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

- From: Tycho Andersen \<hidden\>
- Date: 2018-02-14 22:13:28 
- List: linux-security-module
- Page: https://ratatoskr.run/linux-security-module/2018/02/5197653
- Thread: https://ratatoskr.run/linux-security-module/2018/01/5184248/t.md

```text
On Wed, Feb 14, 2018 at 11:48:38AM -0800, Kees Cook wrote:
> On Wed, Feb 14, 2018 at 11:06 AM, Laura Abbott [ref] 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
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