Questions tagged [bios]

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1answer
42 views

Flash ROM has lower max voltage than read device?

I'm planning to read a MX25U1635E chip using the CH341a reader. The specs for that chip say it has a max voltage of 1.6-2.0 volts. The reader has an output of 3.3-5.0 volts. Most tutorials for the ...
3
votes
1answer
124 views

Undocumented MSR Machine Specific register

I'm reversing the BIOS of my laptop, for fun and for learning something new. Inside it, I just stepped into this piece of code: mov ecx, 13Ah rdmsr and eax, 1 jnz SkipCacheAsRAM Looking ...
5
votes
1answer
71 views

Passing a (string) argument via the return address?

I'm debugging an old PC BIOS and it has most of its constant strings interspersed directly with the code, like this: As the comment notes, the function putsc will take the string as its argument, ...
2
votes
1answer
97 views

Why are these 0-byte jumps used as a delay?

I'm debugging an old PC BIOS and see a lot of what I assume are delay sequences, using 0-byte jump instructions (EB 00 = jmp short $+2). Why this particular instruction? I'm guessing it must have ...
2
votes
1answer
846 views

Reverse Engineering BIOS (AMI A0.57)

Recently I got really interested in BIOS RE and I used chipsec to dump the content of SPI Flash ROM of my HP Omen Desktop PC to start my journey. But unlike older BIOSes, the binary file was pretty ...
1
vote
3answers
399 views

Decompress and Analyse VMWARE EFI64 bios

I want to analyse this UEFI bios here. When I open it in IDA it looks compressed to me. Also IDA lists the processor type as ZLOG. Shouldn't this be the multi processor setting for IDA? Anyway, If I ...
3
votes
1answer
115 views

Why BIOS is not asking for HDD password on reboot but only after power off?

I was reading about BIOS and I saw this: Next, BIOS will begin checking memory at 0000:0472h. This address contains a flag which will tell the BIOS if the system is booting from a cold boot or warm ...
1
vote
1answer
480 views

Find changes between two UEFI firmware versions?

I have saved a copy of the UEFI firmware currently running on my motherboard through the built-in flash utility. Now I want to compare the firmware dump with the newest firmware update from the ...
0
votes
1answer
104 views

BIOS code failed to check device and run into a infinite loop

I'm hacking a thinkpad BIOS to remove the card whitelist. I run the bios firmware in qemu and debug with IDApro. .\qemu-system-x86_64.exe -m 4096M -bios D:\W25Q32BV\old.bin -s -S But, the code run ...
14
votes
1answer
4k views

How can BIOS routines be disassemblied?

There was once a disassembler on DOS named Sourcer that can disassembly BIOS routines. However, how do we access to BIOS ROM from software to do such a thing?
4
votes
1answer
1k views

How Can I Debug A Bios Better

I am trying to reverse engineer a firmkit in a bios, but in general I would like to know how can I debug a bios better. I found a way to attach IDA to a vmware instance usign a GDB session GDB ...
17
votes
2answers
4k views

In which language is the BIOS written?

As I understand, the BIOS code/bitstream that held in the ROM should be generic (work alongside with multiple CPU types or ISAs). In addition, I saw mentions in the web that claim to have the ...