[Xenomai] SMAP-detected direct userspace access

Jan Kiszka jan.kiszka at web.de
Sun Dec 27 18:42:41 CET 2015


On 2015-12-27 18:41, Gilles Chanteperdrix wrote:
> On Sun, Dec 27, 2015 at 06:00:02PM +0100, Jan Kiszka wrote:
>> 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.
> 
> The ABI overhaul should happen in the 3.1 branch, hopefully real
> soon now (tm).
> 

Cool!

Jan

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