606 lines
29 KiB
Plaintext
606 lines
29 KiB
Plaintext
======================
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(Un)patching Callbacks
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======================
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Livepatch (un)patch-callbacks provide a mechanism for livepatch modules
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to execute callback functions when a kernel object is (un)patched. They
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can be considered a "power feature" that extends livepatching abilities
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to include:
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- Safe updates to global data
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- "Patches" to init and probe functions
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- Patching otherwise unpatchable code (i.e. assembly)
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In most cases, (un)patch callbacks will need to be used in conjunction
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with memory barriers and kernel synchronization primitives, like
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mutexes/spinlocks, or even stop_machine(), to avoid concurrency issues.
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Callbacks differ from existing kernel facilities:
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- Module init/exit code doesn't run when disabling and re-enabling a
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patch.
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- A module notifier can't stop a to-be-patched module from loading.
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Callbacks are part of the klp_object structure and their implementation
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is specific to that klp_object. Other livepatch objects may or may not
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be patched, irrespective of the target klp_object's current state.
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Callbacks can be registered for the following livepatch actions:
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* Pre-patch - before a klp_object is patched
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* Post-patch - after a klp_object has been patched and is active
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across all tasks
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* Pre-unpatch - before a klp_object is unpatched (ie, patched code is
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active), used to clean up post-patch callback
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resources
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* Post-unpatch - after a klp_object has been patched, all code has
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been restored and no tasks are running patched code,
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used to cleanup pre-patch callback resources
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Each callback is optional, omitting one does not preclude specifying any
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other. However, the livepatching core executes the handlers in
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symmetry: pre-patch callbacks have a post-unpatch counterpart and
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post-patch callbacks have a pre-unpatch counterpart. An unpatch
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callback will only be executed if its corresponding patch callback was
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executed. Typical use cases pair a patch handler that acquires and
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configures resources with an unpatch handler tears down and releases
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those same resources.
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A callback is only executed if its host klp_object is loaded. For
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in-kernel vmlinux targets, this means that callbacks will always execute
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when a livepatch is enabled/disabled. For patch target kernel modules,
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callbacks will only execute if the target module is loaded. When a
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module target is (un)loaded, its callbacks will execute only if the
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livepatch module is enabled.
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The pre-patch callback, if specified, is expected to return a status
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code (0 for success, -ERRNO on error). An error status code indicates
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to the livepatching core that patching of the current klp_object is not
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safe and to stop the current patching request. (When no pre-patch
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callback is provided, the transition is assumed to be safe.) If a
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pre-patch callback returns failure, the kernel's module loader will:
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- Refuse to load a livepatch, if the livepatch is loaded after
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targeted code.
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or:
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- Refuse to load a module, if the livepatch was already successfully
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loaded.
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No post-patch, pre-unpatch, or post-unpatch callbacks will be executed
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for a given klp_object if the object failed to patch, due to a failed
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pre_patch callback or for any other reason.
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If a patch transition is reversed, no pre-unpatch handlers will be run
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(this follows the previously mentioned symmetry -- pre-unpatch callbacks
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will only occur if their corresponding post-patch callback executed).
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If the object did successfully patch, but the patch transition never
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started for some reason (e.g., if another object failed to patch),
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only the post-unpatch callback will be called.
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Example Use-cases
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=================
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Update global data
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------------------
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A pre-patch callback can be useful to update a global variable. For
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example, 75ff39ccc1bd ("tcp: make challenge acks less predictable")
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changes a global sysctl, as well as patches the tcp_send_challenge_ack()
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function.
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In this case, if we're being super paranoid, it might make sense to
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patch the data *after* patching is complete with a post-patch callback,
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so that tcp_send_challenge_ack() could first be changed to read
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sysctl_tcp_challenge_ack_limit with READ_ONCE.
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Support __init and probe function patches
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-----------------------------------------
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Although __init and probe functions are not directly livepatch-able, it
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may be possible to implement similar updates via pre/post-patch
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callbacks.
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48900cb6af42 ("virtio-net: drop NETIF_F_FRAGLIST") change the way that
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virtnet_probe() initialized its driver's net_device features. A
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pre/post-patch callback could iterate over all such devices, making a
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similar change to their hw_features value. (Client functions of the
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value may need to be updated accordingly.)
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Test cases
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==========
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What follows is not an exhaustive test suite of every possible livepatch
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pre/post-(un)patch combination, but a selection that demonstrates a few
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important concepts. Each test case uses the kernel modules located in
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the samples/livepatch/ and assumes that no livepatches are loaded at the
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beginning of the test.
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Test 1
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------
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Test a combination of loading a kernel module and a livepatch that
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patches a function in the first module. (Un)load the target module
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before the livepatch module:
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- load target module
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- load livepatch
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- disable livepatch
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- unload target module
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- unload livepatch
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First load a target module:
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% insmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 34.475708] livepatch_callbacks_mod: livepatch_callbacks_mod_init
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On livepatch enable, before the livepatch transition starts, pre-patch
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callbacks are executed for vmlinux and livepatch_callbacks_mod (those
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klp_objects currently loaded). After klp_objects are patched according
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to the klp_patch, their post-patch callbacks run and the transition
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completes:
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% insmod samples/livepatch/livepatch-callbacks-demo.ko
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[ 36.503719] livepatch: enabling patch 'livepatch_callbacks_demo'
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[ 36.504213] livepatch: 'livepatch_callbacks_demo': initializing patching transition
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[ 36.504238] livepatch_callbacks_demo: pre_patch_callback: vmlinux
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[ 36.504721] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
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[ 36.505849] livepatch: 'livepatch_callbacks_demo': starting patching transition
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[ 37.727133] livepatch: 'livepatch_callbacks_demo': completing patching transition
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[ 37.727232] livepatch_callbacks_demo: post_patch_callback: vmlinux
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[ 37.727860] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
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[ 37.728792] livepatch: 'livepatch_callbacks_demo': patching complete
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Similarly, on livepatch disable, pre-patch callbacks run before the
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unpatching transition starts. klp_objects are reverted, post-patch
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callbacks execute and the transition completes:
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% echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
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[ 38.510209] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
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[ 38.510234] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
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[ 38.510982] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
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[ 38.512209] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
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[ 39.711132] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
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[ 39.711210] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
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[ 39.711779] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
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[ 39.712735] livepatch: 'livepatch_callbacks_demo': unpatching complete
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% rmmod samples/livepatch/livepatch-callbacks-demo.ko
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% rmmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 42.534183] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
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Test 2
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------
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This test is similar to the previous test, but (un)load the livepatch
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module before the target kernel module. This tests the livepatch core's
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module_coming handler:
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- load livepatch
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- load target module
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- disable livepatch
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- unload livepatch
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- unload target module
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On livepatch enable, only pre/post-patch callbacks are executed for
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currently loaded klp_objects, in this case, vmlinux:
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% insmod samples/livepatch/livepatch-callbacks-demo.ko
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[ 44.553328] livepatch: enabling patch 'livepatch_callbacks_demo'
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[ 44.553997] livepatch: 'livepatch_callbacks_demo': initializing patching transition
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[ 44.554049] livepatch_callbacks_demo: pre_patch_callback: vmlinux
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[ 44.554845] livepatch: 'livepatch_callbacks_demo': starting patching transition
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[ 45.727128] livepatch: 'livepatch_callbacks_demo': completing patching transition
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[ 45.727212] livepatch_callbacks_demo: post_patch_callback: vmlinux
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[ 45.727961] livepatch: 'livepatch_callbacks_demo': patching complete
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When a targeted module is subsequently loaded, only its pre/post-patch
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callbacks are executed:
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% insmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 46.560845] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod'
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[ 46.561988] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
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[ 46.563452] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
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[ 46.565495] livepatch_callbacks_mod: livepatch_callbacks_mod_init
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On livepatch disable, all currently loaded klp_objects' (vmlinux and
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livepatch_callbacks_mod) pre/post-unpatch callbacks are executed:
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% echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
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[ 48.568885] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
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[ 48.568910] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
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[ 48.569441] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
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[ 48.570502] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
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[ 49.759091] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
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[ 49.759171] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
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[ 49.759742] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
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[ 49.760690] livepatch: 'livepatch_callbacks_demo': unpatching complete
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% rmmod samples/livepatch/livepatch-callbacks-demo.ko
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% rmmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 52.592283] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
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Test 3
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------
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Test loading the livepatch after a targeted kernel module, then unload
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the kernel module before disabling the livepatch. This tests the
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livepatch core's module_going handler:
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- load target module
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- load livepatch
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- unload target module
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- disable livepatch
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- unload livepatch
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First load a target module, then the livepatch:
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% insmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 54.607948] livepatch_callbacks_mod: livepatch_callbacks_mod_init
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% insmod samples/livepatch/livepatch-callbacks-demo.ko
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[ 56.613919] livepatch: enabling patch 'livepatch_callbacks_demo'
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[ 56.614411] livepatch: 'livepatch_callbacks_demo': initializing patching transition
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[ 56.614436] livepatch_callbacks_demo: pre_patch_callback: vmlinux
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[ 56.614818] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
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[ 56.615656] livepatch: 'livepatch_callbacks_demo': starting patching transition
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[ 57.759070] livepatch: 'livepatch_callbacks_demo': completing patching transition
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[ 57.759147] livepatch_callbacks_demo: post_patch_callback: vmlinux
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[ 57.759621] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
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[ 57.760307] livepatch: 'livepatch_callbacks_demo': patching complete
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When a target module is unloaded, the livepatch is only reverted from
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that klp_object (livepatch_callbacks_mod). As such, only its pre and
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post-unpatch callbacks are executed when this occurs:
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% rmmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 58.623409] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
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[ 58.623903] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
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[ 58.624658] livepatch: reverting patch 'livepatch_callbacks_demo' on unloading module 'livepatch_callbacks_mod'
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[ 58.625305] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
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When the livepatch is disabled, pre and post-unpatch callbacks are run
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for the remaining klp_object, vmlinux:
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% echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
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[ 60.638420] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
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[ 60.638444] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
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[ 60.638996] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
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[ 61.727088] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
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[ 61.727165] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
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[ 61.727985] livepatch: 'livepatch_callbacks_demo': unpatching complete
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% rmmod samples/livepatch/livepatch-callbacks-demo.ko
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Test 4
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------
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This test is similar to the previous test, however the livepatch is
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loaded first. This tests the livepatch core's module_coming and
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module_going handlers:
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- load livepatch
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- load target module
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- unload target module
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- disable livepatch
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- unload livepatch
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First load the livepatch:
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% insmod samples/livepatch/livepatch-callbacks-demo.ko
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[ 64.661552] livepatch: enabling patch 'livepatch_callbacks_demo'
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[ 64.662147] livepatch: 'livepatch_callbacks_demo': initializing patching transition
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[ 64.662175] livepatch_callbacks_demo: pre_patch_callback: vmlinux
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[ 64.662850] livepatch: 'livepatch_callbacks_demo': starting patching transition
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[ 65.695056] livepatch: 'livepatch_callbacks_demo': completing patching transition
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[ 65.695147] livepatch_callbacks_demo: post_patch_callback: vmlinux
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[ 65.695561] livepatch: 'livepatch_callbacks_demo': patching complete
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When a targeted kernel module is subsequently loaded, only its
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pre/post-patch callbacks are executed:
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% insmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 66.669196] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod'
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[ 66.669882] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
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[ 66.670744] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
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[ 66.672873] livepatch_callbacks_mod: livepatch_callbacks_mod_init
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When the target module is unloaded, the livepatch is only reverted from
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the livepatch_callbacks_mod klp_object. As such, only pre and
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post-unpatch callbacks are executed when this occurs:
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% rmmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 68.680065] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
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[ 68.680688] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
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[ 68.681452] livepatch: reverting patch 'livepatch_callbacks_demo' on unloading module 'livepatch_callbacks_mod'
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[ 68.682094] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
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% echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
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[ 70.689225] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
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[ 70.689256] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
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[ 70.689882] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
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[ 71.711080] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
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[ 71.711481] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
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[ 71.711988] livepatch: 'livepatch_callbacks_demo': unpatching complete
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% rmmod samples/livepatch/livepatch-callbacks-demo.ko
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Test 5
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------
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A simple test of loading a livepatch without one of its patch target
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klp_objects ever loaded (livepatch_callbacks_mod):
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- load livepatch
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- disable livepatch
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- unload livepatch
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Load the livepatch:
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% insmod samples/livepatch/livepatch-callbacks-demo.ko
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[ 74.711081] livepatch: enabling patch 'livepatch_callbacks_demo'
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[ 74.711595] livepatch: 'livepatch_callbacks_demo': initializing patching transition
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[ 74.711639] livepatch_callbacks_demo: pre_patch_callback: vmlinux
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[ 74.712272] livepatch: 'livepatch_callbacks_demo': starting patching transition
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[ 75.743137] livepatch: 'livepatch_callbacks_demo': completing patching transition
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[ 75.743219] livepatch_callbacks_demo: post_patch_callback: vmlinux
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[ 75.743867] livepatch: 'livepatch_callbacks_demo': patching complete
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As expected, only pre/post-(un)patch handlers are executed for vmlinux:
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% echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
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[ 76.716254] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
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[ 76.716278] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
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[ 76.716666] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
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[ 77.727089] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
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[ 77.727194] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
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[ 77.727907] livepatch: 'livepatch_callbacks_demo': unpatching complete
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% rmmod samples/livepatch/livepatch-callbacks-demo.ko
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Test 6
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------
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Test a scenario where a vmlinux pre-patch callback returns a non-zero
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status (ie, failure):
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- load target module
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- load livepatch -ENODEV
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- unload target module
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First load a target module:
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% insmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 80.740520] livepatch_callbacks_mod: livepatch_callbacks_mod_init
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Load the livepatch module, setting its 'pre_patch_ret' value to -19
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(-ENODEV). When its vmlinux pre-patch callback executed, this status
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code will propagate back to the module-loading subsystem. The result is
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that the insmod command refuses to load the livepatch module:
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% insmod samples/livepatch/livepatch-callbacks-demo.ko pre_patch_ret=-19
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[ 82.747326] livepatch: enabling patch 'livepatch_callbacks_demo'
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[ 82.747743] livepatch: 'livepatch_callbacks_demo': initializing patching transition
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[ 82.747767] livepatch_callbacks_demo: pre_patch_callback: vmlinux
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[ 82.748237] livepatch: pre-patch callback failed for object 'vmlinux'
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[ 82.748637] livepatch: failed to enable patch 'livepatch_callbacks_demo'
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[ 82.749059] livepatch: 'livepatch_callbacks_demo': canceling transition, going to unpatch
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[ 82.749060] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
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[ 82.749868] livepatch: 'livepatch_callbacks_demo': unpatching complete
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[ 82.765809] insmod: ERROR: could not insert module samples/livepatch/livepatch-callbacks-demo.ko: No such device
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% rmmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 84.774238] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
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Test 7
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------
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Similar to the previous test, setup a livepatch such that its vmlinux
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pre-patch callback returns success. However, when a targeted kernel
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module is later loaded, have the livepatch return a failing status code:
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- load livepatch
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- setup -ENODEV
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- load target module
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- disable livepatch
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- unload livepatch
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Load the livepatch, notice vmlinux pre-patch callback succeeds:
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% insmod samples/livepatch/livepatch-callbacks-demo.ko
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[ 86.787845] livepatch: enabling patch 'livepatch_callbacks_demo'
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[ 86.788325] livepatch: 'livepatch_callbacks_demo': initializing patching transition
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[ 86.788427] livepatch_callbacks_demo: pre_patch_callback: vmlinux
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[ 86.788821] livepatch: 'livepatch_callbacks_demo': starting patching transition
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[ 87.711069] livepatch: 'livepatch_callbacks_demo': completing patching transition
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[ 87.711143] livepatch_callbacks_demo: post_patch_callback: vmlinux
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[ 87.711886] livepatch: 'livepatch_callbacks_demo': patching complete
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Set a trap so subsequent pre-patch callbacks to this livepatch will
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return -ENODEV:
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% echo -19 > /sys/module/livepatch_callbacks_demo/parameters/pre_patch_ret
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The livepatch pre-patch callback for subsequently loaded target modules
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will return failure, so the module loader refuses to load the kernel
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module. Notice that no post-patch or pre/post-unpatch callbacks are
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executed for this klp_object:
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% insmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 90.796976] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod'
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[ 90.797834] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
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[ 90.798900] livepatch: pre-patch callback failed for object 'livepatch_callbacks_mod'
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[ 90.799652] livepatch: patch 'livepatch_callbacks_demo' failed for module 'livepatch_callbacks_mod', refusing to load module 'livepatch_callbacks_mod'
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[ 90.819737] insmod: ERROR: could not insert module samples/livepatch/livepatch-callbacks-mod.ko: No such device
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However, pre/post-unpatch callbacks run for the vmlinux klp_object:
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% echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
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[ 92.823547] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
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[ 92.823573] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
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[ 92.824331] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
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[ 93.727128] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
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[ 93.727327] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
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[ 93.727861] livepatch: 'livepatch_callbacks_demo': unpatching complete
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% rmmod samples/livepatch/livepatch-callbacks-demo.ko
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Test 8
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------
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Test loading multiple targeted kernel modules. This test-case is
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mainly for comparing with the next test-case.
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- load busy target module (0s sleep),
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- load livepatch
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- load target module
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- unload target module
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- disable livepatch
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- unload livepatch
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- unload busy target module
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Load a target "busy" kernel module which kicks off a worker function
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that immediately exits:
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% insmod samples/livepatch/livepatch-callbacks-busymod.ko sleep_secs=0
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[ 96.910107] livepatch_callbacks_busymod: livepatch_callbacks_mod_init
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[ 96.910600] livepatch_callbacks_busymod: busymod_work_func, sleeping 0 seconds ...
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[ 96.913024] livepatch_callbacks_busymod: busymod_work_func exit
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Proceed with loading the livepatch and another ordinary target module,
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notice that the post-patch callbacks are executed and the transition
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completes quickly:
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% insmod samples/livepatch/livepatch-callbacks-demo.ko
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[ 98.917892] livepatch: enabling patch 'livepatch_callbacks_demo'
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[ 98.918426] livepatch: 'livepatch_callbacks_demo': initializing patching transition
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[ 98.918453] livepatch_callbacks_demo: pre_patch_callback: vmlinux
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[ 98.918955] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state
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[ 98.923835] livepatch: 'livepatch_callbacks_demo': starting patching transition
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[ 99.743104] livepatch: 'livepatch_callbacks_demo': completing patching transition
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[ 99.743156] livepatch_callbacks_demo: post_patch_callback: vmlinux
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[ 99.743679] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state
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[ 99.744616] livepatch: 'livepatch_callbacks_demo': patching complete
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% insmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 100.930955] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod'
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[ 100.931668] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
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[ 100.932645] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
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[ 100.934125] livepatch_callbacks_mod: livepatch_callbacks_mod_init
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% rmmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 102.942805] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
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[ 102.943640] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
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[ 102.944585] livepatch: reverting patch 'livepatch_callbacks_demo' on unloading module 'livepatch_callbacks_mod'
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[ 102.945455] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
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% echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
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[ 104.953815] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
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[ 104.953838] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
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[ 104.954431] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state
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[ 104.955426] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
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[ 106.719073] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
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[ 106.722633] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
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[ 106.723282] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state
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[ 106.724279] livepatch: 'livepatch_callbacks_demo': unpatching complete
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% rmmod samples/livepatch/livepatch-callbacks-demo.ko
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% rmmod samples/livepatch/livepatch-callbacks-busymod.ko
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[ 108.975660] livepatch_callbacks_busymod: livepatch_callbacks_mod_exit
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Test 9
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------
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A similar test as the previous one, but force the "busy" kernel module
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to do longer work.
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The livepatching core will refuse to patch a task that is currently
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executing a to-be-patched function -- the consistency model stalls the
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current patch transition until this safety-check is met. Test a
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scenario where one of a livepatch's target klp_objects sits on such a
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function for a long time. Meanwhile, load and unload other target
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kernel modules while the livepatch transition is in progress.
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- load busy target module (30s sleep)
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- load livepatch
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- load target module
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- unload target module
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- disable livepatch
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- unload livepatch
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- unload busy target module
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Load the "busy" kernel module, this time make it do 30 seconds worth of
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work:
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% insmod samples/livepatch/livepatch-callbacks-busymod.ko sleep_secs=30
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[ 110.993362] livepatch_callbacks_busymod: livepatch_callbacks_mod_init
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[ 110.994059] livepatch_callbacks_busymod: busymod_work_func, sleeping 30 seconds ...
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Meanwhile, the livepatch is loaded. Notice that the patch transition
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does not complete as the targeted "busy" module is sitting on a
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to-be-patched function:
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% insmod samples/livepatch/livepatch-callbacks-demo.ko
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[ 113.000309] livepatch: enabling patch 'livepatch_callbacks_demo'
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[ 113.000764] livepatch: 'livepatch_callbacks_demo': initializing patching transition
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[ 113.000791] livepatch_callbacks_demo: pre_patch_callback: vmlinux
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[ 113.001289] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state
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[ 113.005208] livepatch: 'livepatch_callbacks_demo': starting patching transition
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Load a second target module (this one is an ordinary idle kernel
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module). Note that *no* post-patch callbacks will be executed while the
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livepatch is still in transition:
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% insmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 115.012740] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod'
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[ 115.013406] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
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[ 115.015315] livepatch_callbacks_mod: livepatch_callbacks_mod_init
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Request an unload of the simple kernel module. The patch is still
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transitioning, so its pre-unpatch callbacks are skipped:
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% rmmod samples/livepatch/livepatch-callbacks-mod.ko
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[ 117.022626] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
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[ 117.023376] livepatch: reverting patch 'livepatch_callbacks_demo' on unloading module 'livepatch_callbacks_mod'
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[ 117.024533] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
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Finally the livepatch is disabled. Since none of the patch's
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klp_object's post-patch callbacks executed, the remaining klp_object's
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pre-unpatch callbacks are skipped:
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% echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
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[ 119.035408] livepatch: 'livepatch_callbacks_demo': reversing transition from patching to unpatching
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[ 119.035485] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
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[ 119.711166] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
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[ 119.714179] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
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[ 119.714653] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state
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[ 119.715437] livepatch: 'livepatch_callbacks_demo': unpatching complete
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% rmmod samples/livepatch/livepatch-callbacks-demo.ko
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% rmmod samples/livepatch/livepatch-callbacks-busymod.ko
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[ 141.279111] livepatch_callbacks_busymod: busymod_work_func exit
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[ 141.279760] livepatch_callbacks_busymod: livepatch_callbacks_mod_exit
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