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

Kees Cook
2018-10-24T21:42:03Z

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.

At the very least, I think the Kconfigs should not be included in this
patch. The other things are needed, but without everything else,
seccomp isn't actually available. :)

Reading the per-arch Kconfigs, I am reminded I still need to move
CONFIG_SECCOMP up into arch/Kconfig. :P

-Kees

--
Kees Cook