Re: Hyper-Threading Vulnerability

Dave Jones
2005-05-13T23:30:22Z

On Fri, May 13, 2005 at 07:00:12PM -0400, Lee Revell wrote:
> On Fri, 2005-05-13 at 23:47 +0100, Alan Cox wrote:
> > On Gwe, 2005-05-13 at 22:59, Matt Mackall wrote:
> > > It might not be much of a problem though. If he's a bit off per guess
> > > (really impressive), he'll still be many bits off by the time there's
> > > enough entropy in the primary pool to reseed the secondary pool so he
> > > can check his guesswork.
> >
> > You can also disable the tsc to user space in the intel processors.
> > Thats something they anticipated as being neccessary in secure
> > environments long ago. This makes the attack much harder.
>
> And break the hundreds of apps that depend on rdtsc? Am I missing
> something?

If those apps depend on rdtsc being a) present, and b) working
without providing fallbacks, they're already broken.

There's a reason its displayed in /proc/cpuinfo's flags field,
and visible through cpuid. Apps should be testing for presence
before assuming features are present.

Dave