Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date: Wed, 21 Feb 2018 14:22:10 -0800
From: Kees Cook <>
To: Igor Stoppa <>
Cc: Laura Abbott <>, Jann Horn <>, 
	Boris Lukashev <>, Christopher Lameter <>, 
	Matthew Wilcox <>, Jerome Glisse <>, 
	Michal Hocko <>, Christoph Hellwig <>, 
	linux-security-module <>, Linux-MM <>, 
	kernel list <>, 
	Kernel Hardening <>, 
	linux-arm-kernel <>
Subject: Re: arm64 physmap (was Re: [PATCH 4/6] Protectable Memory)

On Tue, Feb 20, 2018 at 8:28 AM, Igor Stoppa <> wrote:
> On 14/02/18 21:29, Kees Cook wrote:
>> On Wed, Feb 14, 2018 at 11:06 AM, Laura Abbott <> wrote:
> [...]
>>> Kernel code should be fine, if it isn't that is a bug that should be
>>> fixed. Modules yes are not fully protected. The conclusion from past
>> I think that's a pretty serious problem: we can't have aliases with
>> mismatched permissions; this degrades a deterministic protection
>> (read-only) to a probabilistic protection (knowing where the alias of
>> a target is mapped). Having an attack be "needs some info leaks"
>> instead of "need execution control to change perms" is a much lower
>> bar, IMO.
> Why "need execution control to change permission"?
> Or, iow, what does it mean exactly?
> ROP/JOP? Data-oriented control flow hijack?

Right, I mean, if an attacker has already gained execute control, they
can just call the needed functions to change memory permissions. But
that isn't needed if there is a mismatch between physmap and virtmap:
i.e. they can write to the physmap without needing to change perms

> One can argue that this sort of R/W activity probably does require some
> form of execution control, but AFAIK, the only way to to prevent it, is
> to have CFI - btw, is there any standardization in that sense?

I meant that I don't want a difference in protection between physmap
and virtmap. I'd like to be able to reason the smae about the
exposures in either.

> So, from my (pessimistic?) perspective, the best that can be hoped for,
> is to make it much harder to figure out where the data is located.
> Virtual mapping has this side effect, compared to linear mapping.

Right, this is good, for sure. No complaints there at all. It's why I
think pmalloc and arm64 physmap perms are separate issues.


Kees Cook
Pixel Security

Powered by blists - more mailing lists

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.