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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@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).
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