Re: [PATCH 2/2] RISC-V: Add support for SECCOMP

[Palmer Dabbelt]

On Thu, 25 Oct 2018 14:02:20 PDT (-0700), luto@xxxxxxxxxxxxxx wrote:
> On Wed, Oct 24, 2018 at 2:42 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > On Wed, Oct 24, 2018 at 1:40 PM, Palmer Dabbelt <palmer@xxxxxxxxxx> wrote:
> > > From: "Wesley W. Terpstra" <wesley@xxxxxxxxxx>
> > >
> > > This is a fairly straight-forward implementation of seccomp for RISC-V
> > > systems.
> > >
> > > Signed-off-by: Wesley W. Terpstra <wesley@xxxxxxxxxx>
> > > Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxx>
> > > ---
> > >  arch/riscv/Kconfig                   | 18 ++++++++++++++++++
> > >  arch/riscv/include/asm/seccomp.h     | 10 ++++++++++
> > >  arch/riscv/include/asm/syscall.h     |  6 ++++++
> > >  arch/riscv/include/asm/thread_info.h |  1 +
> > >  include/uapi/linux/audit.h           |  1 +
> > >  5 files changed, 36 insertions(+)
> > >  create mode 100644 arch/riscv/include/asm/seccomp.h
> > >
> > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > index a344980287a5..28abe47602a1 100644
> > > --- a/arch/riscv/Kconfig
> > > +++ b/arch/riscv/Kconfig
> > > @@ -28,6 +28,7 @@ config RISCV
> > >         select GENERIC_STRNLEN_USER
> > >         select GENERIC_SMP_IDLE_THREAD
> > >         select GENERIC_ATOMIC64 if !64BIT || !RISCV_ISA_A
> > > +       select HAVE_ARCH_SECCOMP_FILTER
> >
> > I think this patch is missing most of the actual seccomp glue?
> >
> > config HAVE_ARCH_SECCOMP_FILTER
> >         bool
> >         help
> >           An arch should select this symbol if it provides all of these things:
> >           - syscall_get_arch()
> >           - syscall_get_arguments()
> >           - syscall_rollback()
> >           - syscall_set_return_value()
> >           - SIGSYS siginfo_t support
> >           - secure_computing is called from a ptrace_event()-safe context
> >           - secure_computing return value is checked and a return value of -1
> >             results in the system call being skipped immediately.
> >           - seccomp syscall wired up
> >
> > I only see syscall_get_arch(). Nothing is using TIF_SECCOMP (I'd
> > expect a masked check in entry.S -- it seems like tracepoints are
> > getting missed too? I see it handled in ptrace.c but not checked in
> > entry.S?) There's no checking for seccomp in ptrace.c, etc.
>
> Hi RISC-V people:
>
> I strongly, strongly suggest that you rewrite your asm to work the way
> that x86's does: have a function called prepare_exit_to_usermode() and
> make it work more or less like x86's.  Doing all the exit work in asm
> like you are is just setting you up for a world of pain.

OK, thanks for the suggestion.  Next time we have to change it I'll try to take 
a look and figure out something sane.