[PATCH] m68k: Fix seccomp filtering on ColdFire and 68000

[Christopher Lusk <clusk@northecho.dev>]

m68k selects HAVE_ARCH_SECCOMP_FILTER for all configurations, but the
ColdFire and 68000 syscall entry paths only branch to
syscall_trace_enter() for TIF_SYSCALL_TRACE. TIF_SECCOMP alone falls
through to syscall dispatch, leaving installed filters ineffective.

Test TIF_SECCOMP in both paths and route it through the existing slow
path, matching the classic MMU syscall entry implementation.

Validated under QEMU mcf5208evb (ColdFire): a task installing a seccomp
filter denying getpid() still executed the syscall before this change and
returns -EPERM with it; likewise for a filter denying
openat/unlinkat/reboot. A classic-MMU control (q800) denied the filtered
syscall both before and after, confirming the gap is specific to the
ColdFire/68000 entry paths. The 68000 path shares the same source-level
omission and receives the identical fix but was not separately emulated.
Compile-tested W=1 with CONFIG_SECCOMP_FILTER=y on m5208evb_defconfig.

Fixes: 6baaade15594 ("m68k: Add kernel seccomp support")
Cc: stable@vger.kernel.org # v6.3+
Assisted-by: Claude:claude-opus-4-8
Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Christopher Lusk <clusk@northecho.dev>
---

Notes:
    No in-tree m68k defconfig selects the pure-68000/DragonBall path.
    Compile-tested W=1 with a custom no-MMU UCSIMM configuration and
    CONFIG_SECCOMP_FILTER=y; arch/m68k/68000/entry.o and vmlinux both built
    successfully. The added gate is form-identical to the ColdFire and
    classic-MMU gates.

 arch/m68k/68000/entry.S    | 2 ++
 arch/m68k/coldfire/entry.S | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/arch/m68k/68000/entry.S b/arch/m68k/68000/entry.S
index c257cc415..093be0a66 100644
--- a/arch/m68k/68000/entry.S
+++ b/arch/m68k/68000/entry.S
@@ -81,6 +81,8 @@ ENTRY(system_call)
 	getthreadinfo
 	btst	#(TIF_SYSCALL_TRACE%8),%a2@(TINFO_FLAGS+(31-TIF_SYSCALL_TRACE)/8)
 	jne	do_trace
+	btst	#(TIF_SECCOMP%8),%a2@(TINFO_FLAGS+(31-TIF_SECCOMP)/8)
+	jne	do_trace
 	cmpl	#NR_syscalls,%d0
 	jcc	badsys
 	lsl	#2,%d0
diff --git a/arch/m68k/coldfire/entry.S b/arch/m68k/coldfire/entry.S
index 4ea08336e..b73de9585 100644
--- a/arch/m68k/coldfire/entry.S
+++ b/arch/m68k/coldfire/entry.S
@@ -74,6 +74,8 @@ ENTRY(system_call)
 	movel	%sp,%a1@(TASK_THREAD+THREAD_ESP0)
 	btst	#(TIF_SYSCALL_TRACE%8),%a0@(TINFO_FLAGS+(31-TIF_SYSCALL_TRACE)/8)
 	bnes	1f
+	btst	#(TIF_SECCOMP%8),%a0@(TINFO_FLAGS+(31-TIF_SECCOMP)/8)
+	bnes	1f
 
 	movel	%d3,%a0
 	jbsr	%a0@
-- 
2.55.0