arm64: add seccomp support

secure_computing() is called first in syscall_trace_enter() so that
a system call will be aborted quickly without doing succeeding syscall
tracing if seccomp rules want to deny that system call.

On compat task, syscall numbers for system calls allowed in seccomp mode 1
are different from those on normal tasks, and so _NR_seccomp_xxx_32's need
to be redefined.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

4 files changed, 47 insertions, 0 deletions

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index f5412d628ff6..7c79c6494379 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -38,6 +38,7 @@ config ARM64
         select HAVE_ARCH_AUDITSYSCALL
         select HAVE_ARCH_JUMP_LABEL
         select HAVE_ARCH_KGDB
+        select HAVE_ARCH_SECCOMP_FILTER
         select HAVE_ARCH_TRACEHOOK
         select HAVE_BPF_JIT
         select HAVE_C_RECORDMCOUNT
@@ -455,6 +456,19 @@ config ARCH_HAS_CACHE_LINE_SIZE
 
 source "mm/Kconfig"
 
+config SECCOMP
+        bool "Enable seccomp to safely compute untrusted bytecode"
+        ---help---
+          This kernel feature is useful for number crunching applications
+          that may need to compute untrusted bytecode during their
+          execution. By using pipes or other transports made available to
+          the process as file descriptors supporting the read/write
+          syscalls, it's possible to isolate those applications in
+          their own address space using seccomp. Once seccomp is
+          enabled via prctl(PR_SET_SECCOMP), it cannot be disabled
+          and the task is only allowed to execute a few safe syscalls
+          defined by each seccomp mode.
+
 config XEN_DOM0
         def_bool y
         depends on XEN
diff --git a/arch/arm64/include/asm/seccomp.h b/arch/arm64/include/asm/seccomp.h
new file mode 100644
index 000000000000..c76fac979629
--- /dev/null
+++ b/arch/arm64/include/asm/seccomp.h
@@ -0,0 +1,25 @@
+/*
+ * arch/arm64/include/asm/seccomp.h
+ *
+ * Copyright (C) 2014 Linaro Limited
+ * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#ifndef _ASM_SECCOMP_H
+#define _ASM_SECCOMP_H
+
+#include <asm/unistd.h>
+
+#ifdef CONFIG_COMPAT
+#define __NR_seccomp_read_32            __NR_compat_read
+#define __NR_seccomp_write_32           __NR_compat_write
+#define __NR_seccomp_exit_32            __NR_compat_exit
+#define __NR_seccomp_sigreturn_32       __NR_compat_rt_sigreturn
+#endif /* CONFIG_COMPAT */
+
+#include <asm-generic/seccomp.h>
+
+#endif /* _ASM_SECCOMP_H */
diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
index 6d2bf419431d..49c9aefd24a5 100644
--- a/arch/arm64/include/asm/unistd.h
+++ b/arch/arm64/include/asm/unistd.h
@@ -31,6 +31,9 @@
  * Compat syscall numbers used by the AArch64 kernel.
  */
 #define __NR_compat_restart_syscall     0
+#define __NR_compat_exit                1
+#define __NR_compat_read                3
+#define __NR_compat_write               4
 #define __NR_compat_sigreturn           119
 #define __NR_compat_rt_sigreturn        173
 
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index f576781d8d3b..d882b833dbdb 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -27,6 +27,7 @@
 #include <linux/smp.h>
 #include <linux/ptrace.h>
 #include <linux/user.h>
+#include <linux/seccomp.h>
 #include <linux/security.h>
 #include <linux/init.h>
 #include <linux/signal.h>
@@ -1149,6 +1150,10 @@ static void tracehook_report_syscall(struct pt_regs *regs,
 
 asmlinkage int syscall_trace_enter(struct pt_regs *regs)
 {
+        /* Do the secure computing check first; failures should be fast. */
+        if (secure_computing() == -1)
+                return -1;
+
         if (test_thread_flag(TIF_SYSCALL_TRACE))
                 tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);