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References: <5674331B.2010807@siemens.com>
From: Philippe Gerum <rpm@xenomai.org>
Message-ID: <56743641.6080908@xenomai.org>
Date: Fri, 18 Dec 2015 17:37:21 +0100
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Subject: Re: [Xenomai] SMAP-detected direct userspace access
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To: Jan Kiszka <jan.kiszka@siemens.com>, Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
Cc: Xenomai <xenomai@xenomai.org>

On 12/18/2015 05:23 PM, Jan Kiszka wrote:
> Hi all,
> 
> I know this is legacy code, but this is where we currently stumbled into
> it, and maybe the same pattern also exists in 3.x:
> 
> http://git.xenomai.org/xenomai-2.6.git/tree/ksrc/skins/posix/syscall.c#n1182
> 
> more precisely:
> 
>     return pse51_mutex_check_init(&umx->shadow_mutex, attr);
> 
> Here we pass the userspace object for initialization to the core instead
> of handing over the kernel shadow and then copying over the result. Is
> there a reason for this? Could we have more of such cases?
> 
> Background: SMAP detects and prevents any direct userspace memory access
> on x86 except or those that are wrapped in stac() and clac() (which
> toggle a bit in eflags). Generally a useful feature we should allow to
> be enabled for robustness reasons.
> 

As far as 3.x is concerned, I don't think this direct access pattern is
used there, this would have likely caused me some headaches for
supporting the 32/64 mixed ABI models, and I don't remember of any such
headache. At any rate, I don't see any reason to do this in 3.x.

-- 
Philippe.