Mark Johnston
Senior Software Engineer at Klara Inc
Old Toronto, Ontario, Canada
Summary
🤩
Rockstar🎓
Top SchoolMark Johnston is a Senior Software Engineer with 14 years of deep systems and OS-level expertise, primarily centered on FreeBSD development and ZFS. He is a long-standing FreeBSD src committer and consultant for organizations like Netflix and the FreeBSD Foundation, blending production engineering at companies such as Klara and Dell EMC with research work at the University of Cambridge on CheriBSD. Mark’s open-source impact includes porting syzkaller kernel fuzzing to FreeBSD and bhyve support and a steady stream of low-level ZFS fixes that improve reliability and memory safety. Comfortable across back-end, DevOps, and low-level systems programming, he focuses on correctness, performance, and maintainability rather than surface features. A Waterloo-educated developer, he brings a rare combination of academic research experience and hands-on platform hardening that surfaces in critical infrastructure projects.
14 years of coding experience
7 years of employment as a software developer
Bachelor of Mathematics, Computer Science and Pure Mathematics, Bachelor of Mathematics, Computer Science and Pure Mathematics at University of Waterloo
Github Skills (34)
filesystem10
openzfs10
system-programming10
package-management10
security-txt10
freebsd10
testing10
locking10
memory-management10
build-system10
c1110
security10
c1710
kernel10
package-manager-tool10
Programming languages (10)
Github contributions (5)
google/syzkaller
Mar 2019 - Jan 2023
syzkaller is an unsupervised coverage-guided kernel fuzzer
Role in this project:
Back-end Developer & DevOps Engineer
Back-end Developer & DevOps EngineerContributions:67 reviews, 87 commits, 90 PRs in 3 years 11 months
Contributions summary:Mark contributed to the FreeBSD support within the syzkaller project, a kernel fuzzer. Their work involved porting and adapting the build system, including kernel toolchain and image creation, to FreeBSD. They also modified existing code to accommodate FreeBSD-specific requirements, such as handling file flags and syscalls. Furthermore, the user added support for bhyve, FreeBSD's native hypervisor, and configured networking for it.
kernelsecurity-toolscoverage-guidedfuzz-testingsecurity
openzfs/zfs
Jun 2020 - Jan 2023
OpenZFS on Linux and FreeBSD
Role in this project:Back-end Developer
Back-end DeveloperContributions:17 reviews, 65 commits, 30 PRs in 2 years 7 months
Contributions summary:Mark primarily contributes to the ZFS codebase, focusing on low-level systems programming. Their commits involve bug fixes related to locking mechanisms, particularly in the FreeBSD implementation of ZFS. Furthermore, they address potential memory corruption issues by initializing various data structures and padding bytes. The user also works on improving the performance and reliability of the ZFS system by disabling hardware crypto offload and optimizing functions.
openzfstarballlinuxfreebsdsystem-software
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