Messages in this thread | | | Date | Tue, 14 Feb 2023 05:12:29 +0000 (GMT) | From | "Maciej W. Rozycki" <> | Subject | Re: [PATCH v3] x86: Use `get_random_u8' for kernel stack offset randomization |
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On Mon, 13 Feb 2023, Thomas Gleixner wrote:
> On Mon, Jan 30 2023 at 21:30, Maciej W. Rozycki wrote: > > > > Therefore switch to our generic entropy source and use `get_random_u8' > > instead, which according to Jason A. Donenfeld is supposed to be fast > > enough: > > > > "Generally it's very very fast, as most cases wind up being only a > > memcpy -- in this case, a single byte copy. So by and large it should > > be suitable. It's fast enough now that most networking things are able > > to use it. And lots of other places where you'd want really high > > performance. So I'd expect it's okay to use here too. And if it is too > > slow, we should figure out how to make it faster. But I don't suspect > > it'll be too slow." > > Please provide numbers on contemporary hardware.
Jason, is this something you could help me with to back up your claim?
My access to modern x86 gear is limited and I just don't have anything I can randomly fiddle with (I guess an Intel Core 2 Duo T5600 processor back from 2008 doesn't count as "contemporary", does it?).
> Up to that point, it's easy enough to just disable that randomization on > 32bit.
I think for 32-bit we could just go with `get_random_u8' unconditionally, but if you'd rather I disabled the feature altogether such as in v1 or v2, then I'm happy to resubmit whichever version seems the best, or make yet a different one. Please mind the security implications of RDTSC raised in the discussion though. Thanks for your feedback.
Maciej
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