linux-kernel - Re: [RESENT PATCH] x86/mem: fix the offset overflow when read/write mem

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 09 May 2017 11:46:43 -0400
From:   Rik van Riel <riel@...hat.com>
To:     zhong jiang <zhongjiang@...wei.com>
Cc:     David Rientjes <rientjes@...gle.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Andrew Morton <akpm@...ux-foundation.org>, arnd@...db.de,
        hannes@...xchg.org, kirill@...temov.name,
        mgorman@...hsingularity.net, hughd@...gle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Xishi Qiu <qiuxishi@...wei.com>
Subject: Re: [RESENT PATCH] x86/mem: fix the offset overflow when read/write
 mem

On Thu, 2017-05-04 at 10:28 +0800, zhong jiang wrote:
> On 2017/5/4 2:46, Rik van Riel wrote:

> > However, it is not as easy as simply checking the
> > end against __pa(high_memory). Some systems have
> > non-contiguous physical memory ranges, with gaps
> > of invalid addresses in-between.
> 
>  The invalid physical address means that it is used as
>  io mapped. not in system ram region. /dev/mem is not
>  access to them , is it right?

Not necessarily. Some systems simply have large
gaps in physical memory access. Their memory map
may look like this:

|MMMMMM|IO|MMMM|..................|MMMMMMMM|

Where M is memory, IO is IO space, and the
dots are simply a gap in physical address
space with no valid accesses at all.

> > At that point, is the complexity so much that it no
> > longer makes sense to try to protect against root
> > crashing the system?
> > 
> 
>  your suggestion is to let the issue along without any protection.
>  just root user know what they are doing.

Well, root already has other ways to crash the system.

Implementing validation on /dev/mem may make sense if
it can be done in a simple way, but may not be worth
it if it becomes too complex.

-- 
All rights reversed
Download attachment "signature.asc" of type "application/pgp-signature" (474 bytes)