MAC/veriexec implements a verified execution environment using the MAC

MAC/veriexec implements a verified execution environment using the MAC
framework.

The code is organized into a few distinct pieces:

* The meta-data store (in veriexec_metadata.c) which maps a file system
  identifier, file identifier, and generation key tuple to veriexec
  meta-data record.

* Fingerprint management (in veriexec_fingerprint.c) which deals with
  calculating the cryptographic hash for a file and verifying it. It also
  manages the loadable fingerprint modules.

* MAC policy implementation (in mac_veriexec.c) which implements the
  following MAC methods:

mpo_init
  Initializes the veriexec state, meta-data store, fingerprint modules,
  and registers mount and unmount EVENTHANDLERs

mpo_syscall
  Implements the following per-policy system calls:
  MAC_VERIEXEC_CHECK_FD_SYSCALL
    Check a file descriptor to see if the referenced file has a valid
    fingerprint.
  MAC_VERIEXEC_CHECK_PATH_SYSCALL
    Check a path to see if the referenced file has a valid fingerprint.

mpo_kld_check_load
  Check if loading a kld is allowed. This checks if the referenced vnode
  has a valid fingerprint.

mpo_mount_destroy_label
  Clears the veriexec slot data in a mount point label.

mpo_mount_init_label
  Initializes the veriexec slot data in a mount point label.
  The file system identifier is saved in the veriexec slot data.

mpo_priv_check
  Check if a process is allowed to write to /dev/kmem and /dev/mem
  devices.
  If a process is flagged as trusted, it is allowed to write.

mpo_proc_check_debug
  Check if a process is allowed to be debugged. If a process is not
  flagged with VERIEXEC_NOTRACE, then debugging is allowed.

mpo_vnode_check_exec
  Check is an exectuable is allowed to run. If veriexec is not enforcing
  or the executable has a valid fingerprint, then it is allowed to run.
  NOTE: veriexec will complain about mismatched fingerprints if it is
  active, regardless of the state of the enforcement.

mpo_vnode_check_open
  Check is a file is allowed to be opened. If verification was not
  requested, veriexec is not enforcing, or the file has a valid
  fingerprint, then veriexec will allow the file to be opened.

mpo_vnode_copy_label
  Copies the veriexec slot data from one label to another.

mpo_vnode_destroy_label
  Clears the veriexec slot data in a vnode label.

mpo_vnode_init_label
  Initializes the veriexec slot data in a vnode label.
  The fingerprint status for the file is stored in the veriexec slot data.

* Some sysctls, under security.mac.veriexec, for setting debug level,
  fetching the current state in a human-readable form, and dumping the
  fingerprint database are implemented.

* The MAC policy implementation source file also contains some utility
  functions.

* A set of fingerprint modules for the following cryptographic hash
  algorithms:
  RIPEMD-160, SHA1, SHA2-256, SHA2-384, SHA2-512

* Loadable module builds for MAC/veriexec and fingerprint modules.

 WARNING: Using veriexec with NFS (or other network-based) file systems is
          not recommended as one cannot guarantee the integrity of the files
          served, nor the uniqueness of file system identifiers which are
          used as key in the meta-data store.

Reviewed by:	ian, jtl
Obtained from:	Juniper Networks, Inc.
Differential Revision:	https://reviews.freebsd.org/D8554