Messages in this thread | | | Subject | Re: Hyper-Threading Vulnerability | From | Lee Revell <> | Date | Sat, 14 May 2005 03:37:18 -0400 |
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On Fri, 2005-05-13 at 19:44 -0400, Dave Jones wrote: > On Fri, May 13, 2005 at 07:38:08PM -0400, Lee Revell wrote: > > On Fri, 2005-05-13 at 19:27 -0400, Dave Jones wrote: > > > 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. > > > > > > > Well yes but you would still have to recompile those apps. > > Not if the app is written correctly. See above.
The apps that bother to use rdtsc vs. gettimeofday need a cheap high res timer more than a correct one anyway - it's not guaranteed that rdtsc provides a reliable time source at all, due to SMP and frequency scaling issues.
I'll try to benchmark the difference. Maybe it's not that big a deal.
Lee
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