Messages in this thread | | | Date | Wed, 22 Feb 2023 12:05:19 +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 Tue, 14 Feb 2023, Jason A. Donenfeld wrote:
> > > 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?). > > I imagine tglx wants real life performance numbers rather than a > microbench of the rng. So the thing to do would be to exercise > arch_exit_to_user_mode() a bunch. Does this trigger on every syscall, > even invalid ones? If so, you could make a test like: > > #include <sys/syscall.h> > #include <unistd.h> > > int main(int argc, char *argv[]) > { > for (int i = 0; i < (1 << 26); ++i) > syscall(0xffffffff); > return 0; > } > > And then see if the timing changes across your patch.
Thanks. Though that does not solve my lack of suitable hardware, sigh. It's not like I have x86 systems scattered all over the place. I guess I could try to benchmark with said T5600 piece, but it won't be until April the earliest as I'm away most of the time.
Maciej
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