linux-kernel - Re: [PATCH RFC 01/15] uaccess: count pagefault_disable() levels in pagefault

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: <20150507132335.51016fe4@thinkpad-w530>
Date:	Thu, 7 May 2015 13:23:35 +0200
From:	David Hildenbrand <dahi@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com,
	yang.shi@...driver.com, bigeasy@...utronix.de,
	benh@...nel.crashing.org, paulus@...ba.org,
	akpm@...ux-foundation.org, heiko.carstens@...ibm.com,
	schwidefsky@...ibm.com, borntraeger@...ibm.com, mst@...hat.com,
	tglx@...utronix.de, David.Laight@...LAB.COM, hughd@...gle.com,
	hocko@...e.cz, ralf@...ux-mips.org, herbert@...dor.apana.org.au,
	linux@....linux.org.uk, airlied@...ux.ie, daniel.vetter@...el.com,
	linux-mm@...ck.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH RFC 01/15] uaccess: count pagefault_disable() levels in
 pagefault_disabled

> On Thu, May 07, 2015 at 12:50:53PM +0200, David Hildenbrand wrote:
> > Just to make sure we have a common understanding (as written in my cover
> > letter):
> > 
> > Your suggestion won't work with !CONFIG_PREEMPT (!CONFIG_PREEMPT_COUNT). If
> > there is no preempt counter, in_atomic() won't work. 
> 
> But there is, we _always_ have a preempt_count, and irq_enter() et al.
> _always_ increment the relevant bits.
> 
> The thread_info::preempt_count field it never under PREEMPT_COUNT
> include/asm-generic/preempt.h provides stuff regardless of
> PREEMPT_COUNT.
> 
> See how __irq_enter() -> preempt_count_add(HARDIRQ_OFFSET) ->
> __preempt_count_add() _always_ just works.
> 
> Its only things like preempt_disable() / preempt_enable() that get
> munged depending on PREEMPT_COUNT/PREEMPT.
> 

Sorry for the confusion. Sure, there is always the count.

My point is that preempt_disable() won't result in an in_atomic() == true
with !PREEMPT_COUNT, so I don't see any point in adding in to the pagefault
handlers. It is not reliable.


David

--
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/