VERIEXEC(9)            NetBSD Kernel Developer's Manual            VERIEXEC(9)

NAME
     veriexec -- in-kernel file integrity subsystem KPI

SYNOPSIS
     #include <sys/verified_exec.h>

     void
     veriexec_init(void);

     bool
     veriexec_lookup(struct vnode *vp);

     int
     veriexec_verify(struct lwp *l, struct vnode *vp, const u_char *name,
         int flag, bool *found);

     void
     veriexec_purge(struct vnode *vp);

     int
     veriexec_fpops_add(const char *fp_type, size_t hash_len, size_t ctx_size,
         veriexec_fpop_init_t init, veriexec_fpop_update_t update,
         veriexec_fpop_final_t final);

     int
     veriexec_file_add(struct lwp *l, prop_dictionary_t dict);

     int
     veriexec_file_delete(struct lwp *l, struct vnode *vp);

     int
     veriexec_table_delete(struct lwp *l, struct mount *mp);

     int
     veriexec_flush(struct lwp *l);

     int
     veriexec_openchk(struct lwp *l, struct vnode *vp, const char *path,
         int fmode);

     int
     veriexec_renamechk(struct lwp *l, struct vnode *fromvp,
         const char *fromname, struct vnode *tovp, const char *toname);

     int
     veriexec_removechk(struct lwp *l, struct vnode *vp, const char *name);

     int
     veriexec_unmountchk(struct mount *mp);

     int
     veriexec_convert(struct vnode *vp, prop_dictionary_t rdict);

     int
     veriexec_dump(struct lwp *l, prop_array_t rarray);

DESCRIPTION
     veriexec is the KPI for Veriexec, the NetBSD in-kernel file integrity
     subsystem.  It is responsible for managing the supported hashing algo-
     rithms, fingerprint calculation and comparison, file monitoring tables,
     and relevant hooks to enforce the Veriexec policy.

FUNCTIONS
   Core Routines
     veriexec_init(void)
              Initialize the Veriexec subsystem.  Called only once during sys-
              tem startup.

     veriexec_lookup(vp)
              Check if vp is monitored by Veriexec.  Returns true if it is, or
              false otherwise.

     veriexec_verify(l, vp, name, flag, found)
              Verifies the digital fingerprint of vp.  name is the filename,
              and flag is the access flag.  The access flag can be one of:

              VERIEXEC_DIRECT    The file was executed directly via execve(2).

              VERIEXEC_INDIRECT  The file was executed indirectly, either as
                                 an interpreter for a script or mapped to an
                                 executable memory region.

              VERIEXEC_FILE      The file was opened for reading/writing.

              l is the LWP for the request context.

              An optional argument, found, is a pointer to a boolean indicat-
              ing whether an entry for the file was found in the Veriexec
              tables.

     veriexec_purge(vp)
              Purge the file entry for vp.  This invalidates the fingerprint
              so it will be evaluated next time the file is accessed.

   Fingerprint Related Routines
     veriexec_fpops_add(fp_type, hash_len, ctx_size, init, update, final)
              Add support for fingerprinting algorithm fp_type with binary
              hash length hash_len and calculation context size ctx_size to
              Veriexec.  init, update, and final are the routines used to ini-
              tialize, update, and finalize a calculation context.

   Table Management Routines
     veriexec_file_add(l, dict)
              Add a Veriexec entry for the file described by dict.

              dict is expected to have the following:

              Name          Type      Purpose
              file          string    filename
              entry-type    uint8     entry type flags (see veriexec(4))
              fp-type       string    fingerprint hashing algorithm
              fp            data      the fingerprint

     veriexec_file_delete(l, vp)
              Remove Veriexec entry for vp.

     veriexec_table_delete(l, mp)
              Remove Veriexec table for mount-point mp.

     veriexec_flush(l)
              Delete all Veriexec tables.

   Hook Handlers
     veriexec_openchk(l, vp, path, fmode)
              Called when a file is opened.

              l is the LWP opening the file, vp is a vnode for the file being
              opened as returned from namei(9).  If NULL, the file is being
              created.  path is the pathname for the file (not necessarily a
              full path), and fmode are the mode bits with which the file was
              opened.

     veriexec_renamechk(l, fromvp, fromname, tovp, toname)
              Called when a file is renamed.

              fromvp and fromname are the vnode and filename of the file being
              renamed.  tovp and toname are the vnode and filename of the tar-
              get file.  l is the LWP renaming the file.

              Depending on the strict level, veriexec will either track
              changes appropriately or prevent the rename.

     veriexec_removechk(l, vp, name)
              Called when a file is removed.

              vp is the vnode of the file being removed, and name is the file-
              name.  l is the LWP removing the file,

              Depending on the strict level, veriexec will either clean-up
              after the file or prevent its removal.

     veriexec_unmountchk(mp)
              Checks if the current strict level allows mp to be unmounted.

   Miscellaneous Routines
     veriexec_convert(vp, rdict)
              Convert Veriexec entry for vp to human-readable proplib(3) dic-
              tionary, rdict, with the following elements:

              Name          Type      Purpose
              entry-type    uint8     entry type flags (see veriexec(4))
              status        uint8     entry status (see below)
              fp-type       string    fingerprint hashing algorithm
              fp            data      the fingerprint

              The ``status'' can be one of the following:

              Status                  Meaning
              FINGERPRINT_NOTEVAL     not evaluated
              FINGERPRINT_VALID       fingerprint match
              FINGERPRINT_MISMATCH    fingerprint mismatch

              If no entry was found, ENOENT is returned.  Otherwise, zero.

     veriexec_dump(l, rarray)
              Fill rarray with entries for all files monitored by Veriexec
              that have a filename associated with them.

              Each element in rarray is a dictionary with the same elements as
              filled by veriexec_convert(), with an additional field,
              ``file'', containing the filename.

FILES
     Path                                Purpose
     src/sys/dev/verified_exec.c         driver for userland communication
     src/sys/sys/verified_exec.h         shared (userland/kernel) header file
     src/sys/kern/kern_verifiedexec.c    subsystem code
     src/sys/kern/vfs_syscalls.c         rename, remove, and unmount policies
     src/sys/kern/vfs_vnops.c            regular file access policy

SEE ALSO
     proplib(3), sysctl(3), veriexec(4), security(7), sysctl(8),
     veriexecctl(8), veriexecgen(8), fileassoc(9)

AUTHORS
     Brett Lymn <blymn@NetBSD.org>
     Elad Efrat <elad@NetBSD.org>

CAVEATS
     There are two known issues with Veriexec that should be considered when
     using it.

   Remote File-systems
     There is an issue providing protection for files residing on mounts from
     remote hosts.  Because access to the file-system does not necessarily go
     through veriexec, there is no way to track on-disk changes.  While it is
     possible to minimize the effect by evaluating the file's fingerprint on
     each access without caching the result, a problem arises when a file is
     overwritten after its fingerprint has been evaluated and it is running on
     the local host.

     An attacker could potentially overwrite the file contents in the remote
     host at that point, and force a flush on the local host, resulting in
     paging in of the files from the disk, introducing malicious code into a
     supposedly safe address space.

     There is a fix for this issue, however due to dependencies on other work
     that is still in progress it has not been committed yet.

   Layered File-systems
     Due to VFS limitations, veriexec cannot track the same on-disk file
     across multiple layers of overlay file-systems.  Therefore, you cannot
     expect changes to files on overlay mounts will be detected simply because
     the underlying mount is monitored by veriexec.

     A workaround for this issue is listing all files, under all mounts, you
     want monitored in the signature file.

NetBSD 6.0                      March 18, 2011                      NetBSD 6.0

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