[Info-vax] Intel junk...Kernel-memory-leaking Intel processor design flaw forces Linux, Windows redesign

[Johnny Billquist]

On 2018-01-06 19:23, Tim Streater wrote:
> In article <p2qtjk$ul0$1 at Iltempo.Update.UU.SE>, Johnny Billquist
> <bqt at softjar.se> wrote:
> 
>> And then they figured out a clever way of mining the contents of the 
>> cache.
>>
>> One could argue that the cache should be invalidated in such a 
>> scenario, but that is not happening either.
> 
> Never mind invalidating it. WTF is going on if a non-priv process has
> the right to do anything at all to the cache? Non-priv processes
> shouldn't even be aware that there *is* a cache, never mind having the
> right to execute instructions *about* the cache.

Normally, that is true. But clever people can do a lot around this.
When I was doing my CS major, we had a course on advanced computer 
architectures, in where we learned how to write a very simple program 
that told us everything about cache size, associativeness, line size, 
TLB size, TLB associativeness, and so on...
All you need to do is understand how the computer is affected by these 
things, and then write programs that detect the effects.

In short, you write small loops that exercise the cache in different 
ways, and time the whole thing. You don't even need any high precision 
timers for it. All user level, and all very simple.

Caches are not "visible" to normal operation, but caches affects the 
timing a *lot*. Which is obvious, since that is why the cache is there 
in the first place.

I assume you are not arguing that the cache should be disabled for user 
processes.

Any instruction that refers to memory is executing instructions that is 
about the cache.

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol