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

[Geert Uytterhoeven <geert@linux-m68k.org>]

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>
> ---
>  arch/m68k/Kconfig                   |  2 ++
>  arch/m68k/include/asm/seccomp.h     | 11 +++++++++++
>  arch/m68k/include/asm/syscall.h     | 33 +++++++++++++++++++++++++++++++++
>  arch/m68k/include/asm/thread_info.h |  2 ++
>  arch/m68k/kernel/ptrace.c           |  5 +++++
>  5 files changed, 53 insertions(+)
>  create mode 100644 arch/m68k/include/asm/seccomp.h
>
> diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
> index 372e4e6..deaea88 100644
> --- a/arch/m68k/Kconfig
> +++ b/arch/m68k/Kconfig
> @@ -19,6 +19,8 @@ config M68K
>         select GENERIC_STRNCPY_FROM_USER if MMU
>         select GENERIC_STRNLEN_USER if MMU
>         select HAVE_AOUT if MMU
> +       select HAVE_ARCH_SECCOMP
> +       select HAVE_ARCH_SECCOMP_FILTER

So the status should be changed from "TODO" to "ok" in
Documentation/features/seccomp/seccomp-filter/arch-support.txt

BTW, there was also "[PATCH] [WIP] selftests/seccomp: Add m68k support"
https://lore.kernel.org/linux-m68k/alpine.DEB.2.21.2008261315050.25325@ramsan.of.borg/

I kept on up-porting it, but haven't exercised it recently.
Recent version looks like (gmail-whitespace-damaged):

--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -135,6 +135,8 @@ struct seccomp_data {
 #  define __NR_seccomp 337
 # elif defined(__sh__)
 #  define __NR_seccomp 372
+# elif defined(__mc68000__)
+#  define __NR_seccomp 380
 # else
 #  warning "seccomp syscall number unknown for this architecture"
 #  define __NR_seccomp 0xffff
@@ -1815,6 +1817,10 @@ TEST_F(TRACE_poke, getpid_runs_normally)
 # define ARCH_REGS             struct pt_regs
 # define SYSCALL_NUM(_regs)    (_regs).regs[3]
 # define SYSCALL_RET(_regs)    (_regs).regs[0]
+#elif defined(__mc68000__)
+# define ARCH_REGS             struct pt_regs
+# define SYSCALL_NUM(_regs)    (_regs).orig_d0
+# define SYSCALL_RET(_regs)    (_regs).d0
 #else
 # error "Do not know how to find your architecture's registers and syscalls"
 #endif
@@ -1879,7 +1885,7 @@ const bool ptrace_entry_set_syscall_ret =
  * Use PTRACE_GETREGS and PTRACE_SETREGS when available. This is useful for
  * architectures without HAVE_ARCH_TRACEHOOK (e.g. User-mode Linux).
  */
-#if defined(__x86_64__) || defined(__i386__) || defined(__mips__)
+#if defined(__x86_64__) || defined(__i386__) || defined(__mips__) ||
defined(__mc68000)
 # define ARCH_GETREGS(_regs)   ptrace(PTRACE_GETREGS, tracee, 0, &(_regs))
 # define ARCH_SETREGS(_regs)   ptrace(PTRACE_SETREGS, tracee, 0, &(_regs))
 #else

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