disk: put a magic at the end of the boot sector

Put a magic signature at the end of the boot sector, and a backpointer
to the code that contains the pointer to the main code extent.  This
is useful for integrity-checking tools, and could help the installer
in the future.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

4 files changed, 19 insertions, 9 deletions

diff --git a/core/diskboot.inc b/core/diskboot.inc
index 4a730b0b..574db456 100644
--- a/core/diskboot.inc
+++ b/core/diskboot.inc
@@ -262,6 +262,7 @@ eddcheck:
 ; with parsing the superblock and root directory; it doesn't fit
 ; together with EBIOS support, unfortunately.
 ;
+Sect1Load:
 		mov eax,strict dword Sect1Ptr0_VAL	; 0xdeadbeef
 Sect1Ptr0	equ $-4
 		mov edx,strict dword Sect1Ptr1_VAL	; 0xfeedface
@@ -273,9 +274,8 @@ Sect1Ptr1	equ $-4
 		cmp dword [ldlinux_magic+4],LDLINUX_MAGIC^HEXDATE
 		jne kaboom
 
-		; Go for it...
-		jmp 0:ldlinux_ent
-
+		; Go for it!  This also normalizes CS:IP.
+		jmp ldlinux_ent
 
 ;
 ; getonesec: load a single disk linear sector EDX:EAX into the buffer
@@ -423,8 +423,10 @@ xint13:
 bailmsg:	db 'Boot error', 0Dh, 0Ah, 0
 
 		; This fails if the boot sector overflowsg
-		zb 1FEh-($-$$)
+		zb 1F8h-($-$$)
 
+bs_magic	dd LDLINUX_MAGIC
+bs_link		dw (Sect1Load - bootsec) | BS_MAGIC_VER
 bootsignature	dw 0xAA55
 
 ;
diff --git a/core/diskfs.inc b/core/diskfs.inc
index a04a4f0d..fc80a153 100644
--- a/core/diskfs.inc
+++ b/core/diskfs.inc
@@ -2,7 +2,7 @@
 ; -----------------------------------------------------------------------
 ;   
 ;   Copyright 1994-2009 H. Peter Anvin - All Rights Reserved
-;   Copyright 2009 Intel Corporation; author: H. Peter Anvin
+;   Copyright 2009-2011 Intel Corporation; author: H. Peter Anvin
 ;
 ;   This program is free software; you can redistribute it and/or modify
 ;   it under the terms of the GNU General Public License as published by
@@ -27,6 +27,9 @@ retry_count	equ 16			; How patient are we with the disk?
 %assign HIGHMEM_SLOP 0			; Avoid this much memory near the top
 LDLINUX_MAGIC	equ 0x3eb202fe		; A random number to identify ourselves with
 
+; This indicates the general format of the last few bytes in the boot sector
+BS_MAGIC_VER	equ 0x1b << 9
+
 SECTOR_SHIFT	equ 9
 SECTOR_SIZE	equ (1 << SECTOR_SHIFT)
 
diff --git a/core/diskstart.inc b/core/diskstart.inc
index 4e2d1fcf..b3c09286 100644
--- a/core/diskstart.inc
+++ b/core/diskstart.inc
@@ -1,7 +1,7 @@
 ; -----------------------------------------------------------------------
 ;
 ;   Copyright 1994-2009 H. Peter Anvin - All Rights Reserved
-;   Copyright 2009-2010 Intel Corporation; author: H. Peter Anvin
+;   Copyright 2009-2011 Intel Corporation; author: H. Peter Anvin
 ;
 ;   This program is free software; you can redistribute it and/or modify
 ;   it under the terms of the GNU General Public License as published by
@@ -92,7 +92,8 @@ ldlinux_ent:
 ; value in CS, but we don't want to deal with that anymore from now
 ; on.
 ;
-		sti		; In case of broken INT 13h BIOSes
+		jmp 0:.next	; Normalize CS:IP
+.next:		sti		; In case of broken INT 13h BIOSes
 
 ;
 ; Tell the user we got this far
diff --git a/libinstaller/syslxint.h b/libinstaller/syslxint.h
index 14a7fc2b..80c40f76 100644
--- a/libinstaller/syslxint.h
+++ b/libinstaller/syslxint.h
@@ -1,6 +1,7 @@
 /* ----------------------------------------------------------------------- *
  *
  *   Copyright 2007-2008 H. Peter Anvin - All Rights Reserved
+ *   Copyright 2009-2011 Intel Corporation; author: H. Peter Anvin
  *
  *   This program is free software; you can redistribute it and/or modify
  *   it under the terms of the GNU General Public License as published by
@@ -156,6 +157,7 @@ void memcpy_from_sl(void *dst, const void *src, size_t len);
 #endif
 
 #define LDLINUX_MAGIC	0x3eb202fe
+#define BS_MAGIC_VER	(0x1b << 9)
 
 /* Patch area for disk-based installers */
 struct patch_area {
@@ -214,7 +216,7 @@ struct boot_sector {
 	    uint32_t VolumeID;
 	    char VolumeLabel[11];
 	    char FileSysType[8];
-	    uint8_t Code[448];
+	    uint8_t Code[442];
 	} __attribute__ ((packed)) bs16;
 	struct {
 	    uint32_t FATSz32;
@@ -230,10 +232,12 @@ struct boot_sector {
 	    uint32_t VolumeID;
 	    char VolumeLabel[11];
 	    char FileSysType[8];
-	    uint8_t Code[420];
+	    uint8_t Code[414];
 	} __attribute__ ((packed)) bs32;
     } __attribute__ ((packed));
 
+    uint32_t bsMagic;
+    uint16_t bsForwardPtr;
     uint16_t bsSignature;
 } __attribute__ ((packed));