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https://github.com/pbatard/rufus.git
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[mbr] various fixes and improvements
* Adds USB masquerading according to disk ID in USB part table * Adds debug feature * Closes #74 - was due to flags not being properly saved/restored * Closes #71 * Fixes reentrant INT_13h for some platforms (eg. IBM t43p reenters INT_13h to issue an SCSI passthrough, AH=0x50) * Embed MBR as a resource rather than an ms-sys header
This commit is contained in:
Pete Batard
parent
7874f5ea5d
commit
d87f069963
9 changed files with 80 additions and 112 deletions
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@ -1,5 +1,5 @@
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/********************************************************************************/
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/* Rufus - The Reliable USB Formatting Utility, bootable USB MBR */
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/* Rufus - The Reliable USB Formatting Utility, bootable MBR with user prompt */
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/* */
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/* Copyright (c) 2012 Pete Batard <pete@akeo.ie> */
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/* */
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@ -39,6 +39,7 @@ PT_MAX = 0x04 # Number of partition entries in the partition table
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PT_ENTRY_SIZE = 0x10 # Size of a partition entry in the partition table
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INT_RTC = 0x08
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INT_DSK = 0x13
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DEBUG = 0 # Set to 1 to debug INT13h (shows AH and DL values)
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/********************************************************************************/
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@ -82,10 +83,9 @@ mbr:
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# From this point forward, we are running the copy at the same base but different segment
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0: mov ds, ax # AX = ES = CS, only DS points back to old seg => fix this
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push 0
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pop es # ES remains set to segment 0 from here on
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xor ebx, ebx # Sector #1 in 64 bit address mode (#0)
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mov cx, 0x0001 # Sector #1 in CHS address mode (#1)
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mov es, bx # ES remains set to segment 0 from here on
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inc cx # Sector #1 in CHS address mode (#1) (and CX = 0 from rep movsb)
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mov dx, 0x0081 # drive number (DL), track 0 (DH)
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call read_sector
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jb boot_usb # If we couldn't get data => just boot USB
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@ -123,7 +123,7 @@ wait_for_keyboard:
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and al, 0x04 # AL = shift status bits
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jnz boot_usb
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cmpb ds:counter_dot, 0x00
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jg short check_timeout
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jg check_timeout
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print_dot: # Every so often, we print a dot
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mov si, offset dot_string
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@ -136,14 +136,17 @@ check_timeout:
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boot_fixed_disk: # Timeout occured => boot second bootable disk (non USB)
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call restore_rtc_vect # Remove our RTC override
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mov dx, offset dsk_interrupt # Set interrupt override to have
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mov si, offset dsk_interrupt_org # disk 0x81 is seen as 0x80
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call set_int_vect
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movb ds:partition_table, 0x81 # target we want to swap with 0x80
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push 0x0080
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boot_drive:
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mov dx, offset dsk_interrupt # Set interrupt override for int13h
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mov si, offset dsk_interrupt_org
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call set_int_vect
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pop dx # retrieve disk index to feed BR
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pop es
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pop ds
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mov dx, 0x0080 # In both case, we pretend the disk is the first bootable
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jmp 0:MBR_ADDR
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# ---------------------------------------------------------------------------
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@ -154,13 +157,13 @@ boot_usb:
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call flush_keyboard # Make sure the keyboard buffer is clear
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mov bx, offset partition_table
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mov dx, ds:[bx]
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push dx
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mov dl, 0x80 # Override disk number, as we're not using our int yet
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mov cx, ds:[bx+2]
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mov ebx, ds:[bx+8] # Must come last since it modifies BX
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call read_sector
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jnb boot_drive
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exit: # failed to read PBR from USB - exit back to BIOS
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pop es
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pop es # failed to read PBR from USB - exit back to BIOS
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pop ds
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retf
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@ -215,7 +218,7 @@ no_ext: # http://en.wikipedia.org/wiki/INT_13H#INT_13h_AH.3D02h:_Read_Sectors_Fr
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set_int_vect: # Set the interrupt vector
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cli # SI = pointer to backup vector (must contain the interrupt #)
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mov bx, ds:[si]
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mov eax, es:[bx] # Backup the original vector
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mov eax, es:[bx] # Backup the original vector (ES = 0)
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mov ds:[si], eax
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mov es:[bx], dx
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mov es:[bx+2], cs
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@ -257,21 +260,26 @@ print_string: # Print NUL terminated string in DS:SI to console
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# ---------------------------------------------------------------------------
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disk_swap: # Swap disks 0x80 and 0x81
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push dx
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and dl, 0xfe
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disk_swap: # Swap disk according to part table entry
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push ax
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mov al, cs:partition_table
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cmp dl, 0x80
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pop dx
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jne 0f
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xor dl, 0x01
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0: ret
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mov dl, al # 0x80 -> cs:pt
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jmp 1f
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0: cmp dl, al # cs:pt -> 0x80
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jne 1f
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mov dl, 0x80
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1: pop ax
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ret
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# ---------------------------------------------------------------------------
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.if 0
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print_hex: # Hex dump of the word at address ES:BX
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.if DEBUG
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print_hex: # Hex dump of AH,DL
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pusha
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mov cx, 0x04
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mov dx, es:[bx]
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mov dh, ah
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0: rol dx, 0x04
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mov ax, 0xe0f
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and al, dl
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@ -280,6 +288,7 @@ print_hex: # Hex dump of the word at address ES:BX
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adc al, 0x40
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int 0x10
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loop 0b
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popa
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ret
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.endif
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@ -290,44 +299,56 @@ print_hex: # Hex dump of the word at address ES:BX
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# RTC (INT 8) interrupt override
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rtc_interrupt:
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pushf
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cli
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cmpb cs:counter_timeout, 0x00
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jz rtc_exec_org
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jz 0f # Don't decrement counters if timeout expired
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decb cs:counter_dot
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decb cs:counter_timeout
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rtc_exec_org:
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rtc_interrupt_org = .+1 # Same trick used by the LILO mapper
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call 0:INT_RTC*4 # These CS:IP values will be changed at runtime
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iret
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0: jmp 0:INT_RTC*4 # These CS:IP values will be changed at runtime
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# ---------------------------------------------------------------------------
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# DISK (INT 13h) interrupt override
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dsk_interrupt:
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pushf
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cli
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.if DEBUG
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call print_hex
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.endif
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# Some machines (eg. IBM T43p) have a BIOS that reenters INT 13h to issue
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# an SCSI passthrough (AH = 50h). Therefore swapping the drive on each call
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# would result in failure. To ensure that the disk is only swapped once
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# we keep a counter, and swap only if that counter is 0.
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# NB: If concurrent INT 13h calls are issued, this approach will break
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incb cs:already_mapped
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jnz 0f
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call disk_swap
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dsk_interrupt_org = .+1
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call 0:INT_DSK*4 # These CS:IP values will be changed at runtime
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0: call 0:INT_DSK*4 # These CS:IP values will be changed at runtime
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# NB: subcommands 0x08 and 0x15 (disk props) modify DL, but they only
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# do so to return the number of drives => unless your computer has 128
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# or 129 drives, disk_swap will not touch those values.
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# do so to return the number of drives => unless your computer has more
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# than 128 drives, disk_swap will not touch those values.
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pushf # Don't modify the returned flags
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decb cs:already_mapped
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jns 0f
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call disk_swap
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popf
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iret
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0: popf
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retf 2
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/********************************************************************************/
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/* Data section */
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/********************************************************************************/
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already_mapped: .byte 0xff
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counter_timeout:.byte DOT_NUMBER*DOT_TIMEOUT + 1
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counter_dot: .byte DOT_TIMEOUT
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.if !DEBUG
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prompt_string: .string "\r\nPress any key to boot from USB."
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.else
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prompt_string: .string "USB."
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.endif
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dot_string = .-2 # Reuse the end of previous string
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