OpenBSD Releases Meltdown Patch (theregister.co.uk)

OpenBSD's Meltdown patch has landed, in the form of a Version 11 code update that separates user memory pages from the kernel's -- pretty much the same approach as was taken in the Linux kernel. From a report: A few days after the Meltdown/Spectre bugs emerged in January, OpenBSD's Phillip Guenther responded to user concerns with a post saying the operating system's developers were working out what to do. Now he's revealed the approach used to fix the free OS: "When a syscall, trap, or interrupt takes a CPU from userspace to kernel the trampoline code switches page tables, switches stacks to the thread's real kernel stack, then copies over the necessary bits from the trampoline stack. On return to userspace the opposite occurs: recreate the iretq frame on the trampoline stack, switch stack, switch page tables, and return to userspace." That explanation is somewhat obscure to non-developers, but there's a more readable discussion of what the project's developers had in mind from January, here.

Comments

Are we so sure it does not affect AMD?

[SuperKendall]

I have nothing against AMD, and in general support competition for Intel...

But are we truly sure the Meltdown approach cannot work on AMD? From all of the reading I did doing the Meltdown fiasco, it seemed like the people who came up with Meltdown thought it might work on AMD, they could just not get the timing to work quite right in a proof of concept attack the way they could with Intel...

Is there a more detailed technical description laying out exactly why AMD processors are for sure immune to the Meltdown attack? It seemed that with something that affected so many different processors, it's strange that only AMD escaped.