Kernel: Add pledge() syscall :^)

This patch implements basic support for OpenBSD-style pledge().
pledge() allows programs to incrementally reduce their set of allowed
syscalls, which are divided into categories that each make up a subset
of POSIX functionality.

If a process violates one of its pledged promises by attempting to call
a syscall that it previously said it wouldn't call, the process is
immediately terminated with an uncatchable SIGABRT.

This is by no means complete, and we'll need to add more checks in
various places to ensure that promises are being kept.

But it is pretty cool! :^)

Libraries/LibC/unistd.cpp

@@ -652,4 +652,16 @@ int chroot(const char* path)
  int rc = syscall(SC_chroot, path, strlen(path));
  __RETURN_WITH_ERRNO(rc, rc, -1);
 }
+
+int pledge(const char* promises, const char* execpromises)
+{
+ Syscall::SC_pledge_params params {
+ { promises, promises ? strlen(promises) : 0 },
+ { execpromises, execpromises ? strlen(execpromises) : 0 }
+ };
+ int rc = syscall(SC_pledge, &params);
+ __RETURN_WITH_ERRNO(rc, rc, -1);
 }
+
+}
+

Libraries/LibC/unistd.h

@@ -113,6 +113,7 @@ int halt();
 int reboot();
 int mount(const char* source, const char* target, const char* fs_type, int flags);
 int umount(const char* mountpoint);
+int pledge(const char* promises, const char* execpromises);
 
 enum {
  _PC_NAME_MAX,