From: anton@nospicedham.mips.complang.tuwien.ac.at   
      
   Terje Mathisen  writes:   
   >Meltdown depends on having a cache that is shared among multiple   
   >threads/processes, so that you have a covert channel which allows you to   
   >detect what supposedly secure code is doing.   
      
   Actually Meltdown is the attack that allows a user process to read   
   kernel memory, if the kernel is mapped (but unreadable) in the user   
   process.  It does not depend on sharing of the caches between   
   processes.  The process reads the kernel memory speculatively, and   
   some CPUs (e.g., most Intel CPUs) actually continue speculatively with   
   the result, eventuelly squashing the whole path; but the side effect   
   on the caches is observable and can be exploited to extract the kernel   
   data into the user process.   
      
   - anton   
   --   
   M. Anton Ertl                    Some things have to be seen to be believed   
   anton@mips.complang.tuwien.ac.at Most things have to be believed to be seen   
   http://www.complang.tuwien.ac.at/anton/home.html   
      
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