Questions tagged [x86-64]

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38 views

How can I connect basic blocks seperated by unconditional jmps?

I'm analyzing an obfuscated code which splits its code into multiple blocks seperated by many, many unconditional jmps. Here is a picture of what the obfuscation looks like: I wrote an IDAPython ...
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1answer
196 views

How can i check if i am running in ring 0 / ring 3 on x64 CPU

I have read it is possible to check ring level with bit 3 of CS register. Is there another register which really contains ring value (2 bits)
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2answers
399 views

PE32+ executable : .text segment encryption

I am working on PE segment encryption(in C++). I completed the PE32 .text segment encryption. I added stub segment to the PE that will decrypt .text segment at runtime. Used inline assembly in the ...
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1answer
106 views

startup program exits with code 126 when executing program at entrypoint

I want to reverse engineer a program. I managed to find the entry point but every time I want to launch the application I get the same error `During startup program exited with code 126. Here is what ...
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1answer
398 views

How can I get the inferred register value for an instruction in Ghidra scripting?

I'd like to get the inferred value of a register at a particular point in the disassembly listing in a Ghidra script. In my case the target instruction is a rdmsr or wrmsr instruction, which reads or ...
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0answers
25 views

Why PTRACE_POKEDATA returns I/O error?

I learning usage of ptrace. I tried following simple example but raises a I/O Error. I would like to overwrite "Hello, world" (printing string) from other process. A target program prints &...
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45 views

Trying to call the Exit Shellcode in a c program

#include<stdio.h> #include<stdint.h> char shellcode[] = "\xb8\x3c\x00\x00\x00" "\xbf\x14\x00\x00\x00" "\x0f\x05"; int ...
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1answer
57 views

Disassembly call function offset from RIP

I am writing a program where I map an .exe PE file in memory and I "dissect" it. I am disassembling the .text section of the target executable, using the distorm disassembler. CALL ...
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1answer
55 views

does mov DWORD PTR 32[rsp], 5 means mov DWORD PTR [rsp+32], 5?

I am learning about windows x64 calling convention, where the first four arguments are passed to registers and left arguments are passed through the stack. To see it, I checked the assembly of the ...
2
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1answer
6k views

Receiving “Got EOF while reading in interactive” after properly executing system(“/bin/sh”) using pwntools

I've followed some tutorials on writing a pwntools-based exploit for the bitterman ELF binary, used in a CTF competition. However, all my attempts fail with the message below, i.e. Got EOF while ...
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2answers
7k views

How many registers does an x86_64 CPU actually have?

I am currently learning reverse engineering and am studying the flags register. I had in my mind that rflags was just another name for one of the 16 general purpose registers, for example rax or rbx. ...
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4answers
3k views

What is the difference between MOV and LEA in example?

Looking at an assembly code snippet I see: lea rax, [rbp-0x50] Which tells me that the rax register now points to whatever value is in rbp-hex(50). Question. Would I achieve the same result doing ...
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31 views

objdump says “64-bit address is disabled”

I've run into an issue with the MinGW build of objdump on Windows. Consider this very simple input file: 48 bf 88 77 66 55 44 33 22 11 I want to disassemble this as Intel x86-64 raw machine code. I ...
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3answers
83k views

How to obtain x86-64 pseudocode in IDA Pro?

Does anyone know about obtaining pseudocode for x86-64 in IDA Pro? I already tried the Hex-Rays plugin to obtain pseudocode, but when I try it, the following error pops up: "only 32bit code is ...
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1answer
83 views

Calling MessageBoxW x64 confused about pointer

OK, I am very new to x64dbg. I used to use OllyDbg a lot and I'm having some problems with this. I just made a customized version of MS-PAINT for practice by changing a few things like the default ...
2
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1answer
143 views

x64dbg or alternative: Run to selection while storing all ran opcodes

I'm trying to trace a function, but unfortunately that function is huge and has lots and lots of jumps to other locations, making it almost impossible to trace for humans. I know the entry point and ...
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40 views

Remapping Branch Instructions After Obfuscation

Recently I've been working on a project. I've already got a hint for a problem that I had here: (Garbage Assembly Code Generationat at random offsets) however, the accepted answer's solution doesn't ...
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0answers
32 views

Instruction-level hooking library for win32?

I am looking for instruction-level hooking library for win32 x86/x64. I want to write hook insertion and hook implementation code in C/C++ (compiled into dll). (Therefore instrumentation tools are ...
2
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1answer
86 views

Garbage Assembly Code Generationat at random offsets

Recently I've been working on a project. The main purpose of the project is to generated statically undetectable PE samples. Where each time one generates a PE sample, each generated sample is going ...
2
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1answer
44 views

Difference in binary behaviour (execution/under debugger)

I was trying out a simple heap overflow example (http://highaltitudehacks.com/2020/09/05/arm64-reversing-and-exploitation-part-1-arm-instruction-set-heap-overflow/) but replicated the relevant code in ...
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1answer
101 views

Help understanding x64 TEST instruction

I have read that TEST does a bitwise and on the two arguments. I have also read that jz and je are both equivalent, and jump if the zero flag is set. So here's the problem I'm struggling with. ...
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1answer
72 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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2answers
404 views

how to does this instruction work: `mov qword ptr [rbp-0x30], 0x4020c5`

The following is the code snippet (shown partially) I have: q = strrchr(resolved, '/'); /* given /home/misha/docs.txt, q now pts to the last slash */ if (q != NULL) { p = q + 1; ...
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1answer
60 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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1answer
570 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 (...
3
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1answer
129 views

Radare2 - what does dot mean in disassembly

I've just started using radare2 and I've noticed a dot when I tried to disassamble one on my programs. The output is: 0x00000000 48b841000000. movabs rax, 0x41 I understand that 0x48 is the REX ...
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1answer
95 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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0answers
47 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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0answers
38 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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2answers
90 views

Where do arguments 5 and 6 go in this Microsoft x64 function call?

I'm disassembling a working-as-expected compiled C program (MS/Windows x64, MinGW gcc 10.1.0). In the main function, I have the following call which passes 6 arguments to the function DotProduct: ... /...
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1answer
62 views

Displaying Operands as Position Independent in IDA

I'm writing an IDA python script, and i need to be able to detect position independent code. I have an instruction that IDA displays using the operand name 'format' lea rdi, format However, when ...
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1answer
107 views

Is `movq rax, xmm0` buggy in Radare2?

Why doesn't rax get loaded from xmm0 here? radare2 bug? GitHub issue `movq rax, xmm0` doesn't work in native debugger filed. [0x0003b0e0]> drr role reg value ref ―――――――――――――――――――...
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3answers
1k views

Elf x86_64 adding function

I'm trying to see if I can append function code in the .text section of an ELF while still maintaining the execution flow of the original ELF. Ideally, I want to call the new function but that's it's ...
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2answers
92 views

x64 processor module

I just downloaded Ghidra last evening on a Fedora Linux machine with 4 Intel Core i5-7200U CPUs. When querying the "installed processor modules" in "Help" I get a listing of 41 processors. x86 is on ...
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1answer
477 views

Help understanding MOVSXD

I've tried reading the documentation but the functionality of this instruction is still cloudy to me. For an example, I would like to know what is stored in RDX after these instructions: mov edx, ...
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0answers
41 views

Memory modified at jump far

Observing a trace of Wow64 switching on Windows 7, the following situation makes me confused ... 0x77491dbe 64 ff 15 c0 00 00 00 call fs:[0xc0] ; syswow64\ntdll.dll 0x74632320 ea 1e 27 63 ...
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1answer
47 views

How to determine what code created a string, in a live debugger session?

I'm using IDA 7 to debug a running application that must be a child of another application, which means I can't start it from IDA (using Debugger->Run). Instead, I have to run the application normally,...
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1answer
34k views

What does mov qword ptr ds:[rax+18], r8 mean?

mov qword ptr ds:[rax+18], r8 In the above code, where are we copying the value of r8 register into? I know that ds means data segment which is a segment in memory, but what does exactly [rax+18] ...
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1answer
92 views

Finding “func main” in a stripped binary written in GO

I'm reversing a binary that was apart of a CTF I was involved in about a month ago. It was too large of a binary to do during the challenge so I am doing it now. I am having trouble finding the main ...
2
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1answer
915 views

Windbg: How to directly view GS:[0x60]

Win10x64: In Windbg, how may I view a pointer to the PEB by directly using GS:[0x60] (and not by Windbg extensions)? To test, I assembled a program via masm64 that throws an interrupt, clears r8 then ...
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1answer
69 views

Isolate the call to a function

Is it possible to call a function of a binary and obtain its result (without calling other functions), to isolate; are there any tools to do this?
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1answer
617 views

cannot find a string in x64dbg even when using search all strings

I am trying to debug a program for testing but for some reason i can NOT find any strings related to registeration like Registered, Unregistered,Blocked in x64dbg, i can see all these strings in the ...
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0answers
30 views

Go back to the original entry point after executing the instructions in the newly added segment- PE32+, C++

I am learning PE32+ (64 bit) files. I have added a new section to the PE32+ file and made the new section as the entry point. Some simple instructions are added in the new segment. Now I want to go to ...
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1answer
146 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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0answers
149 views

How to interpret binary instruction using the intel manual

OK. So I am really trying to figure out how to use the "Intel 64 and IA-32 Architectures Software Developer's Manual" for myself, since it seems like the authoritative source for x86(_64) machine code....
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1answer
327 views

Why address 7FFE0308 always gets compared in 64bit applications before making a syscall in Ntdll?

So there was a question asked before about this : What are the difference syscall and int 0x2E instructions? and it has two answer, one says that is just a way to check if we are in a 32 bit or 64 ...
2
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1answer
153 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 ...
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1answer
318 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 ...
2
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1answer
163 views

How to hide a process from all the methods of getting the list of processes?

So it seems that there are a lot of ways of getting the process list, although I'm not sure whether in the low level do they acquire them from same place or not so these are the ways i know : ...
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3answers
2k views

How to find the starting address of text section of a DLL inside a process? (64 bit)

There was a question about this a year ago, but the answer doesn't explain how to do it in C/C++: How to find start of .text section? I'm not talking about module start address, which we can get ...