Seems like the real question is how does it work on a z13?  2048-4095
(x'800-FFF') are *supposed* to be key0 fetch-protected.

"Fetch Protection Override" (CR0:38) is to allow everyone to fetch from
0-2047 (x'0-7FF'), while leaving 2048-4095 fetch protection in effect.  It
is not a new feature, nor is it a "legacy" thing.  IBM hasn't deprecated
the common CVT pointer.

It's documented in PoOp: SA22-7832-12 page 3-13.

sas


On Wed, Aug 19, 2020 at 4:16 PM Binyamin Dissen <[email protected]>
wrote:

> Fetch-protection-override (cr0.38) allowed the OS to put fetch protection
> on
> page0 while allowing (legacy) access to 0-2047.
>
> Don't know which hardware level allowed exploitation.
>
>

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