Re: arm64 physmap (was Re: [kernel-hardening] [PATCH 4/6] Protectable Memory)

[Kees Cook]

On Wed, Feb 14, 2018 at 11:06 AM, Laura Abbott <labbott@xxxxxxxxxx> wrote:
> fixed. Modules yes are not fully protected. The conclusion from past
> experience has been that we cannot safely break down larger page sizes
> at runtime like x86 does. We could theoretically
> add support for fixing up the alias if PAGE_POISONING is enabled but
> I don't know who would actually use that in production. Performance
> is very poor at that point.

XPFO forces 4K pages on the physmap[1] for similar reasons. I have no
doubt about performance changes, but I'd be curious to see real
numbers. Did anyone do benchmarks on just the huge/4K change? (Without
also the XPFO overhead?)

If this, XPFO, and PAGE_POISONING all need it, I think we have to
start a closer investigation. :)

-Kees

[1] http://www.openwall.com/lists/kernel-hardening/2017/09/07/13

-- 
Kees Cook
Pixel Security