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SubjectRe: x86 MSRs - example program
Matthias Urlichs wrote:
>
> In linux.dev.kernel, article <m0w1e9H-000AA6C@cerebro>,
> mlehmann@hildesheim.sgh-net.de (Marc Lehmann) writes:
> > >> ON the other hand... security hole????? how????????
> > >>
> > >Cryptography. If you know exactly how long a given algorithm takes for
> > >different inputs, you can sometimes infer clues about the secret key.
> >
> > gettimeofyday is always available, and in that scenario is just
> > as good as rdtsc.
> >
> gettimeofday isn't nearly as accurate. While that's not an absolute
> barrier, it raises the number of iterations required to get accurate data.

A few random length busy loops are enough to protect against a Kocher
attack. This is certainly not a reason to prevent ordinary users from
access to high resolution timers.

Best regards
Joerg
--
Joerg Pommnitz |Joerg@Raleigh.ibm.com| Never attribute to malloc
Mobile/Wireless |Dept UMRA | that which can be adequately
T/L (919)254-6397|Office B502/E117 | explained by stupidity.
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