On Wed 2018-01-03 15:51:35, Linus Torvalds wrote: > On Wed, Jan 3, 2018 at 3:09 PM, Andi Kleen <a...@firstfloor.org> wrote: > > This is a fix for Variant 2 in > > https://googleprojectzero.blogspot.com/2018/01/reading-privileged-memory-with-side.html > > > > Any speculative indirect calls in the kernel can be tricked > > to execute any kernel code, which may allow side channel > > attacks that can leak arbitrary kernel data. > > Why is this all done without any configuration options? > > A *competent* CPU engineer would fix this by making sure speculation > doesn't happen across protection domains. Maybe even a L1 I$ that is > keyed by CPL.
Would that be enough?
AFAICT this will be pretty tricky to fix; it looks like you could
"attack" one userland application from another. Probing does not have
to work on L1 cache level; even main memory has "state".
It seems that complete fix would be considering any cache modification
and any memory access as a "side effect" -- so not okay to do
speculatively.
But that sounds... quite expensive for the performance...?
Pavel
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