EVMCTL(1)
=========

NAME
----

evmctl - IMA/EVM signing utility


SYNOPSIS
--------

evmctl [options] <command> [OPTIONS]


DESCRIPTION
-----------

The evmctl utility can be used for producing and verifying digital signatures,
which are used by Linux kernel integrity subsystem (IMA/EVM). It can be also
used to import keys into the kernel keyring.

COMMANDS
--------

 --version
 help <command>
 import  [--rsa (deprecated)] pubkey keyring
 sign [-r] [--imahash | --imasig ] [--key key] [--pass[=<password>] file
 verify file
 ima_sign [--sigfile] [--key key] [--pass[=<password>]] file
 ima_verify file
 ima_setxattr [--sigfile file]
 ima_hash file
 ima_measurement [--ignore-violations] [--verify-sig [--key "key1, key2, ..."]]
   [--pcrs [hash-algorithm,]file [--pcrs hash-algorithm,file] ...]
   [--verify-bank hash-algorithm] file
 ima_boot_aggregate [--pcrs hash-algorithm,file] [TPM 1.2 BIOS event log]
   [--hwtpm]
 ima_fix [-t fdsxm] path
 ima_clear [-t fdsxm] path
 sign_hash [--veritysig] [--key key] [--pass=<password>]
 hmac [--imahash | --imasig] [--hmackey key] file


OPTIONS
-------

  -a, --hashalgo     sha1, sha224, sha256, sha384, sha512, streebog256, streebog512 (default: sha256)
  -s, --imasig       make IMA signature
      --veritysig    sign an fs-verity file digest hash
  -d, --imahash      make IMA hash
  -f, --sigfile      store IMA signature in .sig file instead of xattr
      --xattr-user   store xattrs in user namespace (for testing purposes)
      --rsa          use RSA key type and signing scheme v1 (deprecated)
  -k, --key          path to signing key (default: /etc/keys/{privkey,pubkey}_evm.pem)
                     or a pkcs11 URI
      --keyid n      overwrite signature keyid with a 32-bit value in hex (for signing)
      --keyid-from-cert file
                     read keyid value from SKID of a x509 cert file
  -o, --portable     generate portable EVM signatures
  -p, --pass         password for encrypted signing key; use -p<password>
  -r, --recursive    recurse into directories (sign)
  -t, --type         file types to fix 'fxm' (f: file)
                     x - skip fixing if both ima and evm xattrs exist (use with caution)
                     m - stay on the same filesystem (like 'find -xdev')
  -n                 print result to stdout instead of setting xattr
  -u, --uuid         use custom FS UUID for EVM (unspecified: from FS, empty: do not use)
      --smack        use extra SMACK xattrs for EVM
      --m32          force EVM hmac/signature for 32 bit target system
      --m64          force EVM hmac/signature for 64 bit target system
      --ino          use custom inode for EVM
      --uid          use custom UID for EVM
      --gid          use custom GID for EVM
      --mode         use custom Mode for EVM
      --generation   use custom Generation for EVM(unspecified: from FS, empty: use 0)
      --ima          use custom IMA signature for EVM
      --selinux      use custom Selinux label for EVM
      --caps         use custom Capabilities for EVM(unspecified: from FS, empty: do not use)
      --pcrs         file containing TPM pcrs, one per hash-algorithm/bank
      --verify-sig   verify the file signature based on the file hash, both
                     stored in the template data.
      --engine e     preload OpenSSL engine e (such as: gost) is deprecated
      --provider p   preload OpenSSL provider (such as: pkcs11)
      --ignore-violations ignore ToMToU measurement violations
      --hmackey      path to symmetric key (default: /etc/keys/evm-key-plain)
      --v2           create V2 signatures; this is the default
      --v3           create V3 signatures; this requires Linux 7.2 or later
  -v                 increase verbosity level
  -h, --help         display this help and exit

Environment variables:

EVMCTL_KEY_PASSWORD  : Private key password to use; do not use --pass option


INTRODUCTION
------------

Linux kernel integrity subsystem is comprised of a number of different components
including the Integrity Measurement Architecture (IMA), Extended Verification Module
(EVM), IMA-appraisal extension, digital signature verification extension and audit
measurement log support.

The evmctl utility is used for producing and verifying digital signatures, which
are used by the Linux kernel integrity subsystem. It is also used for importing keys
into the kernel keyring.

Linux integrity subsystem allows to use IMA and EVM signatures. EVM signature
protects file metadata, such as file attributes and extended attributes. IMA
signature protects file content.

For more detailed information about integrity subsystem it is recommended to follow
resources in RESOURCES section.


EVM HMAC and signature metadata
-------------------------------

EVM protects file metadata by including following attributes into HMAC and signature
calculation: inode number, inode generation, UID, GID, file mode, security.selinux,
security.SMACK64, security.ima, security.capability.

EVM HMAC and signature in may also include additional file and file system attributes.
Currently supported additional attributes are filesystem UUID and extra SMACK
extended attributes.

Kernel configuration option CONFIG_EVM_ATTR_FSUUID controls whether to include
filesystem UUID into HMAC and enabled by default. Therefore evmctl also includes
fsuuid by default. Providing '--uuid' option without parameter allows to disable
usage of fs uuid. Providing '--uuid=UUID' option with parameter allows to use
custom UUID. Providing the '--portable' option will disable usage of the fs uuid
and also the inode number and generation.

Kernel configuration option CONFIG_EVM_EXTRA_SMACK_XATTRS controls whether to
include additional SMACK extended attributes into HMAC. They are following:
security.SMACK64EXEC, security.SMACK64TRANSMUTE and security.SMACK64MMAP.
evmctl '--smack' options enables that.


Key and signature formats
-------------------------

Linux integrity subsystem supports three types of signature and respectively two
key formats.

First key format (v1) is pure RSA key encoded in PEM a format and uses own signature
format. It is now non-default format and requires to provide evmctl '--rsa' option
for signing and importing the key.

Second key format uses X509 DER encoded public key certificates and uses asymmetric key support
in the kernel (since kernel 3.9). CONFIG_INTEGRITY_ASYMMETRIC_KEYS must be enabled (default).

For v2 and v3 signatures x509 certificate (containing the public key) could be appended to the
private key (they both are in PEM format) to automatically extract keyid from its Subject
Key Identifier (SKID). v3 signatures can be created with the --v3 option. This signature format
is required for signing with ML-DSA keys.

Integrity keyrings
----------------

Integrity subsystem uses dedicated IMA/EVM keyrings to search for signature verification
keys - '_ima' and '_evm' respectively.

Since 3.13 IMA allows to declare IMA keyring as trusted. It allows only to load keys,
signed by a key from the system keyring (.system). It means self-signed keys are not
allowed. This is a default behavior unless CONFIG_IMA_TRUSTED_KEYRING is undefined.
IMA trusted keyring is has different name '.ima'. Trusted keyring requires X509
public key certificates. Old version RSA public keys are not compatible with trusted
keyring.


Generate EVM encrypted keys
---------------------------

EVM encrypted key is used for EVM HMAC calculation:

    # create and save the key kernel master key (user type)
    # LMK is used to encrypt encrypted keys
    keyctl add user kmk "`dd if=/dev/urandom bs=1 count=32 2>/dev/null`" @u
    keyctl pipe `keyctl search @u user kmk` > /etc/keys/kmk

    # create the EVM encrypted key
    keyctl add encrypted evm-key "new user:kmk 64" @u
    keyctl pipe `keyctl search @u encrypted evm-key` >/etc/keys/evm-key


Generate EVM trusted keys (TPM based)
-------------------------------------

Trusted EVM keys are keys which a generate with the help of TPM.
They are not related to integrity trusted keys.

    # create and save the key kernel master key (user type)
    keyctl add trusted kmk "new 32" @u
    keyctl pipe `keyctl search @u trusted kmk` >kmk

    # create the EVM trusted key
    keyctl add encrypted evm-key "new trusted:kmk 32" @u
    keyctl pipe `keyctl search @u encrypted evm-key` >evm-key


Generate signing and verification keys
--------------------------------------

Generate private key in plain text format:

    openssl genrsa -out privkey_evm.pem 2048

Generate encrypted private key:

    openssl genrsa -des3 -out privkey_evm.pem 2048

Make encrypted private key from unencrypted:

    openssl rsa -in /etc/keys/privkey_evm.pem -out privkey_evm_enc.pem -des3

Generate self-signed X509 public key certificate and private key for using kernel
asymmetric keys support:

    openssl req -new -nodes -utf8 -sha256 -days 36500 -batch \
    	        -x509 -config x509_evm.genkey \
	        -outform DER -out x509_evm.der -keyout privkey_evm.pem

Create an elliptic curve (EC) key (supported since Linux v5.13)

    openssl ecparam -name prime256v1 -genkey -out privkey_evm.pem

Generate self-signed x509 EC public key certificate and private key for using
kernel asymmetric key support (supported since Linux v5.13):

   openssl req -new -nodes -utf8 -sha1 -days 36500 -batch \
                -x509 -config x509_evm.genkey \
                -outform DER -out x509_evm.der -keyout privkey_evm.pem \
                -newkey ec -pkeyopt ec_paramgen_curve:prime256v1

Configuration file x509_evm.genkey:

	# Beginning of the file
	[ req ]
	default_bits = 2048
	distinguished_name = req_distinguished_name
	prompt = no
	string_mask = utf8only
	x509_extensions = myexts

	[ req_distinguished_name ]
	O = Magrathea
	CN = Glacier signing key
	emailAddress = slartibartfast@magrathea.h2g2

	[ myexts ]
	basicConstraints=critical,CA:FALSE
	keyUsage=digitalSignature
	extendedKeyUsage=critical,codeSigning
	subjectKeyIdentifier=hash
	authorityKeyIdentifier=keyid
	# EOF


Generate public key for using RSA key format:

    openssl rsa -pubout -in privkey_evm.pem -out pubkey_evm.pem

Similarly generate public EC key:

    openssl ec -pubout -in privkey_evm.pem -out pubkey_evm.pem

Copy keys to /etc/keys:

    cp pubkey_evm.pem /etc/keys
    scp pubkey_evm.pem target:/etc/keys
 or
    cp x509_evm.pem /etc/keys
    scp x509_evm.pem target:/etc/keys


Generate trusted keys
---------------------

Generation of trusted keys is a bit more complicated process and involves
following steps:

* Creation of local IMA certification authority (CA).
  It consist of private and public key certificate which are used
  to sign and verify other keys.
* Build Linux kernel with embedded local IMA CA X509 certificate.
  It is used to verify other keys added to the '.ima' trusted keyring
* Generate IMA private signing key and verification public key certificate,
  which is signed using local IMA CA private key.

Configuration file ima-local-ca.genkey:

	# Beginning of the file
	[ req ]
	default_bits = 2048
	distinguished_name = req_distinguished_name
	prompt = no
	string_mask = utf8only
	x509_extensions = v3_ca

	[ req_distinguished_name ]
	O = IMA-CA
	CN = IMA/EVM certificate signing key
	emailAddress = ca@ima-ca

	[ v3_ca ]
	basicConstraints=CA:TRUE
	subjectKeyIdentifier=hash
	authorityKeyIdentifier=keyid:always,issuer
	keyUsage = cRLSign, keyCertSign
	# EOF

Note: To generated elliptic curve keys add the following parameters to
      the 'req' commands below (supported since Linux v5.13):

      -newkey ec -pkeyopt ec_paramgen_curve:prime256v1


Generate private key and X509 public key certificate:

 openssl req -new -x509 -utf8 -sha256 -days 3650 -batch -config $GENKEY \
             -outform DER -out ima-local-ca.x509 -keyout ima-local-ca.priv

Produce X509 in DER format for using while building the kernel:

 openssl x509 -inform DER -in ima-local-ca.x509 -out ima-local-ca.pem

Configuration file ima.genkey:

	# Beginning of the file
	[ req ]
	default_bits = 2048
	distinguished_name = req_distinguished_name
	prompt = no
	string_mask = utf8only
	x509_extensions = v3_usr

	[ req_distinguished_name ]
	O = `hostname`
	CN = `whoami` signing key
	emailAddress = `whoami`@`hostname`

	[ v3_usr ]
	basicConstraints=critical,CA:FALSE
	#basicConstraints=CA:FALSE
	keyUsage=digitalSignature
	#keyUsage = nonRepudiation, digitalSignature, keyEncipherment
	subjectKeyIdentifier=hash
	authorityKeyIdentifier=keyid
	#authorityKeyIdentifier=keyid,issuer
	# EOF


Generate private key and X509 public key certificate signing request:

 openssl req -new -nodes -utf8 -sha256 -days 365 -batch -config $GENKEY \
             -out csr_ima.pem -keyout privkey_ima.pem

Sign X509 public key certificate signing request with local IMA CA private key:

 openssl x509 -req -in csr_ima.pem -days 365 -extfile $GENKEY -extensions v3_usr \
              -CA ima-local-ca.pem -CAkey ima-local-ca.priv -CAcreateserial \
              -outform DER -out x509_ima.der


Sign file data and metadata
---------------------------

Default key locations:

 Private RSA key: /etc/keys/privkey_evm.pem
 Public RSA key: /etc/keys/pubkey_evm.pem
 X509 certificate: /etc/keys/x509_evm.der

Options to remember: '-k', '-r', '--rsa', '--uuid', '--smack'.

Sign file with EVM signature and calculate hash value for IMA:

    evmctl sign --imahash test.txt

Sign file with both IMA and EVM signatures:

    evmctl sign --imasig test.txt:

Sign file with IMA signature:

    evmctl ima_sign test.txt

Sign recursively whole filesystem:

    evmctl -r sign --imahash /

Fix recursively whole filesystem:

    evmctl -r ima_fix /

Sign filesystem selectively using 'find' command:

    find / \( -fstype rootfs -o -fstype ext4 \) -exec evmctl sign --imahash '{}' \;

Fix filesystem selectively using 'find' command:

    find / \( -fstype rootfs -o -fstype ext4 \) -exec sh -c "< '{}'" \;


Initialize IMA/EVM at early boot
--------------------------------

IMA/EVM initialization should be normally done from initial RAM file system
before mounting root filesystem.

Here is Ubuntu initramfs example script (/etc/initramfs-tools/scripts/local-top/ima.sh)

    # mount securityfs if not mounted
    SECFS=/sys/kernel/security
    grep -q  $SECFS /proc/mounts || mount -n -t securityfs securityfs $SECFS

    # search for IMA trusted keyring, then for untrusted
    ima_id="`awk '/\.ima/ { printf "%d", "0x"$1; }' /proc/keys`"
    if [ -z "$ima_id" ]; then
        ima_id=`keyctl search @u keyring _ima 2>/dev/null`
        if [ -z "$ima_id" ]; then
	    ima_id=`keyctl newring _ima @u`
        fi
    fi
    # import IMA X509 certificate
    evmctl import /etc/keys/x509_ima.der $ima_id

    # search for EVM keyring
    evm_id=`keyctl search @u keyring _evm 2>/dev/null`
    if [ -z "$evm_id" ]; then
        evm_id=`keyctl newring _evm @u`
    fi
    # import EVM X509 certificate
    evmctl import /etc/keys/x509_evm.der $evm_id

    # a) import EVM encrypted key
    cat /etc/keys/kmk | keyctl padd user kmk @u
    keyctl add encrypted evm-key "load `cat /etc/keys/evm-key`" @u
    # OR
    # b) import EVM trusted key
    keyctl add trusted kmk "load `cat /etc/keys/kmk`" @u
    keyctl add encrypted evm-key "load `cat /etc/keys/evm-key`" @u

    # enable EVM
    echo "1" > /sys/kernel/security/evm

Optionally it is possible also to forbid adding, removing of new public keys
and certificates into keyrings and revoking keys using 'keyctl setperm' command:

    # protect EVM keyring
    keyctl setperm $evm_id 0x0b0b0000
    # protect IMA keyring
    keyctl setperm $ima_id 0x0b0b0000
    # protecting IMA key from revoking (against DoS)
    ima_key=`evmctl import /etc/keys/x509_ima.der $ima_id`
    keyctl setperm $ima_key 0x0b0b0000


When using plain RSA public keys in PEM format, use 'evmctl import --rsa' for importing keys:

    evmctl import --rsa /etc/keys/pubkey_evm.pem $evm_id

Latest version of keyctl allows to import X509 public key certificates:

    cat /etc/keys/x509_ima.der | keyctl padd asymmetric '' $ima_id


VERIFYING THE IMA MEASUREMENT LIST
-----------------------------------

The IMA measurement list is recorded by the kernel in binary format at:

    <securityfs>/ima/binary_runtime_measurements

where <securityfs> is the mount point of securityfs, conventionally
/sys/kernel/security, determinable from /proc/mounts.

This file is only accessible on a running Linux system with IMA enabled and
securityfs mounted.  It is not available in all environments — for example,
remote attestation servers receive the binary measurement log together with
a TPM quote and must verify the log without direct access to the
original files.

`evmctl ima_measurement` operates on the binary measurement log file passed
to it, whether that is the live kernel file or a copy received as part of a
broader attestation workflow.

`evmctl ima_measurement` walks the measurement list once, simultaneously
extending the template digests into a running PCR calculation and, when
`--verify-sig` is specified, verifying the IMA signature in each record
against the file hash stored in that same record.  It is this PCR match
that establishes the integrity of the log as a whole — confirming the log
has not been tampered with — and gives the per-record `--verify-sig`
signature verification its meaning.

PCR values
~~~~~~~~~~

`evmctl ima_measurement` obtains TPM PCR values from the first available
source in the following order:

 - Per-bank files specified via --pcrs
 - TPM 1.2 sysfs (/sys/class/tpm/tpm0/device/pcrs or
   /sys/class/misc/tpm0/device/pcrs)
 - TPM 2.0 sysfs (/sys/class/tpm/tpm0/pcr-<algo>/<n>), enabled via --hwtpm
 - A TSS userspace application via tpm2_pcr_read()

The PCR values are read before walking the binary measurement list.  After
each extend, the re-calculated PCR values are compared against the TPM PCR
values.  Once all banks match the walk stops, since any remaining entries
were added after the PCR values were read.

If no PCR values can be obtained from any source, PCR verification is
skipped, but `--verify-sig` can still be used independently to verify the
signatures within the log records. However, without PCR verification
there is no integrity guarantee that the measurement list itself has
not been tampered with.

Verifying IMA signatures with --verify-sig
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

For each `ima-sig` or `ima-sigv2` template record in the measurement list,
`--verify-sig` verifies that the IMA signature stored in the template data
was produced over the file hash also stored in that same template record,
using a trusted key supplied via `--key`.  Both the signature and the hash
being verified come from within the log record itself — no access to the
original file on disk is required.

`--verify-sig` requires verification keys to be explicitly supplied via
`--key`.  If not provided, `evmctl ima_measurement` falls back to
/etc/keys/x509_evm.der; if that file is absent or unreadable, signature
verification will fail for all signed entries.

Usage:

    evmctl ima_measurement --verify-sig --key "key1.der,key2.der,..." \
        <securityfs>/ima/binary_runtime_measurements

Entries that carry no IMA signature (files measured using templates such as
`ima-ng`) are silently skipped by `--verify-sig`.

Fedora example — release signing keys from fedora-gpg-keys
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

On Fedora, the fedora-gpg-keys package installs release-specific IMA signing
certificates under /etc/keys/ima/, for example:

    /etc/keys/ima/fedora-45-ima.der

These certificates are loaded onto the kernel's .ima keyring at early boot by
dracut, provided the following dracut modules are enabled:

 - 96securityfs  — mounts securityfs at /sys/kernel/security
 - 97masterkey   — sets up the kernel master key infrastructure
 - 98integrity   — loads IMA/EVM keys from /etc/keys/ima/ onto the .ima keyring

To verify a Fedora binary measurement log against the current release IMA
signing certificate:

    evmctl ima_measurement --verify-sig --key /etc/keys/ima/fedora-45-ima.der \
        <securityfs>/ima/binary_runtime_measurements

Multiple keys can be supplied as a comma-separated list if files were
signed across more than one release:

    evmctl ima_measurement --verify-sig \
        --key "/etc/keys/ima/fedora-43-ima.der,/etc/keys/ima/fedora-44-ima.der,/etc/keys/ima/fedora-45-ima.der" \
        /path/to/saved/binary_runtime_measurements

ToMToU and open_writers violations and --ignore-violations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The measurement list may contain two types of integrity violation entries.
A `ToMToU` (Time-of-Measure/Time-of-Use) violation is recorded when a file
that has already been measured is subsequently opened for write.  An
`open_writers` violation is recorded when a file that must be measured is
opened for read while already open for write.

In both cases the entire template digest is zeroed out in the violation
entry.  When extended into the TPM, the zeroed digest is extended as 0xff
bytes rather than 0x00.  By default, `evmctl ima_measurement` treats these
as errors and the PCR comparison will fail.

The `--ignore-violations` flag allows the PCR comparison to succeed in the
presence of violation entries by substituting 0xff for the PCR extension:

    evmctl ima_measurement --verify-sig --ignore-violations \
        --key /etc/keys/ima/fedora-45-ima.der \
        <securityfs>/ima/binary_runtime_measurements

Use `--ignore-violations` in development or test environments where
concurrent file access is expected and violations are benign.  Do not use
it in production security-critical contexts where a violation entry may
indicate a genuine race condition or tampering attempt — in those cases the
violation should be investigated rather than silently skipped.


FILES
-----

Examples of scripts to generate X509 public key certificates:

 /usr/share/doc/ima-evm-utils/ima-genkey-self.sh
 /usr/share/doc/ima-evm-utils/ima-genkey.sh
 /usr/share/doc/ima-evm-utils/ima-gen-local-ca.sh

All three scripts accept an optional keyalgo argument selecting the key
algorithm and parameters.  The following algorithms are supported:

  rsa:2048, rsa:3072, rsa:4096
  prime256v1, secp384r1, secp521r1
  mldsa44, mldsa65, mldsa87

The default is rsa:2048 when no keyalgo argument is provided.

ima-genkey-self.sh [keyalgo]
    Generate an EVM/IMA file signing key and a self-signed CA certificate
    using the same key.

ima-gen-local-ca.sh [keyalgo]
    Generate a local IMA certificate authority key and self-signed
    certificate.  Used in conjunction with ima-genkey.sh to establish a
    local trust chain.

ima-genkey.sh [keyalgo] [filename suffix]
    Generate an EVM/IMA file signing key signed by the local CA created
    with ima-gen-local-ca.sh.  An optional filename suffix prevents the
    generated certificate from being overwritten by subsequent invocations.

The mldsa44, mldsa65, and mldsa87 algorithms are post-quantum ML-DSA
signing algorithms (FIPS 204), supported from Linux 7.2 onwards.  ML-DSA
support in IMA and EVM is limited to sigv3 signatures.

Fedora release IMA signing certificates (fedora-gpg-keys package):

 /etc/keys/ima/fedora-43-ima.der
 /etc/keys/ima/fedora-44-ima.der
 /etc/keys/ima/fedora-45-ima.der


AUTHOR
------

Written by Dmitry Kasatkin and contributors.  For a full list of contributors
see the git commit history at:

 https://github.com/linux-integrity/ima-evm-utils/commits/master


RESOURCES
---------

 https://github.com/linux-integrity/ima-evm-utils
 https://ima-doc.readthedocs.io/en/latest/


COPYING
-------

Copyright (C) 2012 - 2026 Linux Integrity Project.

ima-evm-utils is dual-licensed:

 - libimaevm is provided under the terms of the GNU Lesser General Public
   License (LGPL-2.0-or-later).  See COPYING.LGPL.

 - evmctl is provided under the terms of the GNU General Public License
   (GPL-2.0-or-later).  See COPYING.

See LICENSES.txt for the full license breakdown.