diff options
Diffstat (limited to 'Documentation/admin-guide/LSM')
| -rw-r--r-- | Documentation/admin-guide/LSM/apparmor.rst | 7 | ||||
| -rw-r--r-- | Documentation/admin-guide/LSM/index.rst | 2 | ||||
| -rw-r--r-- | Documentation/admin-guide/LSM/ipe.rst | 824 | ||||
| -rw-r--r-- | Documentation/admin-guide/LSM/landlock.rst | 158 | ||||
| -rw-r--r-- | Documentation/admin-guide/LSM/tomoyo.rst | 35 |
5 files changed, 1000 insertions, 26 deletions
diff --git a/Documentation/admin-guide/LSM/apparmor.rst b/Documentation/admin-guide/LSM/apparmor.rst index 6cf81bbd7ce8..47939ee89d74 100644 --- a/Documentation/admin-guide/LSM/apparmor.rst +++ b/Documentation/admin-guide/LSM/apparmor.rst @@ -18,8 +18,11 @@ set ``CONFIG_SECURITY_APPARMOR=y`` If AppArmor should be selected as the default security module then set:: - CONFIG_DEFAULT_SECURITY="apparmor" - CONFIG_SECURITY_APPARMOR_BOOTPARAM_VALUE=1 + CONFIG_DEFAULT_SECURITY_APPARMOR=y + +The CONFIG_LSM parameter manages the order and selection of LSMs. +Specify apparmor as the first "major" module (e.g. AppArmor, SELinux, Smack) +in the list. Build the kernel diff --git a/Documentation/admin-guide/LSM/index.rst b/Documentation/admin-guide/LSM/index.rst index a6ba95fbaa9f..b44ef68f6e4d 100644 --- a/Documentation/admin-guide/LSM/index.rst +++ b/Documentation/admin-guide/LSM/index.rst @@ -47,3 +47,5 @@ subdirectories. tomoyo Yama SafeSetID + ipe + landlock diff --git a/Documentation/admin-guide/LSM/ipe.rst b/Documentation/admin-guide/LSM/ipe.rst new file mode 100644 index 000000000000..dc7088451f9d --- /dev/null +++ b/Documentation/admin-guide/LSM/ipe.rst @@ -0,0 +1,824 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Integrity Policy Enforcement (IPE) +================================== + +.. NOTE:: + + This is the documentation for admins, system builders, or individuals + attempting to use IPE. If you're looking for more developer-focused + documentation about IPE please see :doc:`the design docs </security/ipe>`. + +Overview +-------- + +Integrity Policy Enforcement (IPE) is a Linux Security Module that takes a +complementary approach to access control. Unlike traditional access control +mechanisms that rely on labels and paths for decision-making, IPE focuses +on the immutable security properties inherent to system components. These +properties are fundamental attributes or features of a system component +that cannot be altered, ensuring a consistent and reliable basis for +security decisions. + +To elaborate, in the context of IPE, system components primarily refer to +files or the devices these files reside on. However, this is just a +starting point. The concept of system components is flexible and can be +extended to include new elements as the system evolves. The immutable +properties include the origin of a file, which remains constant and +unchangeable over time. For example, IPE policies can be crafted to trust +files originating from the initramfs. Since initramfs is typically verified +by the bootloader, its files are deemed trustworthy; "file is from +initramfs" becomes an immutable property under IPE's consideration. + +The immutable property concept extends to the security features enabled on +a file's origin, such as dm-verity or fs-verity, which provide a layer of +integrity and trust. For example, IPE allows the definition of policies +that trust files from a dm-verity protected device. dm-verity ensures the +integrity of an entire device by providing a verifiable and immutable state +of its contents. Similarly, fs-verity offers filesystem-level integrity +checks, allowing IPE to enforce policies that trust files protected by +fs-verity. These two features cannot be turned off once established, so +they are considered immutable properties. These examples demonstrate how +IPE leverages immutable properties, such as a file's origin and its +integrity protection mechanisms, to make access control decisions. + +For the IPE policy, specifically, it grants the ability to enforce +stringent access controls by assessing security properties against +reference values defined within the policy. This assessment can be based on +the existence of a security property (e.g., verifying if a file originates +from initramfs) or evaluating the internal state of an immutable security +property. The latter includes checking the roothash of a dm-verity +protected device, determining whether dm-verity possesses a valid +signature, assessing the digest of a fs-verity protected file, or +determining whether fs-verity possesses a valid built-in signature. This +nuanced approach to policy enforcement enables a highly secure and +customizable system defense mechanism, tailored to specific security +requirements and trust models. + +To enable IPE, ensure that ``CONFIG_SECURITY_IPE`` (under +:menuselection:`Security -> Integrity Policy Enforcement (IPE)`) config +option is enabled. + +Use Cases +--------- + +IPE works best in fixed-function devices: devices in which their purpose +is clearly defined and not supposed to be changed (e.g. network firewall +device in a data center, an IoT device, etcetera), where all software and +configuration is built and provisioned by the system owner. + +IPE is a long-way off for use in general-purpose computing: the Linux +community as a whole tends to follow a decentralized trust model (known as +the web of trust), which IPE has no support for it yet. Instead, IPE +supports PKI (public key infrastructure), which generally designates a +set of trusted entities that provide a measure of absolute trust. + +Additionally, while most packages are signed today, the files inside +the packages (for instance, the executables), tend to be unsigned. This +makes it difficult to utilize IPE in systems where a package manager is +expected to be functional, without major changes to the package manager +and ecosystem behind it. + +The digest_cache LSM [#digest_cache_lsm]_ is a system that when combined with IPE, +could be used to enable and support general-purpose computing use cases. + +Known Limitations +----------------- + +IPE cannot verify the integrity of anonymous executable memory, such as +the trampolines created by gcc closures and libffi (<3.4.2), or JIT'd code. +Unfortunately, as this is dynamically generated code, there is no way +for IPE to ensure the integrity of this code to form a trust basis. + +IPE cannot verify the integrity of programs written in interpreted +languages when these scripts are invoked by passing these program files +to the interpreter. This is because the way interpreters execute these +files; the scripts themselves are not evaluated as executable code +through one of IPE's hooks, but they are merely text files that are read +(as opposed to compiled executables) [#interpreters]_. + +Threat Model +------------ + +IPE specifically targets the risk of tampering with user-space executable +code after the kernel has initially booted, including the kernel modules +loaded from userspace via ``modprobe`` or ``insmod``. + +To illustrate, consider a scenario where an untrusted binary, possibly +malicious, is downloaded along with all necessary dependencies, including a +loader and libc. The primary function of IPE in this context is to prevent +the execution of such binaries and their dependencies. + +IPE achieves this by verifying the integrity and authenticity of all +executable code before allowing them to run. It conducts a thorough +check to ensure that the code's integrity is intact and that they match an +authorized reference value (digest, signature, etc) as per the defined +policy. If a binary does not pass this verification process, either +because its integrity has been compromised or it does not meet the +authorization criteria, IPE will deny its execution. Additionally, IPE +generates audit logs which may be utilized to detect and analyze failures +resulting from policy violation. + +Tampering threat scenarios include modification or replacement of +executable code by a range of actors including: + +- Actors with physical access to the hardware +- Actors with local network access to the system +- Actors with access to the deployment system +- Compromised internal systems under external control +- Malicious end users of the system +- Compromised end users of the system +- Remote (external) compromise of the system + +IPE does not mitigate threats arising from malicious but authorized +developers (with access to a signing certificate), or compromised +developer tools used by them (i.e. return-oriented programming attacks). +Additionally, IPE draws hard security boundary between userspace and +kernelspace. As a result, kernel-level exploits are considered outside +the scope of IPE and mitigation is left to other mechanisms. + +Policy +------ + +IPE policy is a plain-text [#devdoc]_ policy composed of multiple statements +over several lines. There is one required line, at the top of the +policy, indicating the policy name, and the policy version, for +instance:: + + policy_name=Ex_Policy policy_version=0.0.0 + +The policy name is a unique key identifying this policy in a human +readable name. This is used to create nodes under securityfs as well as +uniquely identify policies to deploy new policies vs update existing +policies. + +The policy version indicates the current version of the policy (NOT the +policy syntax version). This is used to prevent rollback of policy to +potentially insecure previous versions of the policy. + +The next portion of IPE policy are rules. Rules are formed by key=value +pairs, known as properties. IPE rules require two properties: ``action``, +which determines what IPE does when it encounters a match against the +rule, and ``op``, which determines when the rule should be evaluated. +The ordering is significant, a rule must start with ``op``, and end with +``action``. Thus, a minimal rule is:: + + op=EXECUTE action=ALLOW + +This example will allow any execution. Additional properties are used to +assess immutable security properties about the files being evaluated. +These properties are intended to be descriptions of systems within the +kernel that can provide a measure of integrity verification, such that IPE +can determine the trust of the resource based on the value of the property. + +Rules are evaluated top-to-bottom. As a result, any revocation rules, +or denies should be placed early in the file to ensure that these rules +are evaluated before a rule with ``action=ALLOW``. + +IPE policy supports comments. The character '#' will function as a +comment, ignoring all characters to the right of '#' until the newline. + +The default behavior of IPE evaluations can also be expressed in policy, +through the ``DEFAULT`` statement. This can be done at a global level, +or a per-operation level:: + + # Global + DEFAULT action=ALLOW + + # Operation Specific + DEFAULT op=EXECUTE action=ALLOW + +A default must be set for all known operations in IPE. If you want to +preserve older policies being compatible with newer kernels that can introduce +new operations, set a global default of ``ALLOW``, then override the +defaults on a per-operation basis (as above). + +With configurable policy-based LSMs, there's several issues with +enforcing the configurable policies at startup, around reading and +parsing the policy: + +1. The kernel *should* not read files from userspace, so directly reading + the policy file is prohibited. +2. The kernel command line has a character limit, and one kernel module + should not reserve the entire character limit for its own + configuration. +3. There are various boot loaders in the kernel ecosystem, so handing + off a memory block would be costly to maintain. + +As a result, IPE has addressed this problem through a concept of a "boot +policy". A boot policy is a minimal policy which is compiled into the +kernel. This policy is intended to get the system to a state where +userspace is set up and ready to receive commands, at which point a more +complex policy can be deployed via securityfs. The boot policy can be +specified via ``SECURITY_IPE_BOOT_POLICY`` config option, which accepts +a path to a plain-text version of the IPE policy to apply. This policy +will be compiled into the kernel. If not specified, IPE will be disabled +until a policy is deployed and activated through securityfs. + +Deploying Policies +~~~~~~~~~~~~~~~~~~ + +Policies can be deployed from userspace through securityfs. These policies +are signed through the PKCS#7 message format to enforce some level of +authorization of the policies (prohibiting an attacker from gaining +unconstrained root, and deploying an "allow all" policy). These +policies must be signed by a certificate that chains to the +``SYSTEM_TRUSTED_KEYRING``, or to the secondary and/or platform keyrings if +``CONFIG_IPE_POLICY_SIG_SECONDARY_KEYRING`` and/or +``CONFIG_IPE_POLICY_SIG_PLATFORM_KEYRING`` are enabled, respectively. +With openssl, the policy can be signed by:: + + openssl smime -sign \ + -in "$MY_POLICY" \ + -signer "$MY_CERTIFICATE" \ + -inkey "$MY_PRIVATE_KEY" \ + -noattr \ + -nodetach \ + -nosmimecap \ + -outform der \ + -out "$MY_POLICY.p7b" + +Deploying the policies is done through securityfs, through the +``new_policy`` node. To deploy a policy, simply cat the file into the +securityfs node:: + + cat "$MY_POLICY.p7b" > /sys/kernel/security/ipe/new_policy + +Upon success, this will create one subdirectory under +``/sys/kernel/security/ipe/policies/``. The subdirectory will be the +``policy_name`` field of the policy deployed, so for the example above, +the directory will be ``/sys/kernel/security/ipe/policies/Ex_Policy``. +Within this directory, there will be seven files: ``pkcs7``, ``policy``, +``name``, ``version``, ``active``, ``update``, and ``delete``. + +The ``pkcs7`` file is read-only. Reading it returns the raw PKCS#7 data +that was provided to the kernel, representing the policy. If the policy being +read is the boot policy, this will return ``ENOENT``, as it is not signed. + +The ``policy`` file is read only. Reading it returns the PKCS#7 inner +content of the policy, which will be the plain text policy. + +The ``active`` file is used to set a policy as the currently active policy. +This file is rw, and accepts a value of ``"1"`` to set the policy as active. +Since only a single policy can be active at one time, all other policies +will be marked inactive. The policy being marked active must have a policy +version greater or equal to the currently-running version. + +The ``update`` file is used to update a policy that is already present +in the kernel. This file is write-only and accepts a PKCS#7 signed +policy. Two checks will always be performed on this policy: First, the +``policy_names`` must match with the updated version and the existing +version. Second the updated policy must have a policy version greater than +the currently-running version. This is to prevent rollback attacks. + +The ``delete`` file is used to remove a policy that is no longer needed. +This file is write-only and accepts a value of ``1`` to delete the policy. +On deletion, the securityfs node representing the policy will be removed. +However, delete the current active policy is not allowed and will return +an operation not permitted error. + +Similarly, writing to both ``update`` and ``new_policy`` could result in +bad message(policy syntax error) or file exists error. The latter error happens +when trying to deploy a policy with a ``policy_name`` while the kernel already +has a deployed policy with the same ``policy_name``. + +Deploying a policy will *not* cause IPE to start enforcing the policy. IPE will +only enforce the policy marked active. Note that only one policy can be active +at a time. + +Once deployment is successful, the policy can be activated, by writing file +``/sys/kernel/security/ipe/policies/$policy_name/active``. +For example, the ``Ex_Policy`` can be activated by:: + + echo 1 > "/sys/kernel/security/ipe/policies/Ex_Policy/active" + +From above point on, ``Ex_Policy`` is now the enforced policy on the +system. + +IPE also provides a way to delete policies. This can be done via the +``delete`` securityfs node, +``/sys/kernel/security/ipe/policies/$policy_name/delete``. +Writing ``1`` to that file deletes the policy:: + + echo 1 > "/sys/kernel/security/ipe/policies/$policy_name/delete" + +There is only one requirement to delete a policy: the policy being deleted +must be inactive. + +.. NOTE:: + + If a traditional MAC system is enabled (SELinux, apparmor, smack), all + writes to ipe's securityfs nodes require ``CAP_MAC_ADMIN``. + +Modes +~~~~~ + +IPE supports two modes of operation: permissive (similar to SELinux's +permissive mode) and enforced. In permissive mode, all events are +checked and policy violations are logged, but the policy is not really +enforced. This allows users to test policies before enforcing them. + +The default mode is enforce, and can be changed via the kernel command +line parameter ``ipe.enforce=(0|1)``, or the securityfs node +``/sys/kernel/security/ipe/enforce``. + +.. NOTE:: + + If a traditional MAC system is enabled (SELinux, apparmor, smack, etcetera), + all writes to ipe's securityfs nodes require ``CAP_MAC_ADMIN``. + +Audit Events +~~~~~~~~~~~~ + +1420 AUDIT_IPE_ACCESS +^^^^^^^^^^^^^^^^^^^^^ +Event Examples:: + + type=1420 audit(1653364370.067:61): ipe_op=EXECUTE ipe_hook=MMAP enforcing=1 pid=2241 comm="ld-linux.so" path="/deny/lib/libc.so.6" dev="sda2" ino=14549020 rule="DEFAULT action=DENY" + type=1300 audit(1653364370.067:61): SYSCALL arch=c000003e syscall=9 success=no exit=-13 a0=7f1105a28000 a1=195000 a2=5 a3=812 items=0 ppid=2219 pid=2241 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=pts0 ses=2 comm="ld-linux.so" exe="/tmp/ipe-test/lib/ld-linux.so" subj=unconfined key=(null) + type=1327 audit(1653364370.067:61): 707974686F6E3300746573742F6D61696E2E7079002D6E00 + + type=1420 audit(1653364735.161:64): ipe_op=EXECUTE ipe_hook=MMAP enforcing=1 pid=2472 comm="mmap_test" path=? dev=? ino=? rule="DEFAULT action=DENY" + type=1300 audit(1653364735.161:64): SYSCALL arch=c000003e syscall=9 success=no exit=-13 a0=0 a1=1000 a2=4 a3=21 items=0 ppid=2219 pid=2472 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=pts0 ses=2 comm="mmap_test" exe="/root/overlake_test/upstream_test/vol_fsverity/bin/mmap_test" subj=unconfined key=(null) + type=1327 audit(1653364735.161:64): 707974686F6E3300746573742F6D61696E2E7079002D6E00 + +This event indicates that IPE made an access control decision; the IPE +specific record (1420) is always emitted in conjunction with a +``AUDITSYSCALL`` record. + +Determining whether IPE is in permissive or enforced mode can be derived +from ``success`` property and exit code of the ``AUDITSYSCALL`` record. + + +Field descriptions: + ++-----------+------------+-----------+---------------------------------------------------------------------------------+ +| Field | Value Type | Optional? | Description of Value | ++===========+============+===========+=================================================================================+ +| ipe_op | string | No | The IPE operation name associated with the log | ++-----------+------------+-----------+---------------------------------------------------------------------------------+ +| ipe_hook | string | No | The name of the LSM hook that triggered the IPE event | ++-----------+------------+-----------+---------------------------------------------------------------------------------+ +| enforcing | integer | No | The current IPE enforcing state 1 is in enforcing mode, 0 is in permissive mode | ++-----------+------------+-----------+---------------------------------------------------------------------------------+ +| pid | integer | No | The pid of the process that triggered the IPE event. | ++-----------+------------+-----------+---------------------------------------------------------------------------------+ +| comm | string | No | The command line program name of the process that triggered the IPE event | ++-----------+------------+-----------+---------------------------------------------------------------------------------+ +| path | string | Yes | The absolute path to the evaluated file | ++-----------+------------+-----------+---------------------------------------------------------------------------------+ +| ino | integer | Yes | The inode number of the evaluated file | ++-----------+------------+-----------+---------------------------------------------------------------------------------+ +| dev | string | Yes | The device name of the evaluated file, e.g. vda | ++-----------+------------+-----------+---------------------------------------------------------------------------------+ +| rule | string | No | The matched policy rule | ++-----------+------------+-----------+---------------------------------------------------------------------------------+ + +1421 AUDIT_IPE_CONFIG_CHANGE +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Event Example:: + + type=1421 audit(1653425583.136:54): old_active_pol_name="Allow_All" old_active_pol_version=0.0.0 old_policy_digest=sha256:E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855 new_active_pol_name="boot_verified" new_active_pol_version=0.0.0 new_policy_digest=sha256:820EEA5B40CA42B51F68962354BA083122A20BB846F26765076DD8EED7B8F4DB auid=4294967295 ses=4294967295 lsm=ipe res=1 + type=1300 audit(1653425583.136:54): SYSCALL arch=c000003e syscall=1 success=yes exit=2 a0=3 a1=5596fcae1fb0 a2=2 a3=2 items=0 ppid=184 pid=229 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=pts0 ses=4294967295 comm="python3" exe="/usr/bin/python3.10" key=(null) + type=1327 audit(1653425583.136:54): PROCTITLE proctitle=707974686F6E3300746573742F6D61696E2E7079002D66002E2 + +This event indicates that IPE switched the active poliy from one to another +along with the version and the hash digest of the two policies. +Note IPE can only have one policy active at a time, all access decision +evaluation is based on the current active policy. +The normal procedure to deploy a new policy is loading the policy to deploy +into the kernel first, then switch the active policy to it. + +This record will always be emitted in conjunction with a ``AUDITSYSCALL`` record for the ``write`` syscall. + +Field descriptions: + ++------------------------+------------+-----------+---------------------------------------------------+ +| Field | Value Type | Optional? | Description of Value | ++========================+============+===========+===================================================+ +| old_active_pol_name | string | Yes | The name of previous active policy | ++------------------------+------------+-----------+---------------------------------------------------+ +| old_active_pol_version | string | Yes | The version of previous active policy | ++------------------------+------------+-----------+---------------------------------------------------+ +| old_policy_digest | string | Yes | The hash of previous active policy | ++------------------------+------------+-----------+---------------------------------------------------+ +| new_active_pol_name | string | No | The name of current active policy | ++------------------------+------------+-----------+---------------------------------------------------+ +| new_active_pol_version | string | No | The version of current active policy | ++------------------------+------------+-----------+---------------------------------------------------+ +| new_policy_digest | string | No | The hash of current active policy | ++------------------------+------------+-----------+---------------------------------------------------+ +| auid | integer | No | The login user ID | ++------------------------+------------+-----------+---------------------------------------------------+ +| ses | integer | No | The login session ID | ++------------------------+------------+-----------+---------------------------------------------------+ +| lsm | string | No | The lsm name associated with the event | ++------------------------+------------+-----------+---------------------------------------------------+ +| res | integer | No | The result of the audited operation(success/fail) | ++------------------------+------------+-----------+---------------------------------------------------+ + +1422 AUDIT_IPE_POLICY_LOAD +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Event Example:: + + type=1422 audit(1653425529.927:53): policy_name="boot_verified" policy_version=0.0.0 policy_digest=sha256:820EEA5B40CA42B51F68962354BA083122A20BB846F26765076DD8EED7B8F4DB auid=4294967295 ses=4294967295 lsm=ipe res=1 errno=0 + type=1300 audit(1653425529.927:53): arch=c000003e syscall=1 success=yes exit=2567 a0=3 a1=5596fcae1fb0 a2=a07 a3=2 items=0 ppid=184 pid=229 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=pts0 ses=4294967295 comm="python3" exe="/usr/bin/python3.10" key=(null) + type=1327 audit(1653425529.927:53): PROCTITLE proctitle=707974686F6E3300746573742F6D61696E2E7079002D66002E2E + +This record indicates a new policy has been loaded into the kernel with the policy name, policy version and policy hash. + +This record will always be emitted in conjunction with a ``AUDITSYSCALL`` record for the ``write`` syscall. + +Field descriptions: + ++----------------+------------+-----------+-------------------------------------------------------------+ +| Field | Value Type | Optional? | Description of Value | ++================+============+===========+=============================================================+ +| policy_name | string | Yes | The policy_name | ++----------------+------------+-----------+-------------------------------------------------------------+ +| policy_version | string | Yes | The policy_version | ++----------------+------------+-----------+-------------------------------------------------------------+ +| policy_digest | string | Yes | The policy hash | ++----------------+------------+-----------+-------------------------------------------------------------+ +| auid | integer | No | The login user ID | ++----------------+------------+-----------+-------------------------------------------------------------+ +| ses | integer | No | The login session ID | ++----------------+------------+-----------+-------------------------------------------------------------+ +| lsm | string | No | The lsm name associated with the event | ++----------------+------------+-----------+-------------------------------------------------------------+ +| res | integer | No | The result of the audited operation(success/fail) | ++----------------+------------+-----------+-------------------------------------------------------------+ +| errno | integer | No | Error code from policy loading operations (see table below) | ++----------------+------------+-----------+-------------------------------------------------------------+ + +Policy error codes (errno): + +The following table lists the error codes that may appear in the errno field while loading or updating the policy: + ++----------------+--------------------------------------------------------+ +| Error Code | Description | ++================+========================================================+ +| 0 | Success | ++----------------+--------------------------------------------------------+ +| -EPERM | Insufficient permission | ++----------------+--------------------------------------------------------+ +| -EEXIST | Same name policy already deployed | ++----------------+--------------------------------------------------------+ +| -EBADMSG | Policy is invalid | ++----------------+--------------------------------------------------------+ +| -ENOMEM | Out of memory (OOM) | ++----------------+--------------------------------------------------------+ +| -ERANGE | Policy version number overflow | ++----------------+--------------------------------------------------------+ +| -EINVAL | Policy version parsing error | ++----------------+--------------------------------------------------------+ +| -ENOKEY | Key used to sign the IPE policy not found in keyring | ++----------------+--------------------------------------------------------+ +| -EKEYREJECTED | Policy signature verification failed | ++----------------+--------------------------------------------------------+ +| -ESTALE | Attempting to update an IPE policy with older version | ++----------------+--------------------------------------------------------+ +| -ENOENT | Policy was deleted while updating | ++----------------+--------------------------------------------------------+ + +1404 AUDIT_MAC_STATUS +^^^^^^^^^^^^^^^^^^^^^ + +Event Examples:: + + type=1404 audit(1653425689.008:55): enforcing=0 old_enforcing=1 auid=4294967295 ses=4294967295 enabled=1 old-enabled=1 lsm=ipe res=1 + type=1300 audit(1653425689.008:55): arch=c000003e syscall=1 success=yes exit=2 a0=1 a1=55c1065e5c60 a2=2 a3=0 items=0 ppid=405 pid=441 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=) + type=1327 audit(1653425689.008:55): proctitle="-bash" + + type=1404 audit(1653425689.008:55): enforcing=1 old_enforcing=0 auid=4294967295 ses=4294967295 enabled=1 old-enabled=1 lsm=ipe res=1 + type=1300 audit(1653425689.008:55): arch=c000003e syscall=1 success=yes exit=2 a0=1 a1=55c1065e5c60 a2=2 a3=0 items=0 ppid=405 pid=441 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=) + type=1327 audit(1653425689.008:55): proctitle="-bash" + +This record will always be emitted in conjunction with a ``AUDITSYSCALL`` record for the ``write`` syscall. + +Field descriptions: + ++---------------+------------+-----------+-------------------------------------------------------------------------------------------------+ +| Field | Value Type | Optional? | Description of Value | ++===============+============+===========+=================================================================================================+ +| enforcing | integer | No | The enforcing state IPE is being switched to, 1 is in enforcing mode, 0 is in permissive mode | ++---------------+------------+-----------+-------------------------------------------------------------------------------------------------+ +| old_enforcing | integer | No | The enforcing state IPE is being switched from, 1 is in enforcing mode, 0 is in permissive mode | ++---------------+------------+-----------+-------------------------------------------------------------------------------------------------+ +| auid | integer | No | The login user ID | ++---------------+------------+-----------+-------------------------------------------------------------------------------------------------+ +| ses | integer | No | The login session ID | ++---------------+------------+-----------+-------------------------------------------------------------------------------------------------+ +| enabled | integer | No | The new TTY audit enabled setting | ++---------------+------------+-----------+-------------------------------------------------------------------------------------------------+ +| old-enabled | integer | No | The old TTY audit enabled setting | ++---------------+------------+-----------+-------------------------------------------------------------------------------------------------+ +| lsm | string | No | The lsm name associated with the event | ++---------------+------------+-----------+-------------------------------------------------------------------------------------------------+ +| res | integer | No | The result of the audited operation(success/fail) | ++---------------+------------+-----------+-------------------------------------------------------------------------------------------------+ + + +Success Auditing +^^^^^^^^^^^^^^^^ + +IPE supports success auditing. When enabled, all events that pass IPE +policy and are not blocked will emit an audit event. This is disabled by +default, and can be enabled via the kernel command line +``ipe.success_audit=(0|1)`` or +``/sys/kernel/security/ipe/success_audit`` securityfs file. + +This is *very* noisy, as IPE will check every userspace binary on the +system, but is useful for debugging policies. + +.. NOTE:: + + If a traditional MAC system is enabled (SELinux, apparmor, smack, etcetera), + all writes to ipe's securityfs nodes require ``CAP_MAC_ADMIN``. + +Properties +---------- + +As explained above, IPE properties are ``key=value`` pairs expressed in IPE +policy. Two properties are built-into the policy parser: 'op' and 'action'. +The other properties are used to restrict immutable security properties +about the files being evaluated. Currently those properties are: +'``boot_verified``', '``dmverity_signature``', '``dmverity_roothash``', +'``fsverity_signature``', '``fsverity_digest``'. A description of all +properties supported by IPE are listed below: + +op +~~ + +Indicates the operation for a rule to apply to. Must be in every rule, +as the first token. IPE supports the following operations: + + ``EXECUTE`` + + Pertains to any file attempting to be executed, or loaded as an + executable. + + ``FIRMWARE``: + + Pertains to firmware being loaded via the firmware_class interface. + This covers both the preallocated buffer and the firmware file + itself. + + ``KMODULE``: + + Pertains to loading kernel modules via ``modprobe`` or ``insmod``. + + ``KEXEC_IMAGE``: + + Pertains to kernel images loading via ``kexec``. + + ``KEXEC_INITRAMFS`` + + Pertains to initrd images loading via ``kexec --initrd``. + + ``POLICY``: + + Controls loading policies via reading a kernel-space initiated read. + + An example of such is loading IMA policies by writing the path + to the policy file to ``$securityfs/ima/policy`` + + ``X509_CERT``: + + Controls loading IMA certificates through the Kconfigs, + ``CONFIG_IMA_X509_PATH`` and ``CONFIG_EVM_X509_PATH``. + +action +~~~~~~ + + Determines what IPE should do when a rule matches. Must be in every + rule, as the final clause. Can be one of: + + ``ALLOW``: + + If the rule matches, explicitly allow access to the resource to proceed + without executing any more rules. + + ``DENY``: + + If the rule matches, explicitly prohibit access to the resource to + proceed without executing any more rules. + +boot_verified +~~~~~~~~~~~~~ + + This property can be utilized for authorization of files from initramfs. + The format of this property is:: + + boot_verified=(TRUE|FALSE) + + + .. WARNING:: + + This property will trust files from initramfs(rootfs). It should + only be used during early booting stage. Before mounting the real + rootfs on top of the initramfs, initramfs script will recursively + remove all files and directories on the initramfs. This is typically + implemented by using switch_root(8) [#switch_root]_. Therefore the + initramfs will be empty and not accessible after the real + rootfs takes over. It is advised to switch to a different policy + that doesn't rely on the property after this point. + This ensures that the trust policies remain relevant and effective + throughout the system's operation. + +dmverity_roothash +~~~~~~~~~~~~~~~~~ + + This property can be utilized for authorization or revocation of + specific dm-verity volumes, identified via their root hashes. It has a + dependency on the DM_VERITY module. This property is controlled by + the ``IPE_PROP_DM_VERITY`` config option, it will be automatically + selected when ``SECURITY_IPE`` and ``DM_VERITY`` are all enabled. + The format of this property is:: + + dmverity_roothash=DigestName:HexadecimalString + + The supported DigestNames for dmverity_roothash are [#dmveritydigests]_ + + + blake2b-512 + + blake2s-256 + + sha256 + + sha384 + + sha512 + + sha3-224 + + sha3-256 + + sha3-384 + + sha3-512 + + sm3 + + rmd160 + +dmverity_signature +~~~~~~~~~~~~~~~~~~ + + This property can be utilized for authorization of all dm-verity + volumes that have a signed roothash that validated by a keyring + specified by dm-verity's configuration, either the system trusted + keyring, or the secondary keyring. It depends on + ``DM_VERITY_VERIFY_ROOTHASH_SIG`` config option and is controlled by + the ``IPE_PROP_DM_VERITY_SIGNATURE`` config option, it will be automatically + selected when ``SECURITY_IPE``, ``DM_VERITY`` and + ``DM_VERITY_VERIFY_ROOTHASH_SIG`` are all enabled. + The format of this property is:: + + dmverity_signature=(TRUE|FALSE) + +fsverity_digest +~~~~~~~~~~~~~~~ + + This property can be utilized for authorization of specific fsverity + enabled files, identified via their fsverity digests. + It depends on ``FS_VERITY`` config option and is controlled by + the ``IPE_PROP_FS_VERITY`` config option, it will be automatically + selected when ``SECURITY_IPE`` and ``FS_VERITY`` are all enabled. + The format of this property is:: + + fsverity_digest=DigestName:HexadecimalString + + The supported DigestNames for fsverity_digest are [#fsveritydigest]_ + + + sha256 + + sha512 + +fsverity_signature +~~~~~~~~~~~~~~~~~~ + + This property is used to authorize all fs-verity enabled files that have + been verified by fs-verity's built-in signature mechanism. The signature + verification relies on a key stored within the ".fs-verity" keyring. It + depends on ``FS_VERITY_BUILTIN_SIGNATURES`` config option and + it is controlled by the ``IPE_PROP_FS_VERITY`` config option, + it will be automatically selected when ``SECURITY_IPE``, ``FS_VERITY`` + and ``FS_VERITY_BUILTIN_SIGNATURES`` are all enabled. + The format of this property is:: + + fsverity_signature=(TRUE|FALSE) + +Policy Examples +--------------- + +Allow all +~~~~~~~~~ + +:: + + policy_name=Allow_All policy_version=0.0.0 + DEFAULT action=ALLOW + +Allow only initramfs +~~~~~~~~~~~~~~~~~~~~ + +:: + + policy_name=Allow_Initramfs policy_version=0.0.0 + DEFAULT action=DENY + + op=EXECUTE boot_verified=TRUE action=ALLOW + +Allow any signed and validated dm-verity volume and the initramfs +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + policy_name=Allow_Signed_DMV_And_Initramfs policy_version=0.0.0 + DEFAULT action=DENY + + op=EXECUTE boot_verified=TRUE action=ALLOW + op=EXECUTE dmverity_signature=TRUE action=ALLOW + +Prohibit execution from a specific dm-verity volume +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + policy_name=Deny_DMV_By_Roothash policy_version=0.0.0 + DEFAULT action=DENY + + op=EXECUTE dmverity_roothash=sha256:cd2c5bae7c6c579edaae4353049d58eb5f2e8be0244bf05345bc8e5ed257baff action=DENY + + op=EXECUTE boot_verified=TRUE action=ALLOW + op=EXECUTE dmverity_signature=TRUE action=ALLOW + +Allow only a specific dm-verity volume +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + policy_name=Allow_DMV_By_Roothash policy_version=0.0.0 + DEFAULT action=DENY + + op=EXECUTE dmverity_roothash=sha256:401fcec5944823ae12f62726e8184407a5fa9599783f030dec146938 action=ALLOW + +Allow any fs-verity file with a valid built-in signature +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + policy_name=Allow_Signed_And_Validated_FSVerity policy_version=0.0.0 + DEFAULT action=DENY + + op=EXECUTE fsverity_signature=TRUE action=ALLOW + +Allow execution of a specific fs-verity file +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + policy_name=ALLOW_FSV_By_Digest policy_version=0.0.0 + DEFAULT action=DENY + + op=EXECUTE fsverity_digest=sha256:fd88f2b8824e197f850bf4c5109bea5cf0ee38104f710843bb72da796ba5af9e action=ALLOW + +Additional Information +---------------------- + +- `Github Repository <https://github.com/microsoft/ipe>`_ +- :doc:`Developer and design docs for IPE </security/ipe>` + +FAQ +--- + +Q: + What's the difference between other LSMs which provide a measure of + trust-based access control? + +A: + + In general, there's two other LSMs that can provide similar functionality: + IMA, and Loadpin. + + IMA and IPE are functionally very similar. The significant difference between + the two is the policy. [#devdoc]_ + + Loadpin and IPE differ fairly dramatically, as Loadpin only covers the IPE's + kernel read operations, whereas IPE is capable of controlling execution + on top of kernel read. The trust model is also different; Loadpin roots its + trust in the initial super-block, whereas trust in IPE is stemmed from kernel + itself (via ``SYSTEM_TRUSTED_KEYS``). + +----------- + +.. [#digest_cache_lsm] https://lore.kernel.org/lkml/20240415142436.2545003-1-roberto.sassu@huaweicloud.com/ + +.. [#interpreters] There is `some interest in solving this issue <https://lore.kernel.org/lkml/20220321161557.495388-1-mic@digikod.net/>`_. + +.. [#devdoc] Please see :doc:`the design docs </security/ipe>` for more on + this topic. + +.. [#switch_root] https://man7.org/linux/man-pages/man8/switch_root.8.html + +.. [#dmveritydigests] These hash algorithms are based on values accepted by + the Linux crypto API; IPE does not impose any + restrictions on the digest algorithm itself; + thus, this list may be out of date. + +.. [#fsveritydigest] These hash algorithms are based on values accepted by the + kernel's fsverity support; IPE does not impose any + restrictions on the digest algorithm itself; + thus, this list may be out of date. diff --git a/Documentation/admin-guide/LSM/landlock.rst b/Documentation/admin-guide/LSM/landlock.rst new file mode 100644 index 000000000000..9e61607def08 --- /dev/null +++ b/Documentation/admin-guide/LSM/landlock.rst @@ -0,0 +1,158 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. Copyright © 2025 Microsoft Corporation + +================================ +Landlock: system-wide management +================================ + +:Author: Mickaël Salaün +:Date: March 2025 + +Landlock can leverage the audit framework to log events. + +User space documentation can be found here: +Documentation/userspace-api/landlock.rst. + +Audit +===== + +Denied access requests are logged by default for a sandboxed program if `audit` +is enabled. This default behavior can be changed with the +sys_landlock_restrict_self() flags (cf. +Documentation/userspace-api/landlock.rst). Landlock logs can also be masked +thanks to audit rules. Landlock can generate 2 audit record types. + +Record types +------------ + +AUDIT_LANDLOCK_ACCESS + This record type identifies a denied access request to a kernel resource. + The ``domain`` field indicates the ID of the domain that blocked the + request. The ``blockers`` field indicates the cause(s) of this denial + (separated by a comma), and the following fields identify the kernel object + (similar to SELinux). There may be more than one of this record type per + audit event. + + Example with a file link request generating two records in the same event:: + + domain=195ba459b blockers=fs.refer path="/usr/bin" dev="vda2" ino=351 + domain=195ba459b blockers=fs.make_reg,fs.refer path="/usr/local" dev="vda2" ino=365 + +AUDIT_LANDLOCK_DOMAIN + This record type describes the status of a Landlock domain. The ``status`` + field can be either ``allocated`` or ``deallocated``. + + The ``allocated`` status is part of the same audit event and follows + the first logged ``AUDIT_LANDLOCK_ACCESS`` record of a domain. It identifies + Landlock domain information at the time of the sys_landlock_restrict_self() + call with the following fields: + + - the ``domain`` ID + - the enforcement ``mode`` + - the domain creator's ``pid`` + - the domain creator's ``uid`` + - the domain creator's executable path (``exe``) + - the domain creator's command line (``comm``) + + Example:: + + domain=195ba459b status=allocated mode=enforcing pid=300 uid=0 exe="/root/sandboxer" comm="sandboxer" + + The ``deallocated`` status is an event on its own and it identifies a + Landlock domain release. After such event, it is guarantee that the + related domain ID will never be reused during the lifetime of the system. + The ``domain`` field indicates the ID of the domain which is released, and + the ``denials`` field indicates the total number of denied access request, + which might not have been logged according to the audit rules and + sys_landlock_restrict_self()'s flags. + + Example:: + + domain=195ba459b status=deallocated denials=3 + + +Event samples +-------------- + +Here are two examples of log events (see serial numbers). + +In this example a sandboxed program (``kill``) tries to send a signal to the +init process, which is denied because of the signal scoping restriction +(``LL_SCOPED=s``):: + + $ LL_FS_RO=/ LL_FS_RW=/ LL_SCOPED=s LL_FORCE_LOG=1 ./sandboxer kill 1 + +This command generates two events, each identified with a unique serial +number following a timestamp (``msg=audit(1729738800.268:30)``). The first +event (serial ``30``) contains 4 records. The first record +(``type=LANDLOCK_ACCESS``) shows an access denied by the domain `1a6fdc66f`. +The cause of this denial is signal scopping restriction +(``blockers=scope.signal``). The process that would have receive this signal +is the init process (``opid=1 ocomm="systemd"``). + +The second record (``type=LANDLOCK_DOMAIN``) describes (``status=allocated``) +domain `1a6fdc66f`. This domain was created by process ``286`` executing the +``/root/sandboxer`` program launched by the root user. + +The third record (``type=SYSCALL``) describes the syscall, its provided +arguments, its result (``success=no exit=-1``), and the process that called it. + +The fourth record (``type=PROCTITLE``) shows the command's name as an +hexadecimal value. This can be translated with ``python -c +'print(bytes.fromhex("6B696C6C0031"))'``. + +Finally, the last record (``type=LANDLOCK_DOMAIN``) is also the only one from +the second event (serial ``31``). It is not tied to a direct user space action +but an asynchronous one to free resources tied to a Landlock domain +(``status=deallocated``). This can be useful to know that the following logs +will not concern the domain ``1a6fdc66f`` anymore. This record also summarize +the number of requests this domain denied (``denials=1``), whether they were +logged or not. + +.. code-block:: + + type=LANDLOCK_ACCESS msg=audit(1729738800.268:30): domain=1a6fdc66f blockers=scope.signal opid=1 ocomm="systemd" + type=LANDLOCK_DOMAIN msg=audit(1729738800.268:30): domain=1a6fdc66f status=allocated mode=enforcing pid=286 uid=0 exe="/root/sandboxer" comm="sandboxer" + type=SYSCALL msg=audit(1729738800.268:30): arch=c000003e syscall=62 success=no exit=-1 [..] ppid=272 pid=286 auid=0 uid=0 gid=0 [...] comm="kill" [...] + type=PROCTITLE msg=audit(1729738800.268:30): proctitle=6B696C6C0031 + type=LANDLOCK_DOMAIN msg=audit(1729738800.324:31): domain=1a6fdc66f status=deallocated denials=1 + +Here is another example showcasing filesystem access control:: + + $ LL_FS_RO=/ LL_FS_RW=/tmp LL_FORCE_LOG=1 ./sandboxer sh -c "echo > /etc/passwd" + +The related audit logs contains 8 records from 3 different events (serials 33, +34 and 35) created by the same domain `1a6fdc679`:: + + type=LANDLOCK_ACCESS msg=audit(1729738800.221:33): domain=1a6fdc679 blockers=fs.write_file path="/dev/tty" dev="devtmpfs" ino=9 + type=LANDLOCK_DOMAIN msg=audit(1729738800.221:33): domain=1a6fdc679 status=allocated mode=enforcing pid=289 uid=0 exe="/root/sandboxer" comm="sandboxer" + type=SYSCALL msg=audit(1729738800.221:33): arch=c000003e syscall=257 success=no exit=-13 [...] ppid=272 pid=289 auid=0 uid=0 gid=0 [...] comm="sh" [...] + type=PROCTITLE msg=audit(1729738800.221:33): proctitle=7368002D63006563686F203E202F6574632F706173737764 + type=LANDLOCK_ACCESS msg=audit(1729738800.221:34): domain=1a6fdc679 blockers=fs.write_file path="/etc/passwd" dev="vda2" ino=143821 + type=SYSCALL msg=audit(1729738800.221:34): arch=c000003e syscall=257 success=no exit=-13 [...] ppid=272 pid=289 auid=0 uid=0 gid=0 [...] comm="sh" [...] + type=PROCTITLE msg=audit(1729738800.221:34): proctitle=7368002D63006563686F203E202F6574632F706173737764 + type=LANDLOCK_DOMAIN msg=audit(1729738800.261:35): domain=1a6fdc679 status=deallocated denials=2 + + +Event filtering +--------------- + +If you get spammed with audit logs related to Landlock, this is either an +attack attempt or a bug in the security policy. We can put in place some +filters to limit noise with two complementary ways: + +- with sys_landlock_restrict_self()'s flags if we can fix the sandboxed + programs, +- or with audit rules (see :manpage:`auditctl(8)`). + +Additional documentation +======================== + +* `Linux Audit Documentation`_ +* Documentation/userspace-api/landlock.rst +* Documentation/security/landlock.rst +* https://landlock.io + +.. Links +.. _Linux Audit Documentation: + https://github.com/linux-audit/audit-documentation/wiki diff --git a/Documentation/admin-guide/LSM/tomoyo.rst b/Documentation/admin-guide/LSM/tomoyo.rst index 4bc9c2b4da6f..bdb2c2e2a1b2 100644 --- a/Documentation/admin-guide/LSM/tomoyo.rst +++ b/Documentation/admin-guide/LSM/tomoyo.rst @@ -9,8 +9,8 @@ TOMOYO is a name-based MAC extension (LSM module) for the Linux kernel. LiveCD-based tutorials are available at -http://tomoyo.sourceforge.jp/1.8/ubuntu12.04-live.html -http://tomoyo.sourceforge.jp/1.8/centos6-live.html +https://tomoyo.sourceforge.net/1.8/ubuntu12.04-live.html +https://tomoyo.sourceforge.net/1.8/centos6-live.html Though these tutorials use non-LSM version of TOMOYO, they are useful for you to know what TOMOYO is. @@ -21,45 +21,32 @@ How to enable TOMOYO? Build the kernel with ``CONFIG_SECURITY_TOMOYO=y`` and pass ``security=tomoyo`` on kernel's command line. -Please see http://tomoyo.osdn.jp/2.5/ for details. +Please see https://tomoyo.sourceforge.net/2.6/ for details. Where is documentation? ======================= User <-> Kernel interface documentation is available at -https://tomoyo.osdn.jp/2.5/policy-specification/index.html . +https://tomoyo.sourceforge.net/2.6/policy-specification/index.html . Materials we prepared for seminars and symposiums are available at -https://osdn.jp/projects/tomoyo/docs/?category_id=532&language_id=1 . +https://sourceforge.net/projects/tomoyo/files/docs/ . Below lists are chosen from three aspects. What is TOMOYO? TOMOYO Linux Overview - https://osdn.jp/projects/tomoyo/docs/lca2009-takeda.pdf + https://sourceforge.net/projects/tomoyo/files/docs/lca2009-takeda.pdf TOMOYO Linux: pragmatic and manageable security for Linux - https://osdn.jp/projects/tomoyo/docs/freedomhectaipei-tomoyo.pdf + https://sourceforge.net/projects/tomoyo/files/docs/freedomhectaipei-tomoyo.pdf TOMOYO Linux: A Practical Method to Understand and Protect Your Own Linux Box - https://osdn.jp/projects/tomoyo/docs/PacSec2007-en-no-demo.pdf + https://sourceforge.net/projects/tomoyo/files/docs/PacSec2007-en-no-demo.pdf What can TOMOYO do? Deep inside TOMOYO Linux - https://osdn.jp/projects/tomoyo/docs/lca2009-kumaneko.pdf + https://sourceforge.net/projects/tomoyo/files/docs/lca2009-kumaneko.pdf The role of "pathname based access control" in security. - https://osdn.jp/projects/tomoyo/docs/lfj2008-bof.pdf + https://sourceforge.net/projects/tomoyo/files/docs/lfj2008-bof.pdf History of TOMOYO? Realities of Mainlining - https://osdn.jp/projects/tomoyo/docs/lfj2008.pdf - -What is future plan? -==================== - -We believe that inode based security and name based security are complementary -and both should be used together. But unfortunately, so far, we cannot enable -multiple LSM modules at the same time. We feel sorry that you have to give up -SELinux/SMACK/AppArmor etc. when you want to use TOMOYO. - -We hope that LSM becomes stackable in future. Meanwhile, you can use non-LSM -version of TOMOYO, available at http://tomoyo.osdn.jp/1.8/ . -LSM version of TOMOYO is a subset of non-LSM version of TOMOYO. We are planning -to port non-LSM version's functionalities to LSM versions. + https://sourceforge.net/projects/tomoyo/files/docs/lfj2008.pdf |