Messages in this thread | | | Date | Thu, 2 May 2019 18:43:25 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall |
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* Andy Lutomirski <luto@kernel.org> wrote:
> > 8 gigabits/sec sounds good throughput in principle, if there's no > > scalability pathologies with that. > > The latency is horrible.
Latency would be amortized via batching anyway, so 8 gigabits/sec suggests something on the order of magnitude of 4 bits per cycle, right? With 64 bits extraction at a time that would be 16 cycles per 64-bit word, which isn't too bad, is it?
But you are right that get_random_bytes() is probably faster, and also more generic.
> > It would also be nice to know whether RDRAND does buffering > > *internally*, > > Not in a useful way :(
Too bad ...
> > Any non-CPU source of randomness for system calls and plans to add > > several extra function calls to every x86 system call is crazy talk I > > believe... > > I think that, in practice, the only real downside to enabling this > thing will be the jitter in syscall times. Although we could decide > that the benefit is a bit dubious and the whole thing isn't worth it. > But it will definitely be optional.
Making it "optional" is not really a technical argument in any way though, either distros enable it in which case it's a de-facto default setting, or they don't, in which case it de-facto almost doesn't exist.
Thanks,
Ingo
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