VERIEXEC(9)

💖 VERIEXEC(9) 💖

okay bestie, this is VERIEXEC(9) from the Kernel Developer's Manual, and it's giving full kernel file integrity subsystem KPI energy. Keep ur eyes on the details, because this page is all about the Veriexec KPI and its API. 💅

✨ NAME ✨

veriexec — in-kernel file integrity subsystem KPI.

🌸 SYNOPSIS 🌸

okay so first u include this header:

#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's the one managing the supported hashing algorithms, fingerprint calculation and comparison, file monitoring tables, and the relevant hooks that enforce the Veriexec policy. no cap, it's a whole little system. ✨

🎀 FUNCTIONS 🎀

💅 Core Routines 💅

• veriexec_init(void) — Initializes the Veriexec subsystem. It's called only once during system startup.
• veriexec_lookup(vp) — Checks 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 indicating whether an entry for the file was found in the Veriexec tables.

• veriexec_purge(vp) — Purges 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) — Adds 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 initialize, update, and finalize a calculation context.

🍓 Table Management Routines 🍓

• veriexec_file_add(l, dict) — Adds a Veriexec entry for the file described by dict.

dict is expected to have the following:

• 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) — Removes the Veriexec entry for vp.
• veriexec_table_delete(l, mp) — Removes the Veriexec table for mount-point mp.
• veriexec_flush(l) — Deletes 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 target 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 filename. 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) — Converts the Veriexec entry for vp to a human-readable proplib(3) dictionary, rdict, with the following elements:
  • 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:

• 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) — Fills 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 🌟

• src/sys/dev/veriexec.c — driver for userland communication.
• src/sys/sys/verified_exec.h — shared (userland/kernel) header file.
• src/sys/kern/kern_veriexec.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. Bestie, pls read these fr. 💀

🌐 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.

---

okay that's the whole page, bestie 💖 source/version: Debian; date: December 9, 2015; page: VERIEXEC(9) — bye, love u, slay 💅✨