Questions tagged [bios]

BIOS (basic input/output system) is a special program to get the computer system started after you turn it on.

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18
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 ...
14
votes
1answer
5k 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?
5
votes
1answer
81 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, ...
4
votes
1answer
268 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 ...
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 ...
3
votes
1answer
133 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 ...
2
votes
2answers
120 views

BIOS first jump leads to empty memory

I'm trying to reverse a BIOS of an industrial PC in order to repair it. The device is based on an ETX-formfactor mobo, obscure Italian SECO M671, very similar to an old Kontron PM-15(C), but with a ...
2
votes
1answer
119 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
89 views

Undocumented Model-Specific Register on Broadwell Microarchitecture

I'm trying to reverse the BIOS of a machine to learn something. The bigger problem I'm facing is that during early initialization, the code is making heavy usage of MSRs, and most of the time, I found ...
2
votes
1answer
1k 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
1k views

Reverse Engineering a Binary to reset a BIOS password

I have a laptop that I recently lost the BIOS Admin password for. I contacted the manufacturer and, after giving them some information about my BIOS (version, uuid), they sent me a file, smc.bin to ...
1
vote
3answers
951 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 ...
1
vote
1answer
72 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 ...
1
vote
1answer
937 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 ...
1
vote
0answers
56 views

Removing/bypassing a BIOS whitelist

I am trying to bypass or erase the BIOS whitelist on my Thinkpad T440p. So far I've used flashrom and a soic8 clip to dump the bios to a bios.img file made another dump and compared with diff bios....
1
vote
0answers
107 views

removing bios wireless white listing

I am trying to remove the white listing for wireless cards from my Thinkpad L540 running Debian Buster. I did the following steps: booted with kernel parameter iomem=relaxed used pawn to dump BIOS ...
0
votes
1answer
117 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 ...
0
votes
0answers
21 views

CPU integrated PCI device functions

I'm trying to reverse an Xeon based hardware bios. During the early initialization in the UEFI SEC phase, I stepped into some CPU embedded PCI devices initialization. After few hours researches, I've ...