1====================== 2(Un)patching Callbacks 3====================== 4 5Livepatch (un)patch-callbacks provide a mechanism for livepatch modules 6to execute callback functions when a kernel object is (un)patched. They 7can be considered a "power feature" that extends livepatching abilities 8to include: 9 10 - Safe updates to global data 11 12 - "Patches" to init and probe functions 13 14 - Patching otherwise unpatchable code (i.e. assembly) 15 16In most cases, (un)patch callbacks will need to be used in conjunction 17with memory barriers and kernel synchronization primitives, like 18mutexes/spinlocks, or even stop_machine(), to avoid concurrency issues. 19 20Callbacks differ from existing kernel facilities: 21 22 - Module init/exit code doesn't run when disabling and re-enabling a 23 patch. 24 25 - A module notifier can't stop a to-be-patched module from loading. 26 27Callbacks are part of the klp_object structure and their implementation 28is specific to that klp_object. Other livepatch objects may or may not 29be patched, irrespective of the target klp_object's current state. 30 31Callbacks can be registered for the following livepatch actions: 32 33 * Pre-patch - before a klp_object is patched 34 35 * Post-patch - after a klp_object has been patched and is active 36 across all tasks 37 38 * Pre-unpatch - before a klp_object is unpatched (ie, patched code is 39 active), used to clean up post-patch callback 40 resources 41 42 * Post-unpatch - after a klp_object has been patched, all code has 43 been restored and no tasks are running patched code, 44 used to cleanup pre-patch callback resources 45 46Each callback is optional, omitting one does not preclude specifying any 47other. However, the livepatching core executes the handlers in 48symmetry: pre-patch callbacks have a post-unpatch counterpart and 49post-patch callbacks have a pre-unpatch counterpart. An unpatch 50callback will only be executed if its corresponding patch callback was 51executed. Typical use cases pair a patch handler that acquires and 52configures resources with an unpatch handler tears down and releases 53those same resources. 54 55A callback is only executed if its host klp_object is loaded. For 56in-kernel vmlinux targets, this means that callbacks will always execute 57when a livepatch is enabled/disabled. For patch target kernel modules, 58callbacks will only execute if the target module is loaded. When a 59module target is (un)loaded, its callbacks will execute only if the 60livepatch module is enabled. 61 62The pre-patch callback, if specified, is expected to return a status 63code (0 for success, -ERRNO on error). An error status code indicates 64to the livepatching core that patching of the current klp_object is not 65safe and to stop the current patching request. (When no pre-patch 66callback is provided, the transition is assumed to be safe.) If a 67pre-patch callback returns failure, the kernel's module loader will: 68 69 - Refuse to load a livepatch, if the livepatch is loaded after 70 targeted code. 71 72 or: 73 74 - Refuse to load a module, if the livepatch was already successfully 75 loaded. 76 77No post-patch, pre-unpatch, or post-unpatch callbacks will be executed 78for a given klp_object if the object failed to patch, due to a failed 79pre_patch callback or for any other reason. 80 81If a patch transition is reversed, no pre-unpatch handlers will be run 82(this follows the previously mentioned symmetry -- pre-unpatch callbacks 83will only occur if their corresponding post-patch callback executed). 84 85If the object did successfully patch, but the patch transition never 86started for some reason (e.g., if another object failed to patch), 87only the post-unpatch callback will be called. 88 89 90Example Use-cases 91================= 92 93Update global data 94------------------ 95 96A pre-patch callback can be useful to update a global variable. For 97example, 75ff39ccc1bd ("tcp: make challenge acks less predictable") 98changes a global sysctl, as well as patches the tcp_send_challenge_ack() 99function. 100 101In this case, if we're being super paranoid, it might make sense to 102patch the data *after* patching is complete with a post-patch callback, 103so that tcp_send_challenge_ack() could first be changed to read 104sysctl_tcp_challenge_ack_limit with READ_ONCE. 105 106 107Support __init and probe function patches 108----------------------------------------- 109 110Although __init and probe functions are not directly livepatch-able, it 111may be possible to implement similar updates via pre/post-patch 112callbacks. 113 11448900cb6af42 ("virtio-net: drop NETIF_F_FRAGLIST") change the way that 115virtnet_probe() initialized its driver's net_device features. A 116pre/post-patch callback could iterate over all such devices, making a 117similar change to their hw_features value. (Client functions of the 118value may need to be updated accordingly.) 119 120 121Test cases 122========== 123 124What follows is not an exhaustive test suite of every possible livepatch 125pre/post-(un)patch combination, but a selection that demonstrates a few 126important concepts. Each test case uses the kernel modules located in 127the samples/livepatch/ and assumes that no livepatches are loaded at the 128beginning of the test. 129 130 131Test 1 132------ 133 134Test a combination of loading a kernel module and a livepatch that 135patches a function in the first module. (Un)load the target module 136before the livepatch module: 137 138- load target module 139- load livepatch 140- disable livepatch 141- unload target module 142- unload livepatch 143 144First load a target module: 145 146 % insmod samples/livepatch/livepatch-callbacks-mod.ko 147 [ 34.475708] livepatch_callbacks_mod: livepatch_callbacks_mod_init 148 149On livepatch enable, before the livepatch transition starts, pre-patch 150callbacks are executed for vmlinux and livepatch_callbacks_mod (those 151klp_objects currently loaded). After klp_objects are patched according 152to the klp_patch, their post-patch callbacks run and the transition 153completes: 154 155 % insmod samples/livepatch/livepatch-callbacks-demo.ko 156 [ 36.503719] livepatch: enabling patch 'livepatch_callbacks_demo' 157 [ 36.504213] livepatch: 'livepatch_callbacks_demo': initializing patching transition 158 [ 36.504238] livepatch_callbacks_demo: pre_patch_callback: vmlinux 159 [ 36.504721] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state 160 [ 36.505849] livepatch: 'livepatch_callbacks_demo': starting patching transition 161 [ 37.727133] livepatch: 'livepatch_callbacks_demo': completing patching transition 162 [ 37.727232] livepatch_callbacks_demo: post_patch_callback: vmlinux 163 [ 37.727860] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state 164 [ 37.728792] livepatch: 'livepatch_callbacks_demo': patching complete 165 166Similarly, on livepatch disable, pre-patch callbacks run before the 167unpatching transition starts. klp_objects are reverted, post-patch 168callbacks execute and the transition completes: 169 170 % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled 171 [ 38.510209] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition 172 [ 38.510234] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux 173 [ 38.510982] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state 174 [ 38.512209] livepatch: 'livepatch_callbacks_demo': starting unpatching transition 175 [ 39.711132] livepatch: 'livepatch_callbacks_demo': completing unpatching transition 176 [ 39.711210] livepatch_callbacks_demo: post_unpatch_callback: vmlinux 177 [ 39.711779] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state 178 [ 39.712735] livepatch: 'livepatch_callbacks_demo': unpatching complete 179 180 % rmmod samples/livepatch/livepatch-callbacks-demo.ko 181 % rmmod samples/livepatch/livepatch-callbacks-mod.ko 182 [ 42.534183] livepatch_callbacks_mod: livepatch_callbacks_mod_exit 183 184 185Test 2 186------ 187 188This test is similar to the previous test, but (un)load the livepatch 189module before the target kernel module. This tests the livepatch core's 190module_coming handler: 191 192- load livepatch 193- load target module 194- disable livepatch 195- unload livepatch 196- unload target module 197 198 199On livepatch enable, only pre/post-patch callbacks are executed for 200currently loaded klp_objects, in this case, vmlinux: 201 202 % insmod samples/livepatch/livepatch-callbacks-demo.ko 203 [ 44.553328] livepatch: enabling patch 'livepatch_callbacks_demo' 204 [ 44.553997] livepatch: 'livepatch_callbacks_demo': initializing patching transition 205 [ 44.554049] livepatch_callbacks_demo: pre_patch_callback: vmlinux 206 [ 44.554845] livepatch: 'livepatch_callbacks_demo': starting patching transition 207 [ 45.727128] livepatch: 'livepatch_callbacks_demo': completing patching transition 208 [ 45.727212] livepatch_callbacks_demo: post_patch_callback: vmlinux 209 [ 45.727961] livepatch: 'livepatch_callbacks_demo': patching complete 210 211When a targeted module is subsequently loaded, only its pre/post-patch 212callbacks are executed: 213 214 % insmod samples/livepatch/livepatch-callbacks-mod.ko 215 [ 46.560845] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod' 216 [ 46.561988] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init 217 [ 46.563452] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init 218 [ 46.565495] livepatch_callbacks_mod: livepatch_callbacks_mod_init 219 220On livepatch disable, all currently loaded klp_objects' (vmlinux and 221livepatch_callbacks_mod) pre/post-unpatch callbacks are executed: 222 223 % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled 224 [ 48.568885] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition 225 [ 48.568910] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux 226 [ 48.569441] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state 227 [ 48.570502] livepatch: 'livepatch_callbacks_demo': starting unpatching transition 228 [ 49.759091] livepatch: 'livepatch_callbacks_demo': completing unpatching transition 229 [ 49.759171] livepatch_callbacks_demo: post_unpatch_callback: vmlinux 230 [ 49.759742] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state 231 [ 49.760690] livepatch: 'livepatch_callbacks_demo': unpatching complete 232 233 % rmmod samples/livepatch/livepatch-callbacks-demo.ko 234 % rmmod samples/livepatch/livepatch-callbacks-mod.ko 235 [ 52.592283] livepatch_callbacks_mod: livepatch_callbacks_mod_exit 236 237 238Test 3 239------ 240 241Test loading the livepatch after a targeted kernel module, then unload 242the kernel module before disabling the livepatch. This tests the 243livepatch core's module_going handler: 244 245- load target module 246- load livepatch 247- unload target module 248- disable livepatch 249- unload livepatch 250 251First load a target module, then the livepatch: 252 253 % insmod samples/livepatch/livepatch-callbacks-mod.ko 254 [ 54.607948] livepatch_callbacks_mod: livepatch_callbacks_mod_init 255 256 % insmod samples/livepatch/livepatch-callbacks-demo.ko 257 [ 56.613919] livepatch: enabling patch 'livepatch_callbacks_demo' 258 [ 56.614411] livepatch: 'livepatch_callbacks_demo': initializing patching transition 259 [ 56.614436] livepatch_callbacks_demo: pre_patch_callback: vmlinux 260 [ 56.614818] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state 261 [ 56.615656] livepatch: 'livepatch_callbacks_demo': starting patching transition 262 [ 57.759070] livepatch: 'livepatch_callbacks_demo': completing patching transition 263 [ 57.759147] livepatch_callbacks_demo: post_patch_callback: vmlinux 264 [ 57.759621] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state 265 [ 57.760307] livepatch: 'livepatch_callbacks_demo': patching complete 266 267When a target module is unloaded, the livepatch is only reverted from 268that klp_object (livepatch_callbacks_mod). As such, only its pre and 269post-unpatch callbacks are executed when this occurs: 270 271 % rmmod samples/livepatch/livepatch-callbacks-mod.ko 272 [ 58.623409] livepatch_callbacks_mod: livepatch_callbacks_mod_exit 273 [ 58.623903] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away 274 [ 58.624658] livepatch: reverting patch 'livepatch_callbacks_demo' on unloading module 'livepatch_callbacks_mod' 275 [ 58.625305] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away 276 277When the livepatch is disabled, pre and post-unpatch callbacks are run 278for the remaining klp_object, vmlinux: 279 280 % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled 281 [ 60.638420] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition 282 [ 60.638444] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux 283 [ 60.638996] livepatch: 'livepatch_callbacks_demo': starting unpatching transition 284 [ 61.727088] livepatch: 'livepatch_callbacks_demo': completing unpatching transition 285 [ 61.727165] livepatch_callbacks_demo: post_unpatch_callback: vmlinux 286 [ 61.727985] livepatch: 'livepatch_callbacks_demo': unpatching complete 287 288 % rmmod samples/livepatch/livepatch-callbacks-demo.ko 289 290 291Test 4 292------ 293 294This test is similar to the previous test, however the livepatch is 295loaded first. This tests the livepatch core's module_coming and 296module_going handlers: 297 298- load livepatch 299- load target module 300- unload target module 301- disable livepatch 302- unload livepatch 303 304First load the livepatch: 305 306 % insmod samples/livepatch/livepatch-callbacks-demo.ko 307 [ 64.661552] livepatch: enabling patch 'livepatch_callbacks_demo' 308 [ 64.662147] livepatch: 'livepatch_callbacks_demo': initializing patching transition 309 [ 64.662175] livepatch_callbacks_demo: pre_patch_callback: vmlinux 310 [ 64.662850] livepatch: 'livepatch_callbacks_demo': starting patching transition 311 [ 65.695056] livepatch: 'livepatch_callbacks_demo': completing patching transition 312 [ 65.695147] livepatch_callbacks_demo: post_patch_callback: vmlinux 313 [ 65.695561] livepatch: 'livepatch_callbacks_demo': patching complete 314 315When a targeted kernel module is subsequently loaded, only its 316pre/post-patch callbacks are executed: 317 318 % insmod samples/livepatch/livepatch-callbacks-mod.ko 319 [ 66.669196] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod' 320 [ 66.669882] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init 321 [ 66.670744] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init 322 [ 66.672873] livepatch_callbacks_mod: livepatch_callbacks_mod_init 323 324When the target module is unloaded, the livepatch is only reverted from 325the livepatch_callbacks_mod klp_object. As such, only pre and 326post-unpatch callbacks are executed when this occurs: 327 328 % rmmod samples/livepatch/livepatch-callbacks-mod.ko 329 [ 68.680065] livepatch_callbacks_mod: livepatch_callbacks_mod_exit 330 [ 68.680688] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away 331 [ 68.681452] livepatch: reverting patch 'livepatch_callbacks_demo' on unloading module 'livepatch_callbacks_mod' 332 [ 68.682094] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away 333 334 % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled 335 [ 70.689225] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition 336 [ 70.689256] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux 337 [ 70.689882] livepatch: 'livepatch_callbacks_demo': starting unpatching transition 338 [ 71.711080] livepatch: 'livepatch_callbacks_demo': completing unpatching transition 339 [ 71.711481] livepatch_callbacks_demo: post_unpatch_callback: vmlinux 340 [ 71.711988] livepatch: 'livepatch_callbacks_demo': unpatching complete 341 342 % rmmod samples/livepatch/livepatch-callbacks-demo.ko 343 344 345Test 5 346------ 347 348A simple test of loading a livepatch without one of its patch target 349klp_objects ever loaded (livepatch_callbacks_mod): 350 351- load livepatch 352- disable livepatch 353- unload livepatch 354 355Load the livepatch: 356 357 % insmod samples/livepatch/livepatch-callbacks-demo.ko 358 [ 74.711081] livepatch: enabling patch 'livepatch_callbacks_demo' 359 [ 74.711595] livepatch: 'livepatch_callbacks_demo': initializing patching transition 360 [ 74.711639] livepatch_callbacks_demo: pre_patch_callback: vmlinux 361 [ 74.712272] livepatch: 'livepatch_callbacks_demo': starting patching transition 362 [ 75.743137] livepatch: 'livepatch_callbacks_demo': completing patching transition 363 [ 75.743219] livepatch_callbacks_demo: post_patch_callback: vmlinux 364 [ 75.743867] livepatch: 'livepatch_callbacks_demo': patching complete 365 366As expected, only pre/post-(un)patch handlers are executed for vmlinux: 367 368 % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled 369 [ 76.716254] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition 370 [ 76.716278] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux 371 [ 76.716666] livepatch: 'livepatch_callbacks_demo': starting unpatching transition 372 [ 77.727089] livepatch: 'livepatch_callbacks_demo': completing unpatching transition 373 [ 77.727194] livepatch_callbacks_demo: post_unpatch_callback: vmlinux 374 [ 77.727907] livepatch: 'livepatch_callbacks_demo': unpatching complete 375 376 % rmmod samples/livepatch/livepatch-callbacks-demo.ko 377 378 379Test 6 380------ 381 382Test a scenario where a vmlinux pre-patch callback returns a non-zero 383status (ie, failure): 384 385- load target module 386- load livepatch -ENODEV 387- unload target module 388 389First load a target module: 390 391 % insmod samples/livepatch/livepatch-callbacks-mod.ko 392 [ 80.740520] livepatch_callbacks_mod: livepatch_callbacks_mod_init 393 394Load the livepatch module, setting its 'pre_patch_ret' value to -19 395(-ENODEV). When its vmlinux pre-patch callback executed, this status 396code will propagate back to the module-loading subsystem. The result is 397that the insmod command refuses to load the livepatch module: 398 399 % insmod samples/livepatch/livepatch-callbacks-demo.ko pre_patch_ret=-19 400 [ 82.747326] livepatch: enabling patch 'livepatch_callbacks_demo' 401 [ 82.747743] livepatch: 'livepatch_callbacks_demo': initializing patching transition 402 [ 82.747767] livepatch_callbacks_demo: pre_patch_callback: vmlinux 403 [ 82.748237] livepatch: pre-patch callback failed for object 'vmlinux' 404 [ 82.748637] livepatch: failed to enable patch 'livepatch_callbacks_demo' 405 [ 82.749059] livepatch: 'livepatch_callbacks_demo': canceling transition, going to unpatch 406 [ 82.749060] livepatch: 'livepatch_callbacks_demo': completing unpatching transition 407 [ 82.749868] livepatch: 'livepatch_callbacks_demo': unpatching complete 408 [ 82.765809] insmod: ERROR: could not insert module samples/livepatch/livepatch-callbacks-demo.ko: No such device 409 410 % rmmod samples/livepatch/livepatch-callbacks-mod.ko 411 [ 84.774238] livepatch_callbacks_mod: livepatch_callbacks_mod_exit 412 413 414Test 7 415------ 416 417Similar to the previous test, setup a livepatch such that its vmlinux 418pre-patch callback returns success. However, when a targeted kernel 419module is later loaded, have the livepatch return a failing status code: 420 421- load livepatch 422- setup -ENODEV 423- load target module 424- disable livepatch 425- unload livepatch 426 427Load the livepatch, notice vmlinux pre-patch callback succeeds: 428 429 % insmod samples/livepatch/livepatch-callbacks-demo.ko 430 [ 86.787845] livepatch: enabling patch 'livepatch_callbacks_demo' 431 [ 86.788325] livepatch: 'livepatch_callbacks_demo': initializing patching transition 432 [ 86.788427] livepatch_callbacks_demo: pre_patch_callback: vmlinux 433 [ 86.788821] livepatch: 'livepatch_callbacks_demo': starting patching transition 434 [ 87.711069] livepatch: 'livepatch_callbacks_demo': completing patching transition 435 [ 87.711143] livepatch_callbacks_demo: post_patch_callback: vmlinux 436 [ 87.711886] livepatch: 'livepatch_callbacks_demo': patching complete 437 438Set a trap so subsequent pre-patch callbacks to this livepatch will 439return -ENODEV: 440 441 % echo -19 > /sys/module/livepatch_callbacks_demo/parameters/pre_patch_ret 442 443The livepatch pre-patch callback for subsequently loaded target modules 444will return failure, so the module loader refuses to load the kernel 445module. Notice that no post-patch or pre/post-unpatch callbacks are 446executed for this klp_object: 447 448 % insmod samples/livepatch/livepatch-callbacks-mod.ko 449 [ 90.796976] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod' 450 [ 90.797834] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init 451 [ 90.798900] livepatch: pre-patch callback failed for object 'livepatch_callbacks_mod' 452 [ 90.799652] livepatch: patch 'livepatch_callbacks_demo' failed for module 'livepatch_callbacks_mod', refusing to load module 'livepatch_callbacks_mod' 453 [ 90.819737] insmod: ERROR: could not insert module samples/livepatch/livepatch-callbacks-mod.ko: No such device 454 455However, pre/post-unpatch callbacks run for the vmlinux klp_object: 456 457 % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled 458 [ 92.823547] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition 459 [ 92.823573] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux 460 [ 92.824331] livepatch: 'livepatch_callbacks_demo': starting unpatching transition 461 [ 93.727128] livepatch: 'livepatch_callbacks_demo': completing unpatching transition 462 [ 93.727327] livepatch_callbacks_demo: post_unpatch_callback: vmlinux 463 [ 93.727861] livepatch: 'livepatch_callbacks_demo': unpatching complete 464 465 % rmmod samples/livepatch/livepatch-callbacks-demo.ko 466 467 468Test 8 469------ 470 471Test loading multiple targeted kernel modules. This test-case is 472mainly for comparing with the next test-case. 473 474- load busy target module (0s sleep), 475- load livepatch 476- load target module 477- unload target module 478- disable livepatch 479- unload livepatch 480- unload busy target module 481 482 483Load a target "busy" kernel module which kicks off a worker function 484that immediately exits: 485 486 % insmod samples/livepatch/livepatch-callbacks-busymod.ko sleep_secs=0 487 [ 96.910107] livepatch_callbacks_busymod: livepatch_callbacks_mod_init 488 [ 96.910600] livepatch_callbacks_busymod: busymod_work_func, sleeping 0 seconds ... 489 [ 96.913024] livepatch_callbacks_busymod: busymod_work_func exit 490 491Proceed with loading the livepatch and another ordinary target module, 492notice that the post-patch callbacks are executed and the transition 493completes quickly: 494 495 % insmod samples/livepatch/livepatch-callbacks-demo.ko 496 [ 98.917892] livepatch: enabling patch 'livepatch_callbacks_demo' 497 [ 98.918426] livepatch: 'livepatch_callbacks_demo': initializing patching transition 498 [ 98.918453] livepatch_callbacks_demo: pre_patch_callback: vmlinux 499 [ 98.918955] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state 500 [ 98.923835] livepatch: 'livepatch_callbacks_demo': starting patching transition 501 [ 99.743104] livepatch: 'livepatch_callbacks_demo': completing patching transition 502 [ 99.743156] livepatch_callbacks_demo: post_patch_callback: vmlinux 503 [ 99.743679] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state 504 [ 99.744616] livepatch: 'livepatch_callbacks_demo': patching complete 505 506 % insmod samples/livepatch/livepatch-callbacks-mod.ko 507 [ 100.930955] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod' 508 [ 100.931668] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init 509 [ 100.932645] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init 510 [ 100.934125] livepatch_callbacks_mod: livepatch_callbacks_mod_init 511 512 % rmmod samples/livepatch/livepatch-callbacks-mod.ko 513 [ 102.942805] livepatch_callbacks_mod: livepatch_callbacks_mod_exit 514 [ 102.943640] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away 515 [ 102.944585] livepatch: reverting patch 'livepatch_callbacks_demo' on unloading module 'livepatch_callbacks_mod' 516 [ 102.945455] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away 517 518 % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled 519 [ 104.953815] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition 520 [ 104.953838] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux 521 [ 104.954431] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state 522 [ 104.955426] livepatch: 'livepatch_callbacks_demo': starting unpatching transition 523 [ 106.719073] livepatch: 'livepatch_callbacks_demo': completing unpatching transition 524 [ 106.722633] livepatch_callbacks_demo: post_unpatch_callback: vmlinux 525 [ 106.723282] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state 526 [ 106.724279] livepatch: 'livepatch_callbacks_demo': unpatching complete 527 528 % rmmod samples/livepatch/livepatch-callbacks-demo.ko 529 % rmmod samples/livepatch/livepatch-callbacks-busymod.ko 530 [ 108.975660] livepatch_callbacks_busymod: livepatch_callbacks_mod_exit 531 532 533Test 9 534------ 535 536A similar test as the previous one, but force the "busy" kernel module 537to do longer work. 538 539The livepatching core will refuse to patch a task that is currently 540executing a to-be-patched function -- the consistency model stalls the 541current patch transition until this safety-check is met. Test a 542scenario where one of a livepatch's target klp_objects sits on such a 543function for a long time. Meanwhile, load and unload other target 544kernel modules while the livepatch transition is in progress. 545 546- load busy target module (30s sleep) 547- load livepatch 548- load target module 549- unload target module 550- disable livepatch 551- unload livepatch 552- unload busy target module 553 554 555Load the "busy" kernel module, this time make it do 30 seconds worth of 556work: 557 558 % insmod samples/livepatch/livepatch-callbacks-busymod.ko sleep_secs=30 559 [ 110.993362] livepatch_callbacks_busymod: livepatch_callbacks_mod_init 560 [ 110.994059] livepatch_callbacks_busymod: busymod_work_func, sleeping 30 seconds ... 561 562Meanwhile, the livepatch is loaded. Notice that the patch transition 563does not complete as the targeted "busy" module is sitting on a 564to-be-patched function: 565 566 % insmod samples/livepatch/livepatch-callbacks-demo.ko 567 [ 113.000309] livepatch: enabling patch 'livepatch_callbacks_demo' 568 [ 113.000764] livepatch: 'livepatch_callbacks_demo': initializing patching transition 569 [ 113.000791] livepatch_callbacks_demo: pre_patch_callback: vmlinux 570 [ 113.001289] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state 571 [ 113.005208] livepatch: 'livepatch_callbacks_demo': starting patching transition 572 573Load a second target module (this one is an ordinary idle kernel 574module). Note that *no* post-patch callbacks will be executed while the 575livepatch is still in transition: 576 577 % insmod samples/livepatch/livepatch-callbacks-mod.ko 578 [ 115.012740] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod' 579 [ 115.013406] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init 580 [ 115.015315] livepatch_callbacks_mod: livepatch_callbacks_mod_init 581 582Request an unload of the simple kernel module. The patch is still 583transitioning, so its pre-unpatch callbacks are skipped: 584 585 % rmmod samples/livepatch/livepatch-callbacks-mod.ko 586 [ 117.022626] livepatch_callbacks_mod: livepatch_callbacks_mod_exit 587 [ 117.023376] livepatch: reverting patch 'livepatch_callbacks_demo' on unloading module 'livepatch_callbacks_mod' 588 [ 117.024533] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away 589 590Finally the livepatch is disabled. Since none of the patch's 591klp_object's post-patch callbacks executed, the remaining klp_object's 592pre-unpatch callbacks are skipped: 593 594 % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled 595 [ 119.035408] livepatch: 'livepatch_callbacks_demo': reversing transition from patching to unpatching 596 [ 119.035485] livepatch: 'livepatch_callbacks_demo': starting unpatching transition 597 [ 119.711166] livepatch: 'livepatch_callbacks_demo': completing unpatching transition 598 [ 119.714179] livepatch_callbacks_demo: post_unpatch_callback: vmlinux 599 [ 119.714653] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state 600 [ 119.715437] livepatch: 'livepatch_callbacks_demo': unpatching complete 601 602 % rmmod samples/livepatch/livepatch-callbacks-demo.ko 603 % rmmod samples/livepatch/livepatch-callbacks-busymod.ko 604 [ 141.279111] livepatch_callbacks_busymod: busymod_work_func exit 605 [ 141.279760] livepatch_callbacks_busymod: livepatch_callbacks_mod_exit 606
