kern/66248: [panic] bootloader is confused by booting from USB flash, trashes main drives boot block

[Peter Edwards]

The following reply was made to PR kern/66248; it has been noted by GNATS.

From: Peter Edwards <peadar at freebsd.org>
To: freebsd-gnats-submit at FreeBSD.org, bremner at unb.ca
Cc: julian at elischer.org, imp at bsdimp.org
Subject: Re: kern/66248: [panic] bootloader is confused by booting from USB
 flash, trashes main drives boot block
Date: Wed, 05 Jan 2005 20:53:02 +0000

 This is a multi-part message in MIME format.
 --------------070200040205060401080901
 Content-Type: text/plain; charset=us-ascii; format=flowed
 Content-Transfer-Encoding: 7bit
 
 The following patch, applied before the one above, shrinks boot0 enough 
 to squeeze the previous patch in without undeffing the BEL stuff.
 
 FWIW: The patch to fix the bug looks good to me.
 I someone gives a go-ahead, I'll commit a combined patch: I certainly 
 don't want to make a commit to boot0 and have half the FreeBSD community 
 left without a bootable machine, unless I can pass the book :-)
 
 
 --------------070200040205060401080901
 Content-Type: text/plain;
  name="boot0.smaller.patch"
 Content-Transfer-Encoding: 7bit
 Content-Disposition: inline;
  filename="boot0.smaller.patch"
 
 Index: boot0.S
 ===================================================================
 RCS file: /usr/cvs/FreeBSD-CVS/src/sys/boot/i386/boot0/boot0.S,v
 retrieving revision 1.12
 diff -u -w -r1.12 boot0.S
 --- boot0.S	24 Nov 2004 15:39:04 -0000	1.12
 +++ boot0.S	5 Jan 2005 20:44:32 -0000
 @@ -29,7 +29,7 @@
  		.set PRT_OFF,0x1be		# Partition table
  
  		.set TBL0SZ,0x3 		# Table 0 size
 -		.set TBL1SZ,0xb 		# Table 1 size
 +		.set TBL1SZ,0xc 		# Table 1 size
  
  		.set MAGIC,0xaa55		# Magic: bootable
  		.set B0MAGIC,0xbb66		# Identification
 @@ -148,13 +148,8 @@
  		movb $TBL1SZ,%cl		# Number of entries
  		repne				# Known
  		scasb				#  type?
 -		jne main.4			# No
 -/*
 - * If it matches get the matching element in the next array.  If it doesn't,
 - * we are already pointing at its first element which points to a "?".
 - */
 -		addw $TBL1SZ,%di		# Adjust
 -main.4:		movb (%di),%cl			# Partition
 +		addw $TBL1SZ - 1, %di		# Adjust
 +		movb (%di),%cl			# Partition
  		addw %cx,%di			#  description
  		callw putx			# Display it
  main.5:		incw %dx			# Next item
 @@ -314,8 +309,7 @@
  		cmpw $MAGIC,0x1fe(%bx)		# Bootable?
  		jne main.10			# No
  		pushw %si			# Save
 -		movw $crlf,%si			# Leave some
 -		callw puts			#  space
 +		callw putn			# Leave some space
  		popw %si			# Restore
  		jmp *%bx			# Invoke bootstrap
  
 @@ -408,14 +402,14 @@
  		.byte 0x0, 0x5, 0xf
  /*
   * These values indicate bootable types we know the names of.
 + * The value of the last entry is unimportant: it indicates "everything else"
   */
  		.byte 0x1, 0x4, 0x6, 0xb, 0xc, 0xe, 0x83
 -		.byte 0x9f, 0xa5, 0xa6, 0xa9
 +		.byte 0x9f, 0xa5, 0xa6, 0xa9, 0xff
  /*
   * These are offsets that match the known names above and point to the strings
   * that will be printed.
   */
 -		.byte os_misc-. 		# Unknown
  		.byte os_dos-.			# DOS
  		.byte os_dos-.			# DOS
  		.byte os_dos-.			# DOS
 @@ -427,6 +421,7 @@
  		.byte os_freebsd-.		# FreeBSD
  		.byte os_bsd-.			# OpenBSD
  		.byte os_bsd-.			# NetBSD
 +		.byte os_misc-. 		# Unknown
  /*
   * And here are the strings themselves. 0x80 or'd into a byte indicates
   * the end of the string. (not so great for Russians but...)
 
 --------------070200040205060401080901--