From 94e980cc45f2b21afceff0cb1866a1af32d20325 Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Fri, 23 Sep 2016 13:44:24 -0300 Subject: Documentation/module-signing.txt: convert to ReST markup - Fix identatio for the document title; - remove its index; - create a table for hash algorithm to be used; - use quote blocks where needed; - use monotonic fonts for parameters; - adjust whitespaces and blank lines; - Fix case on section titles; - add it to the user's book. Signed-off-by: Mauro Carvalho Chehab --- Documentation/module-signing.txt | 279 --------------------------------------- 1 file changed, 279 deletions(-) delete mode 100644 Documentation/module-signing.txt (limited to 'Documentation/module-signing.txt') diff --git a/Documentation/module-signing.txt b/Documentation/module-signing.txt deleted file mode 100644 index f0e3361..0000000 --- a/Documentation/module-signing.txt +++ /dev/null @@ -1,279 +0,0 @@ - ============================== - KERNEL MODULE SIGNING FACILITY - ============================== - -CONTENTS - - - Overview. - - Configuring module signing. - - Generating signing keys. - - Public keys in the kernel. - - Manually signing modules. - - Signed modules and stripping. - - Loading signed modules. - - Non-valid signatures and unsigned modules. - - Administering/protecting the private key. - - -======== -OVERVIEW -======== - -The kernel module signing facility cryptographically signs modules during -installation and then checks the signature upon loading the module. This -allows increased kernel security by disallowing the loading of unsigned modules -or modules signed with an invalid key. Module signing increases security by -making it harder to load a malicious module into the kernel. The module -signature checking is done by the kernel so that it is not necessary to have -trusted userspace bits. - -This facility uses X.509 ITU-T standard certificates to encode the public keys -involved. The signatures are not themselves encoded in any industrial standard -type. The facility currently only supports the RSA public key encryption -standard (though it is pluggable and permits others to be used). The possible -hash algorithms that can be used are SHA-1, SHA-224, SHA-256, SHA-384, and -SHA-512 (the algorithm is selected by data in the signature). - - -========================== -CONFIGURING MODULE SIGNING -========================== - -The module signing facility is enabled by going to the "Enable Loadable Module -Support" section of the kernel configuration and turning on - - CONFIG_MODULE_SIG "Module signature verification" - -This has a number of options available: - - (1) "Require modules to be validly signed" (CONFIG_MODULE_SIG_FORCE) - - This specifies how the kernel should deal with a module that has a - signature for which the key is not known or a module that is unsigned. - - If this is off (ie. "permissive"), then modules for which the key is not - available and modules that are unsigned are permitted, but the kernel will - be marked as being tainted, and the concerned modules will be marked as - tainted, shown with the character 'E'. - - If this is on (ie. "restrictive"), only modules that have a valid - signature that can be verified by a public key in the kernel's possession - will be loaded. All other modules will generate an error. - - Irrespective of the setting here, if the module has a signature block that - cannot be parsed, it will be rejected out of hand. - - - (2) "Automatically sign all modules" (CONFIG_MODULE_SIG_ALL) - - If this is on then modules will be automatically signed during the - modules_install phase of a build. If this is off, then the modules must - be signed manually using: - - scripts/sign-file - - - (3) "Which hash algorithm should modules be signed with?" - - This presents a choice of which hash algorithm the installation phase will - sign the modules with: - - CONFIG_MODULE_SIG_SHA1 "Sign modules with SHA-1" - CONFIG_MODULE_SIG_SHA224 "Sign modules with SHA-224" - CONFIG_MODULE_SIG_SHA256 "Sign modules with SHA-256" - CONFIG_MODULE_SIG_SHA384 "Sign modules with SHA-384" - CONFIG_MODULE_SIG_SHA512 "Sign modules with SHA-512" - - The algorithm selected here will also be built into the kernel (rather - than being a module) so that modules signed with that algorithm can have - their signatures checked without causing a dependency loop. - - - (4) "File name or PKCS#11 URI of module signing key" (CONFIG_MODULE_SIG_KEY) - - Setting this option to something other than its default of - "certs/signing_key.pem" will disable the autogeneration of signing keys - and allow the kernel modules to be signed with a key of your choosing. - The string provided should identify a file containing both a private key - and its corresponding X.509 certificate in PEM form, or — on systems where - the OpenSSL ENGINE_pkcs11 is functional — a PKCS#11 URI as defined by - RFC7512. In the latter case, the PKCS#11 URI should reference both a - certificate and a private key. - - If the PEM file containing the private key is encrypted, or if the - PKCS#11 token requries a PIN, this can be provided at build time by - means of the KBUILD_SIGN_PIN variable. - - - (5) "Additional X.509 keys for default system keyring" (CONFIG_SYSTEM_TRUSTED_KEYS) - - This option can be set to the filename of a PEM-encoded file containing - additional certificates which will be included in the system keyring by - default. - -Note that enabling module signing adds a dependency on the OpenSSL devel -packages to the kernel build processes for the tool that does the signing. - - -======================= -GENERATING SIGNING KEYS -======================= - -Cryptographic keypairs are required to generate and check signatures. A -private key is used to generate a signature and the corresponding public key is -used to check it. The private key is only needed during the build, after which -it can be deleted or stored securely. The public key gets built into the -kernel so that it can be used to check the signatures as the modules are -loaded. - -Under normal conditions, when CONFIG_MODULE_SIG_KEY is unchanged from its -default, the kernel build will automatically generate a new keypair using -openssl if one does not exist in the file: - - certs/signing_key.pem - -during the building of vmlinux (the public part of the key needs to be built -into vmlinux) using parameters in the: - - certs/x509.genkey - -file (which is also generated if it does not already exist). - -It is strongly recommended that you provide your own x509.genkey file. - -Most notably, in the x509.genkey file, the req_distinguished_name section -should be altered from the default: - - [ req_distinguished_name ] - #O = Unspecified company - CN = Build time autogenerated kernel key - #emailAddress = unspecified.user@unspecified.company - -The generated RSA key size can also be set with: - - [ req ] - default_bits = 4096 - - -It is also possible to manually generate the key private/public files using the -x509.genkey key generation configuration file in the root node of the Linux -kernel sources tree and the openssl command. The following is an example to -generate the public/private key files: - - openssl req -new -nodes -utf8 -sha256 -days 36500 -batch -x509 \ - -config x509.genkey -outform PEM -out kernel_key.pem \ - -keyout kernel_key.pem - -The full pathname for the resulting kernel_key.pem file can then be specified -in the CONFIG_MODULE_SIG_KEY option, and the certificate and key therein will -be used instead of an autogenerated keypair. - - -========================= -PUBLIC KEYS IN THE KERNEL -========================= - -The kernel contains a ring of public keys that can be viewed by root. They're -in a keyring called ".system_keyring" that can be seen by: - - [root@deneb ~]# cat /proc/keys - ... - 223c7853 I------ 1 perm 1f030000 0 0 keyring .system_keyring: 1 - 302d2d52 I------ 1 perm 1f010000 0 0 asymmetri Fedora kernel signing key: d69a84e6bce3d216b979e9505b3e3ef9a7118079: X509.RSA a7118079 [] - ... - -Beyond the public key generated specifically for module signing, additional -trusted certificates can be provided in a PEM-encoded file referenced by the -CONFIG_SYSTEM_TRUSTED_KEYS configuration option. - -Further, the architecture code may take public keys from a hardware store and -add those in also (e.g. from the UEFI key database). - -Finally, it is possible to add additional public keys by doing: - - keyctl padd asymmetric "" [.system_keyring-ID] <[key-file] - -e.g.: - - keyctl padd asymmetric "" 0x223c7853