Questions tagged [x86-64]

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MSVC Generates Weird Code for Volatile Local Variable

I want to know how MSVC 2010 generates code for volatile local variable and have done a test. This simple test function uses a volatile local variable: int proc1(int a, int b) { int volatile ...
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1answer
415 views

IDA Pro 64bit offset and opcode issue

I'm looking at a 64bit PE file in IDA. The instructions below access unknown data at offset 20030. Usually when I look at 32bit PE files, the offset is also listed next to the opcodes on the left. So ...
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1answer
527 views

brute force remote nop sled memory address

ELF x64 binary on a remote server communicates via simple socket server in C. After overflowing the buffer (total buffer is 2000, password buffer is less), overwriting the RIP, filling with NOP sled (...
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1answer
167 views

What do square brackets do in IDA's pseudocode representation?

I've been a bit stumped recently on my decomp work. I've not dealt with C in depth nor have I dealt with IDA's pseudocode system very much at all. I understand asm, but because of how IDA merges ...
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1answer
193 views

How do I go about overriding a function internally defined in a binary on Linux?

To be specific, I cannot recompile this binary, nor do I have access to the sourcecode. The functions are not defined within a shared library. So, how can I go about changing a function, or ...
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1answer
180 views

How to locate an specific data structure in an executable?

I need to locate an specific "struct" variable in the data section from an assembly. This structure is used for an specific System Function (Windows) "SetCommState()". I'm wondering how to locate the ...
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1answer
296 views

x64 Linux reverse-engineering - understanding asm code and inject eax

In a rootme exercise, i'm trying to bypass the control impleted to protect a "read" function. You'll find enclosed the code i'm refering to. As you may understand, i can inject data (with limitations) ...
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1answer
90 views

How can I modify these?

So I'm onto something interesting, I asked the less direct way but failed to meet the requirements in terms of explanation So here it is, how would I go about editing these the same way I would go ...
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1answer
98 views

How to determine when/where pointers in .ctors get mapped?

So I am learning about ELF, and am looking through a binary in Ghidra as I do. I've made sense of the ELF header, and now I am looking through the program header table. My binary has a bunch of ...
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1answer
161 views

XCHG RAX, RAX: 0x03, what does this code do and how does it work?

"XCHG RAX, RAX" is a kind of riddle book that provides assembly code for you to reverse and undercover the meaning. Some of the examples calculate the Fibonacci sequence others bit-twiddle to toggle ...
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1answer
69 views

Reading params of a text engine function amd86_64

I'm starting to learn amd86_64 calling convention and how it calls params and clean the stack but the concept hasn't sunk in yet, so i would like to get a help reading the params as this might clear ...
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2answers
78 views

Magic number in resource loading routine

I'm practicing windows disassembly on x64 notepad.exe I've managed to find buffer allocation and string resources load. But after that follows code, which I can't fully understand: rbx = 0, rdx = 0 ...
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1answer
730 views

Linux x64 Disassembly: single movzwl operand question

A quick question regarding a movzwl instruction which do not behave as I expected. here is the disassembled code: movzwl (%rax),%eax Before the instruction, rax is 0x7fffffffe410 and point to 0x5 ...
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2answers
863 views

Trying to call a function in an unknown DLL

My goal is far from nefarious. After several polite attempts to try and get Lenovo to implement a proper keyboard backlight control, I've had no response. They do have a Windows Store app which adds ...
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1answer
128 views

Why is using a 32bit system over 64bit recommended for people that are new to reverse engineering? [closed]

I am new to the world of reverse engineering and have been recommended by a number of people that I should start with IA32 because it is easier to learn the concepts. Aside from differences in the ...
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1answer
1k views

Calling DLL exports in x64dbg

I am attempting to debug a x64bit dll with x64dbg. Is there an export caller similar to Ollydbg? I checked the documents and haven't seen anything.
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1answer
54 views

Cant recognise where is my targeted function executed

Im trying to recognise where is my targeted function int64 __fastcall sub_1400CE4F0(__int64 a1, const char *a2)executed. When stepping through this function, after return it's redirecting me here: if (...
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43 views

Change value of memory in a debugger?

So I got this app loaded in x64, there is a function, let's say "HeatGainedPerShot", which is basically the value which an object gains everytime it fires, Such a value would normally exist ...
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30 views

Windows pintool mismatch between call/ret instructions

So i've been trying to write a pintool that monitors call/ret instructions but i've noticed that threre was a significant inconsistency between the two. For example ret instructions without previous ...
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0answers
48 views

What does the file pointer of fgets actually point to in linux?

So i was reversing a 64 bit ELF binary, and it did a call to fgets, and based on documentation the third argument of fgets is a file pointer. now the weird part was that the third argument in this ...
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40 views

Extra Allocated Space in Stack and Wrong placement of Local Variable

I was recently reading reverse engineering for beginners by Yurichev where I happened to come across an example x64 MSVC and x64 GCC code. In this I'm unable to understand why there is a shadow space ...
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70 views

Why does this execve shellcode work with this argv?

I wrote the following program in fasm, and am using Evan's Debugger on Ubuntu to debug it: format ELF64 executable 3 segment readable executable entry $ mov rbp, rsp sub rsp, 32 mov rax, 'this a t' ...
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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 ...
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66 views

Bufferoverflow Stack

I want to do a buffer overflow exploit in the stack. For this i read in data via the "gets"-function. void ExploitMe() { char buffer[256]; gets(buffer); } I compile this file with gcc test.c -...
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134 views

R13 off by 2 bytes. Any help?

in this challenge i have to overwrite RIP register to point to the function "print_flags" which calls "getenv" to get the "FLAGS" variable. I have overwritten RIP register with the address of "...
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1answer
134 views

Calculate LEA operand

I have those opcodes on 64 bits: 48 8D 35 45 CE FF FF >>> lea rsi, [rip - 0x31bb]. How can I get the 0x31bb value from those opcodes and how can I know if I have a + sign or a - sign ...
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2answers
2k views

How can I use an x64 debugger to reroute a .NET application's logic?

I'd like to improve my reverse engineering skills, so I made this WPF application (targeting x64, of course): MainWindow.xaml: <Window x:Class="ApplicationTest.MainWindow" xmlns="http://...
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1answer
61 views

What does xchg means when accessing array element?

I have ASM code of some Windows *.exe in IDA: mov rax, [rbx+10h] mov ecx, edx xor edx, edx xchg rdx, [rax+rcx*8] Which is decompiled to pseudocode to _RAX = this->m_someMemoryPool; ...

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