Re: [PATCH v5 2/2] m68k: add kernel seccomp support

[Michael Schmitz <schmitzmic@gmail.com>]

Hi Geert, Andeas,
I admit I am no great shakes at libc stuff - how is syscall argument
no. 6 passed in the few syscalls that have this many arguments?
Cheers,
  Michael

On Wed, Jun 23, 2021 at 7:27 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
> Hi Michael,
>
> On Thu, Jun 17, 2021 at 7:39 AM Michael Schmitz <schmitzmic@gmail.com> wrote:
> > Add secure_computing() call to syscall_trace_enter to actually
> > filter system calls.
> >
> > Add necessary arch Kconfig options, define TIF_SECCOMP trace
> > flag and provide basic seccomp filter support in asm/syscall.h
> >
> > syscall_get_nr currently uses the syscall nr stored in orig_d0
> > because we change d0 to a default return code before starting a
> > syscall trace. This may be inconsistent with syscall_rollback
> > copying orig_d0 to d0 (which we never check upon return from
> > trace). We use d0 for the return code from syscall_trace_enter
> > in entry.S currently, and could perhaps expand that to store
> > a new syscall number returned by the seccomp filter before
> > executing the syscall. This clearly needs some discussion.
> >
> > Compiles (for Atari) and boots on ARAnyM, otherwise untested.
> >
> > Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
>
> Thanks for your patch!
>
> > --- a/arch/m68k/include/asm/syscall.h
> > +++ b/arch/m68k/include/asm/syscall.h
> > @@ -4,6 +4,39 @@
> >
> >  #include <uapi/linux/audit.h>
> >
> > +#include <asm/unistd.h>
> > +
> > +extern const unsigned long sys_call_table[];
> > +
> > +static inline int syscall_get_nr(struct task_struct *task,
> > +                                struct pt_regs *regs)
> > +{
> > +       return regs->orig_d0;
> > +}
> > +
> > +static inline void syscall_rollback(struct task_struct *task,
> > +                                   struct pt_regs *regs)
> > +{
> > +       regs->d0 = regs->orig_d0;
> > +}
> > +
> > +static inline void syscall_set_return_value(struct task_struct *task,
> > +                                           struct pt_regs *regs,
> > +                                           int error, long val)
> > +{
> > +       regs->d0 = (long) error ? error : val;
> > +}
> > +
> > +static inline void syscall_get_arguments(struct task_struct *task,
> > +                                        struct pt_regs *regs,
> > +                                        unsigned long *args)
> > +{
> > +       args[0] = regs->orig_d0;
> > +       args++;
> > +
> > +       memcpy(args, &regs->d0 + 1, 5 * sizeof(args[0]));
>
> This doesn't look right to me: "&regs->d0 + 1" is "&regs->orig_d0"
> again, and there are no registers after that.
> Perhaps you meant "&regs->d1"?
>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds