linux-kernel - Re: [PATCH] CMA: Do no enable it by default

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Date:	Wed, 6 Jun 2012 14:59:29 +0200
From:	Borislav Petkov <bp@...64.org>
To:	Christopher Yeoh <cyeoh@....ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Randy Dunlap <rdunlap@...otime.net>
Subject: Re: [PATCH] CMA: Do no enable it by default

On Wed, Jun 06, 2012 at 10:54:59AM +0930, Christopher Yeoh wrote:
> > CROSS_MEMORY_ATTACH is a MPI feature which shouldn't be enabled by
> > default on every linux system simply because the majority of users do
> > not need it.
> 
> btw although CMA was primarily written for MPI it is used by more than
> just MPI implementations. For example, recent versions of strace now
> use it instead of PTRACE_PEEKDATA if its available:
> 
> http://article.gmane.org/gmane.comp.sysutils.strace.devel/2467/match=process_vm_readv

I see.

Looks like process_vm_readv() is faster than PTRACE_PEEKDATA. You
could add this to the config option text so people can know why they
could/should enable CMA.

Oh, and also the note about ptrace privileges below :-).

> > Besides, in the config option it says "... which allow a process with
> > the correct privileges to directly read from or write to to another
> > process's address space.", which, if the reading process has somehow
> > gained privileges (as that never happens) is your security issue right
> > there.
> 
> The privileges required are exactly the same as required to ptrace the
> target. You're rather stuffed anyway if you have a hostile process with
> those privileges.

Ok.

Thanks.

-- 
Regards/Gruss,
Boris.

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