Gallopsled/pwntools

`context.bits` will not automatically switch when setting `context.arch` twice.

Open

#2,498 opened on Nov 10, 2024

View on GitHub
 (3 comments) (0 reactions) (0 assignees)Python (11,127 stars) (1,684 forks)batch import
backport-requiredbuggood first issue

Description

I was using IPython to do some quick poc work that time, first I switched context.arch to 'amd64' and assembled cdqe and then I suddenly would like to try what if I assemble cdqe in 32-bit mode. So I switched context.arch back to 'i386' and wanted to assemble, only to find an error: AttributeError: Invalid arch/bits combination: i386/64

Pwntools may can not handle context.arch correctly, it could change context.bits accordingly when first setting it. However, when setting context.arch the second time, context.bits left unchanged. I guess this bug is related to self._tls?

poc:

屏幕截图_20241111_003054

one more poc:

from pwn import *
print(f"{context.arch}/{context.bits}")
context.arch = 'amd64'
print(f"{context.arch}/{context.bits}")
context.arch = 'i386'
print(f"{context.arch}/{context.bits}")

Contributor guide

Tech stack
python
Domain
tooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
familiarity with pwntools context systemPython debugging
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65
Research direction
Investigate how `context.arch` updates `context.bits` in the pwntools library. The bug likely resides in the context module, possibly in the ` tls` property or the arch setter. Review the code in `pwnlib/context/ init .py` or `pwnlib/context/context.py` to understand how arch changes affect bits. The fix should ensure that whenever `context.arch` changes, `context.bits` is updated accordingly, even on subsequent assignments.