bootconfig: Load boot config from the tail of initrd

Load the extended boot config data from the tail of initrd
image. If there is an SKC data there, it has
[(u32)size][(u32)checksum] header (in really, this is a
footer) at the end of initrd. If the checksum (simple sum
of bytes) is match, this starts parsing it from there.

Link: http://lkml.kernel.org/r/157867222435.17873.9936667353335606867.stgit@devnote2Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

init/Kconfig

@@ -1217,6 +1217,7 @@ endif
 
 config BOOT_CONFIG
 	bool "Boot config support"
+	depends on BLK_DEV_INITRD
 	select LIBXBC
 	default y
 	help

init/main.c

@@ -28,6 +28,7 @@
 #include <linux/initrd.h>
 #include <linux/memblock.h>
 #include <linux/acpi.h>
+#include <linux/bootconfig.h>
 #include <linux/console.h>
 #include <linux/nmi.h>
 #include <linux/percpu.h>
@@ -245,6 +246,58 @@ static int __init loglevel(char *str)
 
 early_param("loglevel", loglevel);
 
+#ifdef CONFIG_BOOT_CONFIG
+u32 boot_config_checksum(unsigned char *p, u32 size)
+{
+	u32 ret = 0;
+
+	while (size--)
+		ret += *p++;
+
+	return ret;
+}
+
+static void __init setup_boot_config(void)
+{
+	u32 size, csum;
+	char *data, *copy;
+	u32 *hdr;
+
+	if (!initrd_end)
+		return;
+
+	hdr = (u32 *)(initrd_end - 8);
+	size = hdr[0];
+	csum = hdr[1];
+
+	if (size >= XBC_DATA_MAX)
+		return;
+
+	data = ((void *)hdr) - size;
+	if ((unsigned long)data < initrd_start)
+		return;
+
+	if (boot_config_checksum((unsigned char *)data, size) != csum)
+		return;
+
+	copy = memblock_alloc(size + 1, SMP_CACHE_BYTES);
+	if (!copy) {
+		pr_err("Failed to allocate memory for boot config\n");
+		return;
+	}
+
+	memcpy(copy, data, size);
+	copy[size] = '\0';
+
+	if (xbc_init(copy) < 0)
+		pr_err("Failed to parse boot config\n");
+	else
+		pr_info("Load boot config: %d bytes\n", size);
+}
+#else
+#define setup_boot_config()	do { } while (0)
+#endif
+
 /* Change NUL term back to "=", to make "param" the whole string. */
 static int __init repair_env_string(char *param, char *val,
 				    const char *unused, void *arg)
@@ -595,6 +648,7 @@ asmlinkage __visible void __init start_kernel(void)
 	pr_notice("%s", linux_banner);
 	early_security_init();
 	setup_arch(&command_line);
+	setup_boot_config();
 	setup_command_line(command_line);
 	setup_nr_cpu_ids();
 	setup_per_cpu_areas();