m68k: Add kernel seccomp support

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.

seccomp_bpf self test on ARAnyM passes 81 out of 94 tests.

Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20230112035529.13521-3-schmitzmic@gmail.com
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

1 files changed, 57 insertions, 0 deletions

diff --git a/arch/m68k/include/asm/syscall.h b/arch/m68k/include/asm/syscall.h
index 465ac039be09..d1453e850cdd 100644
--- a/arch/m68k/include/asm/syscall.h
+++ b/arch/m68k/include/asm/syscall.h
@@ -4,6 +4,63 @@
 
 #include <uapi/linux/audit.h>
 
+#include <asm/unistd.h>
+
+extern const unsigned long sys_call_table[];
+
+static inline int syscall_get_nr(struct task_struct *task,
+				 struct pt_regs *regs)
+{
+	return regs->orig_d0;
+}
+
+static inline void syscall_rollback(struct task_struct *task,
+				    struct pt_regs *regs)
+{
+	regs->d0 = regs->orig_d0;
+}
+
+static inline long syscall_get_error(struct task_struct *task,
+				     struct pt_regs *regs)
+{
+	unsigned long error = regs->d0;
+
+	return IS_ERR_VALUE(error) ? error : 0;
+}
+
+static inline long syscall_get_return_value(struct task_struct *task,
+					    struct pt_regs *regs)
+{
+	return regs->d0;
+}
+
+static inline void syscall_set_return_value(struct task_struct *task,
+					    struct pt_regs *regs,
+					    int error, long val)
+{
+	regs->d0 = (long)error ?: val;
+}
+
+static inline void syscall_get_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 unsigned long *args)
+{
+	args[0] = regs->orig_d0;
+	args++;
+
+	memcpy(args, &regs->d1, 5 * sizeof(args[0]));
+}
+
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 unsigned long *args)
+{
+	regs->orig_d0 = args[0];
+	args++;
+
+	memcpy(&regs->d1, args, 5 * sizeof(args[0]));
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	return AUDIT_ARCH_M68K;