOT mean lib/bootconfig.c is available in the user space.
 * However, if you change this file, please make sure the tools/bootconfig
 * has no issue on building and running.
 */
#include <linux/bootconfig.h>

#ifdef __KERNEL__
#include <linux/bug.h>
#include <linux/ctype.h>
#include <linux/errno.h>
#include <linux/cache.h>
#include <linux/compiler.h>
#include <linux/init.h>
#include <linux/moduleparam.h>
#include <linux/printk.h>
#include <linux/sprintf.h>
#include <linux/memblock.h>
#include <linux/string.h>
#include <asm/setup.h>		/* COMMAND_LINE_SIZE */

#ifdef CONFIG_BOOT_CONFIG_EMBED
/* embedded_bootconfig_data is defined in bootconfig-data.S */
extern __visible const char embedded_bootconfig_data[];
extern __visible const char embedded_bootconfig_data_end[];

const char * __init xbc_get_embedded_bootconfig(size_t *size)
{
	*size = embedded_bootconfig_data_end - embedded_bootconfig_data;
	return (*size) ? embedded_bootconfig_data : NULL;
}
#endif

#ifdef CONFIG_CMDLINE_FROM_BOOTCONFIG
/* embedded_kernel_cmdline is defined in embedded-cmdline.S */
extern __visible const char embedded_kernel_cmdline[];
extern __visible const char embedded_kernel_cmdline_end[];

/* Set once the embedded cmdline has actually been prepended. */
static bool xbc_cmdline_applied __initdata;

/*
 * str_prepend() - Prepend @src in front of the string in @dst, in place
 * @dst: NUL-terminated destination buffer, currently @dst_len bytes long
 * @dst_len: length of the current @dst string (excluding its NUL)
 * @src: bytes to prepend (not NUL-terminated)
 * @src_len: number of bytes from @src to prepend
 *
 * The caller must guarantee @dst has room for src_len + dst_len + 1 bytes.
 * Moving dst_len + 1 bytes carries @dst's NUL terminator too, so an empty
 * @dst needs no special case.
 */
static void __init str_prepend(char *dst, size_t dst_len,
			       const char *src, size_t src_len)
{
	memmove(dst + src_len, dst, dst_len + 1);
	memcpy(dst, src, src_len);
}

/**
 * xbc_prepend_embedded_cmdline() - Prepend embedded bootconfig cmdline
 * @dst: cmdline buffer to prepend into (must already contain a NUL byte)
 * @size: total capacity of @dst in bytes
 *
 * Prepend the build-time-rendered "kernel" subtree of the embedded
 * bootconfig to @dst. The rendered string already ends with a single
 * space (the xbc_snprint_cmdline() invariant), which serves as the
 * separator between the embedded keys and any existing content of @dst.
 * On overflow, log an error and leave @dst untouched rather than
 * silently truncating: booting without the embedded values is better
 * than refusing to boot, and the error message tells the user why
 * their embedded keys are missing.
 *
 * Intended to be called from setup_arch() before parse_early_param() so
 * that early_param() handlers see the embedded values.
 */
void __init xbc_prepend_embedded_cmdline(char *dst, size_t size)
{
	size_t embed_len = embedded_kernel_cmdline_end - embedded_kernel_cmdline;
	size_t dst_len;

	if (!size || embed_len <= 1)	/* trailing NUL only */
		return;
	embed_len--;			/* exclude trailing NUL byte */

	dst_len = strnlen(dst, size);
	if (embed_len + dst_len + 1 > size) {
		pr_err("embedded bootconfig cmdline (%zu bytes) does not fit in COMMAND_LINE_SIZE with %zu bytes already used; ignoring embedded values\n",
		       embed_len, dst_len);
		return;
	}

	str_prepend(dst, dst_len, embedded_kernel_cmdline, embed_len);
	xbc_cmdline_applied = true;
}

/**
 * xbc_embedded_cmdline_applied() - Did the embedded cmdline get prepended?
 *
 * Return true if xbc_prepend_embedded_cmdline() actually prepended the
 * embedded "kernel" subtree. setup_boot_config() uses this to avoid
 * rendering the same keys a second time.
 */
bool __init xbc_embedded_cmdline_applied(void)
{
	return xbc_cmdline_applied;
}
#endif	/* CONFIG_CMDLINE_FROM_BOOTCONFIG */

/* parse_args() callback: flag when the "bootconfig" parameter is present. */
static int __init bootconfig_optin(char *param, char *val,
				   const char *unused, void *arg)
{
	if (!strcmp(param,