Re: [patch V2 05/10] MDS basics+ 5

On Thu, 21 Feb 2019, speck for Thomas Gleixner wrote:
>   2) What about BPF?
> 
>      If untrusted BPF can be abused to exploit this, then we have to think
>      hard about howto handle that.
> 
>      Assume the following:
> 
>      User A -> BPF -> preemption -> kernel thread -> back to BPF
> 
>      Because there is no kernel to user transition no buffer clear will
>      happen - neither in full nor in conditional mode.
> 
>      So the BPF sampler can happily collect the leftovers of the kernel
>      thread.
> 
>      Might be theoretical, but it needs to be investigated at least.

Just learned that BPF runs with preemption disabled. Oh well, yet another
thing which can't be used with Realtime systems. Well thought out.

Though the

       BPF -> interrupt -> softinterrupt -> BPF

scenario remains. It's not covered by full because it's not a user exit....

Thanks,

	tglx