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EVMCTL(1)                                                            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] pubkey keyring
           sign [-r] [--imahash | --imasig ] [--portable] [--key key] [--pass password] file
           verify file
           ima_boot_aggregate [--pcrs hash-algorithm,file] [TPM 1.2 BIOS event log]
           ima_sign [--sigfile] [--key key] [--pass password] file
           ima_verify file
           ima_hash file
           ima_measurement [--ignore-violations] [--verify-sig [--key "key1, key2, ..."]]  [--pcrs [hash-algorithm,]file [--pcrs hash-algorithm,file] ...] file
           ima_fix [-t fdsxm] path
           sign_hash [--key key] [--pass password]
           hmac [--imahash | --imasig ] file
OPTIONS
           -a, --hashalgo     sha1 (default), sha224, sha256, sha384, sha512
           -s, --imasig       make IMA signature
           -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
           -k, --key          path to signing key (default: /etc/keys/{privkey,pubkey}_evm.pem)
           -o, --portable     generate portable EVM signatures
           -p, --pass         password for encrypted signing key
           -r, --recursive    recurse into directories (sign)
           -t, --type         file types to fix 'fdsxm' (f: file, d: directory, s: block/char/symlink)
                              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
               --engine e     preload OpenSSL engine e (such as: gost)
               --pcrs         file containing TPM pcrs, one per hash-algorithm/bank
               --ignore-violations ignore ToMToU measurement violations
               --verify-sig   verify the file signature based on the file hash, both
                              stored in the template data.
           -v                 increase verbosity level
           -h, --help         display this help and exit
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 two type 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).
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 1024
       Generate encrypted private key:
           openssl genrsa -des3 -out privkey_evm.pem 1024
       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 -sha1 -days 36500 -batch \
                       -x509 -config x509_evm.genkey \
                       -outform DER -out x509_evm.der -keyout privkey_evm.pem
       Configuration file x509_evm.genkey:
           # Begining of the file
           [ req ]
           default_bits = 1024
           distinguished_name = req_distinguished_name
           prompt = no
           string_mask = utf8only
           x509_extensions = myexts
           [ req_distinguished_name ]
           O = Magrathea
           CN = Glacier signing key
           emailAddress = slartibartfast AT magrathea.h2g2
           [ myexts ]
           basicConstraints=critical,CA:FALSE
           keyUsage=digitalSignature
           subjectKeyIdentifier=hash
           authorityKeyIdentifier=keyid
           # EOF
       Generate public key for using RSA key format:
           openssl rsa -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:
       o   Creation of local IMA certification authority (CA). It consist of
           private and public key certificate which are used to sign and
           verify other keys.
       o   Build Linux kernel with embedded local IMA CA X509 certificate. It
           is used to verify other keys added to the .ima trusted keyring
       o   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:
           # Begining 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
       Generate private key and X509 public key certificate:
           openssl req -new -x509 -utf8 -sha1 -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:
           # Begining of the file
           [ req ]
           default_bits = 1024
           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 -sha1 -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
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
AUTHOR
       Written by Dmitry Kasatkin, <dmitry.kasatkin at gmail.com> and others.
RESOURCES
           http://sourceforge.net/p/linux-ima/wiki/Home
           http://sourceforge.net/p/linux-ima/ima-evm-utils
COPYING
       Copyright (C) 2012 - 2014 Linux Integrity Project. Free use of this
       software is granted under the terms of the GNU Public License (GPL).
                                  04/08/2021                         EVMCTL(1)