Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions

[H. Peter Anvin]

Andi Kleen wrote:
> > Ok. CPU folks are planning to make some of the bytes at the end of fxsave
> > image, SW usable.
>
> Are they always zeroed in earlier CPUs though?  If not that wouldn't
> work 100% reliably because whatever cookie you put in could have been
> there before by chance.
>
> I don't see anything in the SDM guaranteeing zeroing.

I'm pretty sure they weren't zeroed by the CPUs.  If they weren't zeroed 
*by the kernel*, there might have been an information leak.

	-hpa
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