[tor-bugs] #21010 [Applications/Tor Browser Sandbox]: Disable RDTSC/RDTSCP to limit side-channel attacks

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#21010: Disable RDTSC/RDTSCP to limit side-channel attacks
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 Reporter:  cypherpunks                       |          Owner:  yawning
     Type:  enhancement                       |         Status:  new
 Priority:  High                              |      Milestone:
Component:  Applications/Tor Browser Sandbox  |        Version:
 Severity:  Normal                            |     Resolution:
 Keywords:                                    |  Actual Points:
Parent ID:                                    |         Points:
 Reviewer:                                    |        Sponsor:
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Comment (by cypherpunks):

 A small correction on my part.

 >The reason this happens is that a few syscalls, namely `getcpu()`,
 `gettimeofday()`, `time()`, and `clock_gettime()` use the `RDTSC`
 instruction

 The `getcpu()` and `time()` vDSOs do not use `RDTSC`. I meant to say they
 were all vDSOs, but those two are safe to call even with TSC instructions
 restricted to ring 0. `getcpu()` uses `LSL` instead of `RDTSCP` (since it
 works on all architectures), and `time()` consults a dynamically updating
 value in the VVAR.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21010#comment:3>
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