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linux/Documentation/livepatch/callbacks.txt
Joe Lawrence 93862e385d livepatch: add (un)patch callbacks 
Provide livepatch modules a klp_object (un)patching notification
mechanism.  Pre and post-(un)patch callbacks allow livepatch modules to
setup or synchronize changes that would be difficult to support in only
patched-or-unpatched code contexts.

Callbacks can be registered for target module or vmlinux klp_objects,
but each implementation is klp_object specific.

  - Pre-(un)patch callbacks run before any (un)patching transition
    starts.

  - Post-(un)patch callbacks run once an object has been (un)patched and
    the klp_patch fully transitioned to its target state.

Example use cases include modification of global data and registration
of newly available services/handlers.

See Documentation/livepatch/callbacks.txt for details and
samples/livepatch/ for examples.

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2017-10-19 10:08:56 +02:00

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