[Mesa-dev] [PATCH] RFC: Workaround for pthread_setaffinity_np() seccomp filtering
marcandre.lureau at gmail.com
Thu Feb 28 16:13:34 UTC 2019
(ex-colleagues, long time ago!)
On Thu, Feb 28, 2019 at 1:37 PM Eero Tamminen <eero.t.tamminen at intel.com> wrote:
> On 28.2.2019 11.57, Marc-André Lureau wrote:
> > On Thu, Feb 28, 2019 at 1:17 AM Marek Olšák <maraeo at gmail.com> wrote:
> >> I'd rather have something more robust than an env var, like catching SIGSYS.
> SIGSYS is info for the invoking parent, not the (Mesa) process doing the
> From "man 2 seccomp":
> The process terminates as though killed by a SIGSYS signal. Even if a
> signal handler has been registered for SIGSYS, the handler will be
> ignored in this case and the process always terminates. To a parent
> process that is waiting on this process (using waitpid(2) or similar),
> the returned wstatus will indicate that its child was terminated as
> though by a SIGSYS signal.
> > With current qemu in most distros, it defaults to SIGSYS (we switched
> > away from SCMP_ACT_KILL, which had other problems). With more recent
> > qemu/libseccomp, it will default to SCMP_ACT_KILL_PROCESS. In those
> > KILL action cases, mesa will not be able to catch the failing
> > syscalls.
> Qemu / libvirt isn't the only thing using seccomp.
> For example Docker enables seccomp filters (along with capability
> restrictions) for the invoked containers unless that is explicitly
> What actually gets filtered, is trivially changeable on Docker command
> line by giving a JSON file specifying the syscall filtering.
> Default policy seems to be white-listing affinity syscall:
> Why distro versions of Qemu filter sched_setaffinity() syscall?
Daniel Berrange (berrange) wrote on 2019-02-27: #19
"IMHO that mesa change is not valid. It is settings its affinity to
run on all threads which is definitely *NOT* something we want to be
allowed. Management applications want to control which CPUs QEMU runs
on, and as such Mesa should honour the CPU placement that the QEMU
This is a great example of why QEMU wants to use seccomp to block
affinity changes to prevent something silently trying to use more CPUs
than are assigned to this QEMU."
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