Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Wed, 31 Oct 2018 10:45:06 +0100
From: Peter Zijlstra <>
To: Andy Lutomirski <>
Cc: Igor Stoppa <>,
	Matthew Wilcox <>,
	Tycho Andersen <>, Kees Cook <>,
	Mimi Zohar <>,
	Dave Chinner <>,
	James Morris <>, Michal Hocko <>,
	Kernel Hardening <>,
	linux-integrity <>,
	linux-security-module <>,
	Igor Stoppa <>,
	Dave Hansen <>,
	Jonathan Corbet <>, Laura Abbott <>,
	Randy Dunlap <>,
	Mike Rapoport <>,
	"open list:DOCUMENTATION" <>,
	LKML <>,
	Thomas Gleixner <>
Subject: Re: [PATCH 10/17] prmem: documentation

On Tue, Oct 30, 2018 at 02:02:12PM -0700, Andy Lutomirski wrote:
> But I dislike allowing regular writes in the protected region. We
> really only need four write primitives:
> 1. Just write one value.  Call at any time (except NMI).
> 2. Just copy some bytes. Same as (1) but any number of bytes.

Given the !preempt/!IRQ contraints I'd certainly put an upper limit on
the number of bytes there.

> 3,4: Same as 1 and 2 but must be called inside a special rare write
> region. This is purely an optimization.
> Actually getting a modifiable pointer should be disallowed for two
> reasons:
> 1. Some architectures may want to use a special
> write-different-address-space operation.

You're thinking of s390 ? :-)

> Heck, x86 could, too: make
> the actual offset be a secret and shove the offset into FSBASE or
> similar. Then %fs-prefixed writes would do the rare writes.

> 2. Alternatively, x86 could set the U bit. Then the actual writes
> would use the uaccess helpers, giving extra protection via SMAP.

Cute, and yes, something like that would be nice.

> We don’t really want a situation where an unchecked pointer in the
> rare write region completely defeats the mechanism.


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.