linux-kernel - Re: [PATCH v8 08/10] x86, mpx: add prctl commands PR_MPX_REGISTER, PR_MPX

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]

Message-ID: <alpine.DEB.2.10.1409121120440.4178@nanos>
Date:	Fri, 12 Sep 2014 11:24:49 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dave Hansen <dave.hansen@...el.com>
cc:	Qiaowei Ren <qiaowei.ren@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 08/10] x86, mpx: add prctl commands PR_MPX_REGISTER,
 PR_MPX_UNREGISTER

On Fri, 12 Sep 2014, Thomas Gleixner wrote:
> On Thu, 11 Sep 2014, Dave Hansen wrote:
> > Well, we use it to figure out whether we _potentially_ need to tear down
> > an VM_MPX-flagged area.  There's no guarantee that there will be one.
> 
> So what you are saying is, that if user space sets the pointer to NULL
> via the unregister prctl, kernel can safely ignore vmas which have the
> VM_MPX flag set. I really can't follow that logic.
>  
> 	mmap_mpx();
> 	prctl(enable mpx);
> 	do lots of crap which uses mpx;
> 	prctl(disable mpx);
> 
> So after that point the previous use of MPX is irrelevant, just
> because we set a pointer to NULL? Does it just look like crap because
> I do not get the big picture how all of this is supposed to work?

do_bounds() will happily map new BTs no matter whether the prctl was
invoked or not. So what's the value of the prctl at all?

The mapping is flagged VM_MPX. Why is this not sufficient?

Thanks,

	tglx

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/