[PATCH 7/7] dm: add documentation for IMA measurement support

[Tushar Sugandhi <tusharsu@linux.microsoft.com>]

To interpret various DM target measurement data in IMA logs,
a separate documentation page is needed under
Documentation/admin-guide/device-mapper.

Add documentation to help system administrators and attestation
client/server component owners to interpret the measurement
data generated by various DM targets, on various device/table state
changes.

Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
---
 .../admin-guide/device-mapper/dm-ima.rst      | 306 ++++++++++++++++++
 .../admin-guide/device-mapper/index.rst       |   1 +
 2 files changed, 307 insertions(+)
 create mode 100644 Documentation/admin-guide/device-mapper/dm-ima.rst

diff --git a/Documentation/admin-guide/device-mapper/dm-ima.rst b/Documentation/admin-guide/device-mapper/dm-ima.rst
new file mode 100644
index 000000000000..1be2da7c6b6b
--- /dev/null
+++ b/Documentation/admin-guide/device-mapper/dm-ima.rst
@@ -0,0 +1,306 @@
+======
+dm-ima
+======
+
+For a given system, various external services/infrastructure tools
+(including the attestation service) interact with it - both during the
+setup and during rest of the system run-time.  They share sensitive data
+and/or execute critical workload on that system.  The external services
+may want to verify the current run-time state of the relevant kernel
+subsystems before fully trusting the system with business-critical
+data/workload.
+
+Device mapper plays a critical role on a given system by providing
+various important functionalities to the block devices using various
+target types like crypt, verity, integrity etc.  Each of these target
+types’ functionalities can be configured with various attributes.
+The attributes chosen to configure these target types can significantly
+impact the security profile of the block device, and in-turn, of the
+system itself.  For instance, the type of encryption algorithm and the
+key size determines the strength of encryption for a given block device.
+
+Therefore, verifying the current state of various block devices as well
+as their various target attributes is crucial for external services before
+fully trusting the system with business-critical data/workload.
+
+IMA kernel subsystem provides the necessary functionality for
+device mapper to measure the state and configuration of
+various block devices -
+  - BY device mapper itself, from within the kernel,
+  - in a tamper resistant way,
+  - and re-measured - triggered on state/configuration change.
+
+Setting the IMA Policy:
+=======================
+For IMA to measure the data on a given system, the IMA policy on the
+system needs to be updated to have following line, and the system needs
+to be restarted for the measurements to take effect.
+
+/etc/ima/ima-policy
+ measure func=CRITICAL_DATA label=device-mapper template=ima-buf
+
+The measurements will be reflected in the IMA logs, which are located at:
+
+/sys/kernel/security/integrity/ima/ascii_runtime_measurements
+/sys/kernel/security/integrity/ima/binary_runtime_measurements
+
+Then IMA ASCII measurement log has the following format:
+PCR TEMPLATE_DIGEST TEMPLATE ALG:EVENT_DIGEST EVENT_NAME EVENT_DATA
+
+PCR := Platform Configuration Register, in which the values are registered.
+       This is applicable if TPM chip is in use.
+TEMPLATE_DIGEST := Template digest of the IMA record.
+TEMPLATE := Template that registered the integrity value (e.g. ima-buf).
+ALG:EVENT_DIGEST = Algorithm to compute event digest, followed by digest of event data
+EVENT_NAME := Description of the event (e.g. 'table_load').
+EVENT_DATA := The event data to be measured.
+
+The DM target data measured by IMA subsystem can alternatively
+be queried from userspace by setting DM_IMA_MEASUREMENT_FLAG with
+DM_TABLE_STATUS_CMD.
+
+Supported Device States:
+========================
+Following device state changes will trigger IMA measurements.
+01. Table load
+02. Device resume
+03. Device remove
+04. Table clear
+05. Device rename
+
+01. Table load:
+---------------
+When a new table is loaded in a device's inactive table slot,
+the device information and target specific details from the
+targets in the table are measured.
+
+For instance, if a linear device is created with the following table entries,
+# dmsetup create linear1
+0 2 linear /dev/loop0 512
+2 2 linear /dev/loop0 512
+4 2 linear /dev/loop0 512
+6 2 linear /dev/loop0 512
+
+Then IMA ASCII measurement log will have an entry with:
+EVENT_NAME := table_load
+EVENT_DATA := [device_data];[target_data_row_1];[target_data_row_2];...[target_data_row_n];
+
+E.g.
+(converted from ASCII to text for readability)
+10 a8c5ff755561c7a28146389d1514c318592af49a ima-buf sha256:4d73481ecce5eadba8ab084640d85bb9ca899af4d0a122989252a76efadc5b72
+table_load
+name=linear1,uuid=,major=253,minor=0,minor_count=1,num_targets=4;
+target_index=0,target_begin=0,target_len=2,target_type_name=linear,target_type_version=1.4.0,device_name=7:0,start=512;
+target_index=1,target_begin=2,target_len=2,target_type_name=linear,target_type_version=1.4.0,device_name=7:0,start=512;
+target_index=2,target_begin=4,target_len=2,target_type_name=linear,target_type_version=1.4.0,device_name=7:0,start=512;
+target_index=3,target_begin=6,target_len=2,target_type_name=linear,target_type_version=1.4.0,device_name=7:0,start=512;
+
+02. Device resume:
+------------------
+When a suspended device is resumed, the device information and a sha256 hash of the
+data from previous load of an active table are measured.
+
+For instance, if a linear device is resumed with the following command,
+#dmsetup resume linear1
+
+Then IMA ASCII measurement log will have an entry with:
+EVENT_NAME := device_resume
+EVENT_DATA := [device_data];active_table_hash=(sha256hash([device_data];[target_data_row_1];...[target_data_row_n]);
+              current_device_capacity=<N>;
+
+E.g.
+(converted from ASCII to text for readability)
+10 56c00cc062ffc24ccd9ac2d67d194af3282b934e ima-buf sha256:e7d12c03b958b4e0e53e7363a06376be88d98a1ac191fdbd3baf5e4b77f329b6
+device_resume
+name=linear1,uuid=,major=253,minor=0,minor_count=1,num_targets=4;
+active_table_hash=4d73481ecce5eadba8ab084640d85bb9ca899af4d0a122989252a76efadc5b72;current_device_capacity=8;
+
+03. Device remove:
+------------------
+When a device is removed, the device information and a sha256 hash of the
+data from an active and inactive table are measured.
+
+For instance, if a linear device is removed with the following command,
+# dmsetup remove linear1
+
+Then IMA ASCII measurement log will have an entry with:
+EVENT_NAME := device_remove
+EVENT_DATA := [device_active_metadata];[device_inactive_metadata];
+              [active_table_hash=(sha256hash([device_active_metadata];[active_table_row_1];...[active_table_row_n]),
+              [inactive_table_hash=(sha256hash([device_inactive_metadata];[inactive_table_row_1];...[inactive_table_row_n]),
+              remove_all=[y|n];current_device_capacity=<N>;
+
+E.g
+(converted from ASCII to text for readability)
+10 499812b621b705061c4514d643894483e16d2619 ima-buf sha256:c3f26b02f09bf5b464925589454bdd4d354077ce430fd1e75c9e96ce29cd1cad
+device_remove
+device_active_metadata=name=linear1,uuid=,major=253,minor=0,minor_count=1,num_targets=4;
+device_inactive_metadata=name=linear1,uuid=,major=253,minor=0,minor_count=1,num_targets=2;
+active_table_hash=4d73481ecce5eadba8ab084640d85bb9ca899af4d0a122989252a76efadc5b72,
+inactive_table_hash=5596cc857b0e887fd0c5d58dc6382513284596b07f09fd37efae2da224bd521d,remove_all=n;
+current_device_capacity=8;
+
+
+04. Table clear:
+----------------
+When an inactive table is cleared from the device, the device information and a sha256 hash of the
+data from an inactive table are measured.
+
+For instance, if a linear device's inactive table is cleared with the following command,
+
+# dmsetup clear linear1
+
+Then IMA ASCII measurement log will have an entry with:
+EVENT_NAME := table_clear
+EVENT_DATA := [device_data];inactive_table_hash=(sha256hash([device_data];[inactive_table_row_1];...[inactive_table_row_n]);
+current_device_capacity=<N>;
+
+E.g.
+(converted from ASCII to text for readability)
+10 9c11e284d792875352d51c09f6643c96649484be ima-buf sha256:84b22b364ea4d8264fa33c38635c18ef448fa9077731fa7e5f969b1da2003ea4
+table_clear
+name=linear1,uuid=,major=253,minor=0,minor_count=1,num_targets=2;
+inactive_table_hash=5596cc857b0e887fd0c5d58dc6382513284596b07f09fd37efae2da224bd521d;current_device_capacity=0;
+
+
+05. Device rename:
+------------------
+When an device's NAME or UUID is changed, the device information and the new NAME and UUID
+are measured.
+
+For instance, if a linear device's name is changed with the following command,
+
+#dmsetup rename linear1 linear=2
+Then IMA ASCII measurement log will have an entry with:
+EVENT_NAME := device_rename
+EVENT_DATA := [current_device_data];new_name=<new_name_value>;new_uuid=<new_uuid_value>;current_device_capacity=<N>;
+
+E.g 1:
+#dmsetup rename linear1 --setuuid 1234-5678
+
+IMA Log entry:
+(converted from ASCII to text for readability)
+10 7380ef4d1349fe1ebd74affa54e9fcc960e3cbf5 ima-buf sha256:9759e36a17a967ea43c1bf3455279395a40bd0401105ec5ad8edb9a52054efc7
+device_rename
+name=linear1,uuid=,major=253,minor=0,minor_count=1,num_targets=1;new_name=linear1,new_uuid=1234-5678;current_device_capacity=2;
+
+E.g 2:
+# dmsetup rename linear1 linear=2
+10 092c8266fc36e44f74c59f123ecfe15310f249f4 ima-buf sha256:4cf8b85c81fa6fedaeb602b05019124dbbb0605dce58fcdeea56887a8a3874cd
+device_rename
+name=linear1,uuid=1234-5678,major=253,minor=0,minor_count=1,num_targets=1;new_name=linear\=2,new_uuid=1234-5678;current_device_capacity=2;
+
+
+Supported targets:
+==================
+Following targets are supported to measure their data using IMA.
+
+01. cache
+02. crypt
+03. integrity
+04. linear
+05. mirror
+06. multipath
+07. raid
+08. snapshot
+09. striped
+10. verity
+
+01. cache
+---------
+<<documenatation in progress>>
+
+02. crypt
+-----
+When a crypt target is loaded, then IMA ASCII measurement log will have an entry
+similar to the following, depicting what crypt attributes are measured in EVENT_DATA.
+
+(converted from ASCII to text for readability)
+10 fe3b80a35b155bd282df778e2625066c05fc068c ima-buf sha256:2d86ce9d6f16a4a97607318aa123ae816e0ceadefeea7903abf7f782f2cb78ad
+table_load
+name=test-crypt,uuid=,major=253,minor=0,minor_count=1,num_targets=1;
+target_index=0,target_begin=0,target_len=1953125,target_type_name=crypt,target_type_version=1.23.0,
+allow_discards=y,same_cpu=n,submit_from_crypt_cpus=n,no_read_workqueue=n,no_write_workqueue=n,
+iv_large_sectors=n,cipher_string=aes-xts-plain64,key_size=32,key_parts=1,key_extra_size=0,key_mac_size=0;
+
+03. integrity
+-------------
+<<documenatation in progress>>
+
+
+04. linear
+----------
+When a linear target is loaded, then IMA ASCII measurement log will have an entry
+similar to the following, depicting what linear attributes are measured in EVENT_DATA.
+
+(converted from ASCII to text for readability)
+10 a8c5ff755561c7a28146389d1514c318592af49a ima-buf sha256:4d73481ecce5eadba8ab084640d85bb9ca899af4d0a122989252a76efadc5b72
+table_load
+name=linear1,uuid=,major=253,minor=0,minor_count=1,num_targets=4;
+target_index=0,target_begin=0,target_len=2,target_type_name=linear,target_type_version=1.4.0,device_name=7:0,start=512;
+target_index=1,target_begin=2,target_len=2,target_type_name=linear,target_type_version=1.4.0,device_name=7:0,start=512;
+target_index=2,target_begin=4,target_len=2,target_type_name=linear,target_type_version=1.4.0,device_name=7:0,start=512;
+target_index=3,target_begin=6,target_len=2,target_type_name=linear,target_type_version=1.4.0,device_name=7:0,start=512;
+
+05. mirror
+----------
+When a mirror target is loaded, then IMA ASCII measurement log will have an entry
+similar to the following, depicting what mirror attributes are measured in EVENT_DATA.
+
+(converted from ASCII to text for readability)
+10 90ff9113a00c367df823595dc347425ce3bfc50a ima-buf sha256:8da0678ed3bf616533573d9e61e5342f2bd16cb0b3145a08262641a743806c2e
+table_load
+name=test-mirror,uuid=,major=253,minor=4,minor_count=1,num_targets=1;
+target_index=0,target_begin=0,target_len=1953125,target_type_name=mirror,target_type_version=1.14.0,
+mirrors=2,mirror_device_0=253:2,mirror_device_0_status=A,mirror_device_1=253:3,mirror_device_1_status=A,
+handle_errors=y,keep_log=n,log_type_status=;
+
+06. multipath
+-------------
+<<documenatation in progress>>
+
+07. raid
+--------
+When a raid target is loaded, then IMA ASCII measurement log will have an entry
+similar to the following, depicting what raid attributes are measured in EVENT_DATA.
+
+(converted from ASCII to text for readability)
+10 76cb30d0cd0fe099966f20f5c82e3a2ac29b21a0 ima-buf sha256:52250f20b27376fcfb348bdfa1e1cf5acfd6646e0f3ad1a72952cffd9f818753
+table_load
+name=test-raid1,uuid=,major=253,minor=2,minor_count=1,num_targets=1;
+target_index=0,target_begin=0,target_len=1953125,target_type_name=raid,target_type_version=1.15.1,
+raid_type=raid1,raid_disks=2,raid_state=idle,raid_device_0_status=A,raid_device_1_status=A;
+
+08. snapshot
+------------
+<<documenatation in progress>>
+
+09. striped
+----------
+When a linear target is loaded, then IMA ASCII measurement log will have an entry
+similar to the following, depicting what linear attributes are measured in EVENT_DATA.
+
+(converted from ASCII to text for readability)
+10 7bd94fa8f799169b9f12d97b9dbdce4dc5509233 ima-buf sha256:0d148eda69887f7833f1a6042767b54359cd23b64fa941b9e1856879eee1f778
+table_load
+name=test-raid0,uuid=,major=253,minor=8,minor_count=1,num_targets=1;
+target_index=0,target_begin=0,target_len=7812096,target_type_name=striped,target_type_version=1.6.0,stripes=4,chunk_size=128,
+stripe_0_device_name=253:1,stripe_0_physical_start=0,stripe_0_status=A,
+stripe_1_device_name=253:3,stripe_1_physical_start=0,stripe_1_status=A,
+stripe_2_device_name=253:5,stripe_2_physical_start=0,stripe_2_status=A,
+stripe_3_device_name=253:7,stripe_3_physical_start=0,stripe_3_status=A;
+
+10. verity
+----------
+When a verity target is loaded, then IMA ASCII measurement log will have an entry
+similar to the following, depicting what verity attributes are measured in EVENT_DATA.
+
+(converted from ASCII to text for readability)
+10 fced5f575b140fc0efac302c88a635174cd663da ima-buf sha256:021370c1cc93929460b06922c606334fb1d7ea5ecf04f2384f3157a446894283
+table_load
+name=test-verity,uuid=,major=253,minor=2,minor_count=1,num_targets=1;
+target_index=0,target_begin=0,target_len=1953120,target_type_name=verity,target_type_version=1.8.0,hash_failed=V,
+verity_version=1,data_device_name=253:1,hash_device_name=253:0,verity_algorithm=sha256,
+root_digest=29cb87e60ce7b12b443ba6008266f3e41e93e403d7f298f8e3f316b29ff89c5e,
+salt=e48da609055204e89ae53b655ca2216dd983cf3cb829f34f63a297d106d53e2d,
+ignore_zero_blocks=n,check_at_most_once=n;
diff --git a/Documentation/admin-guide/device-mapper/index.rst b/Documentation/admin-guide/device-mapper/index.rst
index 6cf8adc86fa8..cde52cc09645 100644
--- a/Documentation/admin-guide/device-mapper/index.rst
+++ b/Documentation/admin-guide/device-mapper/index.rst
@@ -13,6 +13,7 @@ Device Mapper
     dm-dust
     dm-ebs
     dm-flakey
+    dm-ima
     dm-init
     dm-integrity
     dm-io
-- 
2.25.1