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| author | Mounir IDRASSI <mounir.idrassi@idrix.fr> | 2018-12-02 06:02:42 +0100 |
|---|---|---|
| committer | Mounir IDRASSI <mounir.idrassi@idrix.fr> | 2018-12-03 00:51:08 +0100 |
| commit | 3e1460b61895dc35adb86d36390f3c8722b1f90b (patch) | |
| tree | 6411f1212a5ed286120f358d06d58bdac33f8439 | |
| parent | e0049f601aca32e4dd5278d3ebe70d4e031e742f (diff) | |
| download | VeraCrypt-3e1460b61895dc35adb86d36390f3c8722b1f90b.tar.gz VeraCrypt-3e1460b61895dc35adb86d36390f3c8722b1f90b.zip | |
MBR Bootloader: dynamically determine boot loader memory segment instead of hardcoded values (proposed by neos6464 at https://sourceforge.net/p/veracrypt/tickets/240/)
| -rw-r--r-- | src/Boot/Windows/BootSector.asm | 31 |
1 files changed, 16 insertions, 15 deletions
diff --git a/src/Boot/Windows/BootSector.asm b/src/Boot/Windows/BootSector.asm index 33674146..351b2c67 100644 --- a/src/Boot/Windows/BootSector.asm +++ b/src/Boot/Windows/BootSector.asm @@ -43,23 +43,24 @@ main: call print skip_loader_name_msg: - ; Determine boot loader segment - mov ax, TC_BOOT_LOADER_SEGMENT - - ; Check available memory - cmp word ptr [ds:413h], TC_BOOT_LOADER_SEGMENT / 1024 * 16 + TC_BOOT_MEMORY_REQUIRED - jge memory_ok - - mov ax, TC_BOOT_LOADER_SEGMENT_LOW - - cmp word ptr [ds:413h], TC_BOOT_LOADER_SEGMENT_LOW / 1024 * 16 + TC_BOOT_MEMORY_REQUIRED - jge memory_ok - - ; Insufficient memory - mov ax, TC_BOOT_LOADER_LOWMEM_SEGMENT + ; Determine boot loader segment + mov ax, word ptr [ds:413h] ;available kB from BIOS + sub ax, TC_BOOT_MEMORY_REQUIRED ;minus TC_BOOT_MEMORY_REQUIRED + jc mem_toolow + and ax, 0FFE0h ;32K align + shl ax, 6 ;convert kB to segment addr (*1024/16) + cmp ax, 8000h + jb mem_toolow ;we can't load below 8000h + cmp ax, TC_BOOT_LOADER_SEGMENT + jbe memory_ok ;don't load above TC_BOOT_LOADER_SEGMENT (9000h) + mov ax, TC_BOOT_LOADER_SEGMENT + jmp memory_ok + +mem_toolow: + mov ax, TC_BOOT_LOADER_LOWMEM_SEGMENT memory_ok: - mov es, ax + mov es, ax ; Clear BSS section xor al, al |