GSoC 2018 Reports: Kernel Address Sanitizer, Part 1

Prepared by Siddharth Muralee (@Tr3x__) as part of GSoC 2018.

It's been a fun couple of weeks since I started working on the Kernel Address Sanitizer (KASan) project with NetBSD. I have learned a lot during this period. It's been pretty amazing. This is a report on the work I have done prior to the first evaluation period.

What is an Address Sanitizer?

The Address Sanitizer (ASan) is an open source tool that was developed by Google to detect memory corruption bugs such as buffer overflows or access to dangling pointers (use after free). Its a part of the toolset that Google has which includes an Undefined Behaviour Sanitizer (UBSan), a Thread Sanitizer (TSan) and a Leak Sanitizer (LSan).

On adding the feature to NetBSD it would be possible to add build the kernel with ASan and then use it to find memory corruption bugs.

Testing ASan in the User Space

My first step was to testing whether ASan had been implemented in the NetBSD userspace. I wrote a couple of ATF regression tests for checking whether ASan worked in the userspace for C and C++ compilers and also whether manual poisoning would work.

This allowed me to get familiar with the ATF testing framework that NetBSD.

Added a couple of Kernel Modules

I was asked to add a set of example kernel modules to the kernel. I added an example module to show how to make a /dev module multiprocessor safe and to add a node in the sysctl tree.

Reading about UVM

My next task was to get familiar with the UVM (virtual memory system of NetBSD). I read through a 1998 dissertation by Dr. Chuck Cranor. I published a blog article containing my scratch notes on reading the article.

Adding an option to compile the kernel with KASan

Finally, I had to build the kernel with the KASan stubs (Dummy functions so that the build would be working). I added a configuration file which can be used to build the kernel with KASAN. I also published a blog post regarding how to do the same.

Summary

In short, I am pretty excited to move forward with the project. The community has been supportive and helpful all the way.

I would like to thank my mentor, Kamil Rytarowski who was always ready to dive deep into code and help whenever required. I also want to thank Cherry Mathews for helping clear up doubts related to UVM. [0 comments]