Provided by: ima-evm-utils_1.1-0ubuntu1_amd64 bug

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_sign [--sigfile] [--key key] [--pass password] file
           ima_verify file
           ima_hash file
           ima_measurement [--key "key1, key2, ..."] [--list] 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
               --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
           -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@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:

       ·   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:

           # 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).

                                            04/01/2018                                  EVMCTL(1)