[Xenomai] SMAP-detected direct userspace access

Jan Kiszka jan.kiszka at web.de
Sun Dec 27 18:00:02 CET 2015


On 2015-12-18 18:12, Gilles Chanteperdrix wrote:
> On Fri, Dec 18, 2015 at 05:23:55PM +0100, 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.
> 
> BTW, I believe most RTnet ioctls have this issue.
> 

Correct, long-pending deficit that will now start to bite back more
seriously. I was always postponing this until some potential userspace
ABI overhaul.

Jan

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