Fwd: A more general possible meltdown/spectre countermeasure
Wojciech Puchar
wojtek at puchar.net
Sat Jan 6 20:42:04 UTC 2018
> The only workaround that's completely effective is to unmap all of kernel memory when running in userland. It's a bit tricky because
this means on every syscall on interrupt:
- memcopy part of top level PTE on enter, bzero on exit
- TLB flush both on enter and exit.
IMHO it would make much more than 30% overhead in many cases. am i wrong?
> there's small parts that have to stay mapped for various architectural reasons. This means KASLR on these CPUs likely can never be
> effective since meltdown will let you find what the trap address is and from that find the kernel (though there's some rumblings
> that the indirection Linux is doing will suffice).
>
> Warner
>
>
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