Re: [PATCH 4/7] x86: Add support for rd/wr fs/gs base

H. Peter Anvin
2014-04-30T04:57:59Z

On 04/29/2014 09:52 PM, H. Peter Anvin wrote:
>
> It matters -- greatly -- if (and only if) we can enter the kernel with
> usergs == kernelgs and then want to change usergs inside a paranoid
> routine. At that point we risk being upside down, which basically means
> we're rooted.
>
> However, I believe this patchset also means only IST entries can be
> paranoid, which in turn means we can't sleep inside them. To the very
> best of my knowledge the only times we change usergs is on context
> switch or inside a system call. We need to make sure that is actually
> the case, though.
>
> I'm at ELC for a few days, so I'll have limited decent-sized-monitor
> time, but it shouldn't be too hard to convince ourselves of... mostly a
> matter of making sure something like ptrace can't to stupid crap.
>

Just in case anyone is getting the wrong impression: this is a
discussion about details. I'm glad to see this work getting done.

-hpa