INTEL L1 TERMINAL FAULT

Intel_logoToday, Intel has confirmed a new vulnerability, Forestadow. There are three variants, one of which has a dangerous score of 7.9. It is a high-risk vulnerability. Intel and Microsoft are currently patching patches, and AMD processors have once again escaped.

  • CVE-2018-3615
  • CVE-2018-3620
  • CVE-2018-3646

It seems that our dislike of hyperthreading has finally been vindicated. We prefer real full cores which are far easier to use with OpenMP etc.

When a program attempts to access data in memory, the logical memory address is translated to a physical address by the hardware. Accessing a logical or linear address that is not mapped to a physical location on the hardware will result in a terminal fault.

Once the fault is triggered, there is a gap before resolution where the processor will use speculative execution to try to load data. During this time, the processor could speculatively access the level 1 data cache , potentially allowing side-channel methods to infer information that would otherwise be protected.

Microsoft has released some fixes which simply call the cache flush instruction bypassing the problem at the expense of performance Microsoft will have to fix the compiler’s to get around the problem permanently with a microcode fix.

Intel has a press release on the problem.

https://software.intel.com/security-software-guidance/software-guidance/l1-terminal-fault

Microsoft has a more indepth report.

https://blogs.technet.microsoft.com/srd/2018/08/14/analysis-and-mitigation-of-l1-terminal-fault-l1tf/