[PATCH RFC] m68k: add kernel seccomp support

[Michael Schmitz <schmitzmic@gmail.com>]

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
 	select HAVE_ASM_MODVERSIONS
 	select HAVE_DEBUG_BUGVERBOSE
 	select HAVE_FUTEX_CMPXCHG if MMU && FUTEX
diff --git a/arch/m68k/include/asm/seccomp.h b/arch/m68k/include/asm/seccomp.h
new file mode 100644
index 0000000..de8a94e
--- /dev/null
+++ b/arch/m68k/include/asm/seccomp.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _ASM_SECCOMP_H
+#define _ASM_SECCOMP_H
+
+#include <asm-generic/seccomp.h>
+
+#define SECCOMP_ARCH_NATIVE		AUDIT_ARCH_M68K
+#define SECCOMP_ARCH_NATIVE_NR		NR_syscalls
+#define SECCOMP_ARCH_NATIVE_NAME	"m68k"
+
+#endif /* _ASM_SECCOMP_H */
diff --git a/arch/m68k/include/asm/syscall.h b/arch/m68k/include/asm/syscall.h
index 465ac03..87bf69f 100644
--- a/arch/m68k/include/asm/syscall.h
+++ b/arch/m68k/include/asm/syscall.h
@@ -4,6 +4,39 @@
 
 #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 void syscall_set_return_value(struct task_struct *task,
+					    struct pt_regs *regs,
+					    int error, long val)
+{
+	regs->d0 = (long) error ? 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->d0 + 1, 5 * sizeof(args[0]));
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	return AUDIT_ARCH_M68K;
diff --git a/arch/m68k/include/asm/thread_info.h b/arch/m68k/include/asm/thread_info.h
index 15a7570..d813fed 100644
--- a/arch/m68k/include/asm/thread_info.h
+++ b/arch/m68k/include/asm/thread_info.h
@@ -64,6 +64,7 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_NOTIFY_RESUME	5	/* callback before returning to user */
 #define TIF_SIGPENDING		6	/* signal pending */
 #define TIF_NEED_RESCHED	7	/* rescheduling necessary */
+#define TIF_SECCOMP		13	/* seccomp syscall filtering active */
 #define TIF_DELAYED_TRACE	14	/* single step a syscall */
 #define TIF_SYSCALL_TRACE	15	/* syscall trace active */
 #define TIF_MEMDIE		16	/* is terminating due to OOM killer */
@@ -72,6 +73,7 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
+#define _TIF_SECCOMP		(1 << TIF_SECCOMP)
 #define _TIF_DELAYED_TRACE	(1 << TIF_DELAYED_TRACE)
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
diff --git a/arch/m68k/kernel/ptrace.c b/arch/m68k/kernel/ptrace.c
index 74d58a8..bc2490c 100644
--- a/arch/m68k/kernel/ptrace.c
+++ b/arch/m68k/kernel/ptrace.c
@@ -19,6 +19,7 @@
 #include <linux/ptrace.h>
 #include <linux/user.h>
 #include <linux/signal.h>
+#include <linux/seccomp.h>
 #include <linux/tracehook.h>
 
 #include <linux/uaccess.h>
@@ -277,6 +278,10 @@ asmlinkage int syscall_trace_enter(void)
 
 	if (test_thread_flag(TIF_SYSCALL_TRACE))
 		ret = tracehook_report_syscall_entry(task_pt_regs(current));
+
+	if (secure_computing() == -1)
+		return -1;
+
 	return ret;
 }
 
-- 
2.7.4