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authorDavid S. Miller <davem@davemloft.net>2014-01-06 17:37:45 -0500
committerDavid S. Miller <davem@davemloft.net>2014-01-06 17:37:45 -0500
commit56a4342dfe3145cd66f766adccb28fd9b571606d (patch)
treed1593764488ff8cbb0b83cb9ae35fd968bf81760 /Documentation
parent805c1f4aedaba1bc8d839e7c27b128083dd5c2f0 (diff)
parentfe0d692bbc645786bce1a98439e548ae619269f5 (diff)
Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
Conflicts: drivers/net/ethernet/qlogic/qlcnic/qlcnic_sriov_pf.c net/ipv6/ip6_tunnel.c net/ipv6/ip6_vti.c ipv6 tunnel statistic bug fixes conflicting with consolidation into generic sw per-cpu net stats. qlogic conflict between queue counting bug fix and the addition of multiple MAC address support. Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/block/null_blk.txt72
-rw-r--r--Documentation/kernel-parameters.txt2
-rw-r--r--Documentation/module-signing.txt240
3 files changed, 314 insertions, 0 deletions
diff --git a/Documentation/block/null_blk.txt b/Documentation/block/null_blk.txt
new file mode 100644
index 000000000000..b2830b435895
--- /dev/null
+++ b/Documentation/block/null_blk.txt
@@ -0,0 +1,72 @@
1Null block device driver
2================================================================================
3
4I. Overview
5
6The null block device (/dev/nullb*) is used for benchmarking the various
7block-layer implementations. It emulates a block device of X gigabytes in size.
8The following instances are possible:
9
10 Single-queue block-layer
11 - Request-based.
12 - Single submission queue per device.
13 - Implements IO scheduling algorithms (CFQ, Deadline, noop).
14 Multi-queue block-layer
15 - Request-based.
16 - Configurable submission queues per device.
17 No block-layer (Known as bio-based)
18 - Bio-based. IO requests are submitted directly to the device driver.
19 - Directly accepts bio data structure and returns them.
20
21All of them have a completion queue for each core in the system.
22
23II. Module parameters applicable for all instances:
24
25queue_mode=[0-2]: Default: 2-Multi-queue
26 Selects which block-layer the module should instantiate with.
27
28 0: Bio-based.
29 1: Single-queue.
30 2: Multi-queue.
31
32home_node=[0--nr_nodes]: Default: NUMA_NO_NODE
33 Selects what CPU node the data structures are allocated from.
34
35gb=[Size in GB]: Default: 250GB
36 The size of the device reported to the system.
37
38bs=[Block size (in bytes)]: Default: 512 bytes
39 The block size reported to the system.
40
41nr_devices=[Number of devices]: Default: 2
42 Number of block devices instantiated. They are instantiated as /dev/nullb0,
43 etc.
44
45irq_mode=[0-2]: Default: 1-Soft-irq
46 The completion mode used for completing IOs to the block-layer.
47
48 0: None.
49 1: Soft-irq. Uses IPI to complete IOs across CPU nodes. Simulates the overhead
50 when IOs are issued from another CPU node than the home the device is
51 connected to.
52 2: Timer: Waits a specific period (completion_nsec) for each IO before
53 completion.
54
55completion_nsec=[ns]: Default: 10.000ns
56 Combined with irq_mode=2 (timer). The time each completion event must wait.
57
58submit_queues=[0..nr_cpus]:
59 The number of submission queues attached to the device driver. If unset, it
60 defaults to 1 on single-queue and bio-based instances. For multi-queue,
61 it is ignored when use_per_node_hctx module parameter is 1.
62
63hw_queue_depth=[0..qdepth]: Default: 64
64 The hardware queue depth of the device.
65
66III: Multi-queue specific parameters
67
68use_per_node_hctx=[0/1]: Default: 0
69 0: The number of submit queues are set to the value of the submit_queues
70 parameter.
71 1: The multi-queue block layer is instantiated with a hardware dispatch
72 queue for each CPU node in the system.
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 50680a59a2ff..b9e9bd854298 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1529,6 +1529,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
1529 1529
1530 * atapi_dmadir: Enable ATAPI DMADIR bridge support 1530 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1531 1531
1532 * disable: Disable this device.
1533
1532 If there are multiple matching configurations changing 1534 If there are multiple matching configurations changing
1533 the same attribute, the last one is used. 1535 the same attribute, the last one is used.
1534 1536
diff --git a/Documentation/module-signing.txt b/Documentation/module-signing.txt
new file mode 100644
index 000000000000..2b40e04d3c49
--- /dev/null
+++ b/Documentation/module-signing.txt
@@ -0,0 +1,240 @@
1 ==============================
2 KERNEL MODULE SIGNING FACILITY
3 ==============================
4
5CONTENTS
6
7 - Overview.
8 - Configuring module signing.
9 - Generating signing keys.
10 - Public keys in the kernel.
11 - Manually signing modules.
12 - Signed modules and stripping.
13 - Loading signed modules.
14 - Non-valid signatures and unsigned modules.
15 - Administering/protecting the private key.
16
17
18========
19OVERVIEW
20========
21
22The kernel module signing facility cryptographically signs modules during
23installation and then checks the signature upon loading the module. This
24allows increased kernel security by disallowing the loading of unsigned modules
25or modules signed with an invalid key. Module signing increases security by
26making it harder to load a malicious module into the kernel. The module
27signature checking is done by the kernel so that it is not necessary to have
28trusted userspace bits.
29
30This facility uses X.509 ITU-T standard certificates to encode the public keys
31involved. The signatures are not themselves encoded in any industrial standard
32type. The facility currently only supports the RSA public key encryption
33standard (though it is pluggable and permits others to be used). The possible
34hash algorithms that can be used are SHA-1, SHA-224, SHA-256, SHA-384, and
35SHA-512 (the algorithm is selected by data in the signature).
36
37
38==========================
39CONFIGURING MODULE SIGNING
40==========================
41
42The module signing facility is enabled by going to the "Enable Loadable Module
43Support" section of the kernel configuration and turning on
44
45 CONFIG_MODULE_SIG "Module signature verification"
46
47This has a number of options available:
48
49 (1) "Require modules to be validly signed" (CONFIG_MODULE_SIG_FORCE)
50
51 This specifies how the kernel should deal with a module that has a
52 signature for which the key is not known or a module that is unsigned.
53
54 If this is off (ie. "permissive"), then modules for which the key is not
55 available and modules that are unsigned are permitted, but the kernel will
56 be marked as being tainted.
57
58 If this is on (ie. "restrictive"), only modules that have a valid
59 signature that can be verified by a public key in the kernel's possession
60 will be loaded. All other modules will generate an error.
61
62 Irrespective of the setting here, if the module has a signature block that
63 cannot be parsed, it will be rejected out of hand.
64
65
66 (2) "Automatically sign all modules" (CONFIG_MODULE_SIG_ALL)
67
68 If this is on then modules will be automatically signed during the
69 modules_install phase of a build. If this is off, then the modules must
70 be signed manually using:
71
72 scripts/sign-file
73
74
75 (3) "Which hash algorithm should modules be signed with?"
76
77 This presents a choice of which hash algorithm the installation phase will
78 sign the modules with:
79
80 CONFIG_SIG_SHA1 "Sign modules with SHA-1"
81 CONFIG_SIG_SHA224 "Sign modules with SHA-224"
82 CONFIG_SIG_SHA256 "Sign modules with SHA-256"
83 CONFIG_SIG_SHA384 "Sign modules with SHA-384"
84 CONFIG_SIG_SHA512 "Sign modules with SHA-512"
85
86 The algorithm selected here will also be built into the kernel (rather
87 than being a module) so that modules signed with that algorithm can have
88 their signatures checked without causing a dependency loop.
89
90
91=======================
92GENERATING SIGNING KEYS
93=======================
94
95Cryptographic keypairs are required to generate and check signatures. A
96private key is used to generate a signature and the corresponding public key is
97used to check it. The private key is only needed during the build, after which
98it can be deleted or stored securely. The public key gets built into the
99kernel so that it can be used to check the signatures as the modules are
100loaded.
101
102Under normal conditions, the kernel build will automatically generate a new
103keypair using openssl if one does not exist in the files:
104
105 signing_key.priv
106 signing_key.x509
107
108during the building of vmlinux (the public part of the key needs to be built
109into vmlinux) using parameters in the:
110
111 x509.genkey
112
113file (which is also generated if it does not already exist).
114
115It is strongly recommended that you provide your own x509.genkey file.
116
117Most notably, in the x509.genkey file, the req_distinguished_name section
118should be altered from the default:
119
120 [ req_distinguished_name ]
121 O = Magrathea
122 CN = Glacier signing key
123 emailAddress = slartibartfast@magrathea.h2g2
124
125The generated RSA key size can also be set with:
126
127 [ req ]
128 default_bits = 4096
129
130
131It is also possible to manually generate the key private/public files using the
132x509.genkey key generation configuration file in the root node of the Linux
133kernel sources tree and the openssl command. The following is an example to
134generate the public/private key files:
135
136 openssl req -new -nodes -utf8 -sha256 -days 36500 -batch -x509 \
137 -config x509.genkey -outform DER -out signing_key.x509 \
138 -keyout signing_key.priv
139
140
141=========================
142PUBLIC KEYS IN THE KERNEL
143=========================
144
145The kernel contains a ring of public keys that can be viewed by root. They're
146in a keyring called ".system_keyring" that can be seen by:
147
148 [root@deneb ~]# cat /proc/keys
149 ...
150 223c7853 I------ 1 perm 1f030000 0 0 keyring .system_keyring: 1
151 302d2d52 I------ 1 perm 1f010000 0 0 asymmetri Fedora kernel signing key: d69a84e6bce3d216b979e9505b3e3ef9a7118079: X509.RSA a7118079 []
152 ...
153
154Beyond the public key generated specifically for module signing, any file
155placed in the kernel source root directory or the kernel build root directory
156whose name is suffixed with ".x509" will be assumed to be an X.509 public key
157and will be added to the keyring.
158
159Further, the architecture code may take public keys from a hardware store and
160add those in also (e.g. from the UEFI key database).
161
162Finally, it is possible to add additional public keys by doing:
163
164 keyctl padd asymmetric "" [.system_keyring-ID] <[key-file]
165
166e.g.:
167
168 keyctl padd asymmetric "" 0x223c7853 <my_public_key.x509
169
170Note, however, that the kernel will only permit keys to be added to
171.system_keyring _if_ the new key's X.509 wrapper is validly signed by a key
172that is already resident in the .system_keyring at the time the key was added.
173
174
175=========================
176MANUALLY SIGNING MODULES
177=========================
178
179To manually sign a module, use the scripts/sign-file tool available in
180the Linux kernel source tree. The script requires 4 arguments:
181
182 1. The hash algorithm (e.g., sha256)
183 2. The private key filename
184 3. The public key filename
185 4. The kernel module to be signed
186
187The following is an example to sign a kernel module:
188
189 scripts/sign-file sha512 kernel-signkey.priv \
190 kernel-signkey.x509 module.ko
191
192The hash algorithm used does not have to match the one configured, but if it
193doesn't, you should make sure that hash algorithm is either built into the
194kernel or can be loaded without requiring itself.
195
196
197============================
198SIGNED MODULES AND STRIPPING
199============================
200
201A signed module has a digital signature simply appended at the end. The string
202"~Module signature appended~." at the end of the module's file confirms that a
203signature is present but it does not confirm that the signature is valid!
204
205Signed modules are BRITTLE as the signature is outside of the defined ELF
206container. Thus they MAY NOT be stripped once the signature is computed and
207attached. Note the entire module is the signed payload, including any and all
208debug information present at the time of signing.
209
210
211======================
212LOADING SIGNED MODULES
213======================
214
215Modules are loaded with insmod, modprobe, init_module() or finit_module(),
216exactly as for unsigned modules as no processing is done in userspace. The
217signature checking is all done within the kernel.
218
219
220=========================================
221NON-VALID SIGNATURES AND UNSIGNED MODULES
222=========================================
223
224If CONFIG_MODULE_SIG_FORCE is enabled or enforcemodulesig=1 is supplied on
225the kernel command line, the kernel will only load validly signed modules
226for which it has a public key. Otherwise, it will also load modules that are
227unsigned. Any module for which the kernel has a key, but which proves to have
228a signature mismatch will not be permitted to load.
229
230Any module that has an unparseable signature will be rejected.
231
232
233=========================================
234ADMINISTERING/PROTECTING THE PRIVATE KEY
235=========================================
236
237Since the private key is used to sign modules, viruses and malware could use
238the private key to sign modules and compromise the operating system. The
239private key must be either destroyed or moved to a secure location and not kept
240in the root node of the kernel source tree.