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

[Tycho Andersen]

On Wed, Feb 14, 2018 at 11:48:38AM -0800, Kees Cook wrote:
> 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. :)

I haven't but it shouldn't be too hard. What benchmarks are you
thinking?

Tycho