Re: [RFC PATCH seccomp 1/2] seccomp/cache: Add "emulator" to check if filter is arg-dependent

[Jann Horn]

On Tue, Sep 22, 2020 at 1:44 AM YiFei Zhu <zhuyifei1999@xxxxxxxxx> wrote:
> On Mon, Sep 21, 2020 at 12:47 PM Jann Horn <jannh@xxxxxxxxxx> wrote:
> > > +       depends on SECCOMP
> > > +       depends on SECCOMP_FILTER
> >
> > SECCOMP_FILTER already depends on SECCOMP, so the "depends on SECCOMP"
> > line is unnecessary.
>
> The reason that this is here is because of the looks in menuconfig.
> SECCOMP is the direct previous entry, so if this depends on SECCOMP
> then the config would be indented. Is this looks not worth keeping or
> is there some better way to do this?

Ah, I didn't realize this.

> > > +       help
> > > +         Seccomp filters can potentially incur large overhead for each
> > > +         system call. This can alleviate some of the overhead.
> > > +
> > > +         If in doubt, select 'none'.
> >
> > This should not be in arch/x86. Other architectures, such as arm64,
> > should also be able to use this without extra work.
>
> In the initial RFC patch I only added to x86. I could add it to any
> arch that has seccomp filters. Though, I'm wondering, why is SECCOMP
> in the arch-specific Kconfigs?

Ugh, yeah, the existing code is already bad... as far as I can tell,
SECCOMP shouldn't be there, and instead the arch-specific Kconfig
should define something like HAVE_ARCH_SECCOMP and then arch/Kconfig
would define SECCOMP and let it depend on HAVE_ARCH_SECCOMP. It's
really gross how the SECCOMP config description has been copypasted
into a dozen different Kconfig files; and looking around a bit, you
can actually see that e.g. s390 has an utterly outdated help text
which still claims that seccomp is controlled via the ancient
"/proc/<pid>/seccomp". I guess this very nicely illustrates why
putting such options into arch-specific Kconfig is a bad idea. :P