move seccomp from /proc to a prctl

This reduces the memory footprint and it enforces that only the current
task can enable seccomp on itself (this is a requirement for a
strightforward [modulo preempt ;) ] TIF_NOTSC implementation).

Signed-off-by: Andrea Arcangeli <andrea@cpushare.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 34 insertions, 0 deletions

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index c3391b6020e8..1dfa8a509726 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -10,6 +10,7 @@
 #include <linux/sched.h>
 
 /* #define SECCOMP_DEBUG 1 */
+#define NR_SECCOMP_MODES 1
 
 /*
  * Secure computing mode 1 allows only read/write/exit/sigreturn.
@@ -54,3 +55,28 @@ void __secure_computing(int this_syscall)
 #endif
         do_exit(SIGKILL);
 }
+
+long prctl_get_seccomp(void)
+{
+        return current->seccomp.mode;
+}
+
+long prctl_set_seccomp(unsigned long seccomp_mode)
+{
+        long ret;
+
+        /* can set it only once to be even more secure */
+        ret = -EPERM;
+        if (unlikely(current->seccomp.mode))
+                goto out;
+
+        ret = -EINVAL;
+        if (seccomp_mode && seccomp_mode <= NR_SECCOMP_MODES) {
+                current->seccomp.mode = seccomp_mode;
+                set_thread_flag(TIF_SECCOMP);
+                ret = 0;
+        }
+
+ out:
+        return ret;
+}
diff --git a/kernel/sys.c b/kernel/sys.c
index ed92e2f03342..4d141ae3e802 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -31,6 +31,7 @@
 #include <linux/cn_proc.h>
 #include <linux/getcpu.h>
 #include <linux/task_io_accounting_ops.h>
+#include <linux/seccomp.h>
 
 #include <linux/compat.h>
 #include <linux/syscalls.h>
@@ -2242,6 +2243,13 @@ asmlinkage long sys_prctl(int option, unsigned long arg2, unsigned long arg3,
                         error = SET_ENDIAN(current, arg2);
                         break;
 
+                case PR_GET_SECCOMP:
+                        error = prctl_get_seccomp();
+                        break;
+                case PR_SET_SECCOMP:
+                        error = prctl_set_seccomp(arg2);
+                        break;
+
                 default:
                         error = -EINVAL;
                         break;