init/main: read bootconfig header with get_unaligned_le32()

get_boot_config_from_initrd() scans up to 3 bytes before initrd_end to
handle GRUB 4-byte alignment.  As a result, the bootconfig header
immediately preceding the magic may be unaligned.

Read the size and checksum fields with get_unaligned_le32() instead of
casting to u32 * and using le32_to_cpu(), avoiding potential unaligned
access and silencing sparse "cast to restricted __le32" warnings.

Sparse warnings (gcc + C=1):
  init/main.c:292:16: warning: cast to restricted __le32
  init/main.c:293:16: warning: cast to restricted __le32

No functional change intended.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Sun Jian <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: ahjf-07

init/main.c

@@ -104,6 +104,7 @@
 #include <linux/pidfs.h>
 #include <linux/ptdump.h>
 #include <linux/time_namespace.h>
+#include <linux/unaligned.h>
 #include <net/net_namespace.h>
 
 #include <asm/io.h>
@@ -270,7 +271,7 @@ static void * __init get_boot_config_from_initrd(size_t *_size)
 {
 	u32 size, csum;
 	char *data;
-	u32 *hdr;
+	u8 *hdr;
 	int i;
 
 	if (!initrd_end)
@@ -289,9 +290,9 @@ static void * __init get_boot_config_from_initrd(size_t *_size)
 	return NULL;
 
 found:
-	hdr = (u32 *)(data - 8);
-	size = le32_to_cpu(hdr[0]);
-	csum = le32_to_cpu(hdr[1]);
+	hdr = (u8 *)(data - 8);
+	size = get_unaligned_le32(hdr);
+	csum = get_unaligned_le32(hdr + 4);
 
 	data = ((void *)hdr) - size;
 	if ((unsigned long)data < initrd_start) {