[JoachimSchipper]

Even as an OpenBSD fan, I'm not sure why tptacek was downvoted here. W^X etc. make it harder to write an exploit, but sufficiently-bad bugs can still yield arbitrary code execution. (Or confused-deputy problems allowing escalation to root, etc.; there's more than one way to pwn a box.)

And - architecturally - OpenBSD's kernel isn't that different from Linux, both being UNIX-style kernels; to the extent that OpenBSD's kernel has better security than Linux, it's mostly because OpenBSD tends to have fewer (and, sometimes, better-considered) features.

(There's an interesting argument to be had about Linux+grsecurity vs. OpenBSD - focusing on having some cutting-edge parts vs. solid engineering throughout - but that's not the argument we're having.)

[PhantomGremlin]

I'm not sure why tptacek was downvoted here

Maybe because his comment had the tone of:

"For this, I have found a truly wonderful proof, but the margin is too small to contain it."

[tptacek]

Do you need a "truly wonderful proof" for "the mainstream OS OpenBSD has not managed to render kernel vulnerabilities unexploitable, or to rid itself of those vulnerabilities entirely"? Because: that's an extraordinary claim for an OpenBSD supporter to make.

[PhantomGremlin]

I was not responding to "the mainstream OS OpenBSD ...". Let's go back to your remark, which preceded his:

kernel exploits for OpenBSD are neither theoretical nor impractical.

You put that out there as a bare, standalone statement. No elaboration, no proof.

Your comment might be true, but I would have liked to see some more "meat" in it. Some supporting evidence, some inkling of a truly wonderful proof.

[aortega]

I did write a remote kernel exploit for OpenBSD, it was not an easy task, and this was in a time when there were basically no exploit countermeasures in kernel (2007) (https://www.coresecurity.com/content/open-bsd-advisorie)

There are a bunch of local kernel exploits, all very practical and reliable. Kernel protections are something OpenBSD lacked until very recently.

[PhantomGremlin]

Yes, thanks for reminding me of that one.

That timeline isn't pretty. The OpenBSD guys really needed to be dragged, kicking and screaming, to calling it a "security fix" rather than something milder like a "reliability fix".