[Xenomai] SMAP-detected direct userspace access

[Jan Kiszka <jan.kiszka@siemens.com>]

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.

Thanks,
Jan

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