[PATCH v6 2/2] m68k: add kernel seccomp support

Michael Schmitz
2021-06-24T00:46:11Z

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>

--
Changes from v5:

Geert Uytterhoeven:
- correct wrong offset for d1-d5 register copy
- update Documentation/features/seccomp/seccomp-filter/arch-support.txt
---
.../seccomp/seccomp-filter/arch-support.txt | 2 +-
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 ++++
6 files changed, 54 insertions(+), 1 deletion(-)
create mode 100644 arch/m68k/include/asm/seccomp.h

diff --git a/Documentation/features/seccomp/seccomp-filter/arch-support.txt b/Documentation/features/seccomp/seccomp-filter/arch-support.txt
index 26eec58..be71f20 100644
--- a/Documentation/features/seccomp/seccomp-filter/arch-support.txt
+++ b/Documentation/features/seccomp/seccomp-filter/arch-support.txt
@@ -14,7 +14,7 @@
| h8300: | TODO |
| hexagon: | TODO |
| ia64: | TODO |
- | m68k: | TODO |
+ | m68k: | ok |
| microblaze: | TODO |
| mips: | ok |
| nds32: | TODO |
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..ab8ab94e 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->d1, 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