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

[Andy Lutomirski <luto@amacapital.net>]

On Wed, Oct 24, 2018 at 2:42 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Wed, Oct 24, 2018 at 1:40 PM, Palmer Dabbelt <palmer@sifive.com> wrote:
> > From: "Wesley W. Terpstra" <wesley@sifive.com>
> >
> > This is a fairly straight-forward implementation of seccomp for RISC-V
> > systems.
> >
> > Signed-off-by: Wesley W. Terpstra <wesley@sifive.com>
> > Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
> > ---
> >  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.

--Andy