When livepatch tries to patch a function it takes the function address and asks ftrace to install the livepatch handler at that location. ftrace will look for an mcount call site at that exact address. On powerpc the mcount location is not the first instruction of the function, and in fact it's not at a constant offset from the start of the function. To accommodate this add a hook which arch code can override to customise the behaviour.
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| @@ -298,6 +298,19 @@ unlock: · 297 unmodified lines | ||
| 298 | 298 | rcu_read_unlock(); |
| 299 | 299 | } |
| 300 | 300 | |
| 301 | +/* | |
| 302 | + * Convert a function address into the appropriate ftrace location. | |
| 303 | + * | |
| 304 | + * Usually this is just the address of the function, but on some architectures | |
| 305 | + * it's more complicated so allow them to provide a custom behaviour. | |
| 306 | + */ | |
| 307 | +#ifndef klp_get_ftrace_location | |
| 308 | +static unsigned long klp_get_ftrace_location(unsigned long faddr) | |
| 309 | +{ | |
| 310 | + return faddr; | |
| 311 | +} | |
| 312 | +#endif | |
| 313 | + | |
| 301 | 314 | static void klp_disable_func(struct klp_func *func) |
| 302 | 315 | { |
| 303 | 316 | struct klp_ops *ops; |
| @@ -312,8 +325,14 @@ static void klp_disable_func(struct klp_func *func) · 8 unmodified lines | ||
| 312 | 325 | return; |
| 313 | 326 | |
| 314 | 327 | if (list_is_singular(&ops->func_stack)) { |
| 328 | + unsigned long ftrace_loc; | |
| 329 | + | |
| 330 | + ftrace_loc = klp_get_ftrace_location(func->old_addr); | |
| 331 | + if (WARN_ON(!ftrace_loc)) | |
| 332 | + return; | |
| 333 | + | |
| 315 | 334 | WARN_ON(unregister_ftrace_function(&ops->fops)); |
| 316 | − WARN_ON(ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0)); | |
| 335 | + WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0)); | |
| 317 | 336 | |
| 318 | 337 | list_del_rcu(&func->stack_node); |
| 319 | 338 | list_del(&ops->node); |
| @@ -338,6 +357,15 @@ static int klp_enable_func(struct klp_func *func) · 18 unmodified lines | ||
| 338 | 357 | |
| 339 | 358 | ops = klp_find_ops(func->old_addr); |
| 340 | 359 | if (!ops) { |
| 360 | + unsigned long ftrace_loc; | |
| 361 | + | |
| 362 | + ftrace_loc = klp_get_ftrace_location(func->old_addr); | |
| 363 | + if (!ftrace_loc) { | |
| 364 | + pr_err("failed to find location for function '%s'\n", | |
| 365 | + func->old_name); | |
| 366 | + return -EINVAL; | |
| 367 | + } | |
| 368 | + | |
| 341 | 369 | ops = kzalloc(sizeof(*ops), GFP_KERNEL); |
| 342 | 370 | if (!ops) |
| 343 | 371 | return -ENOMEM; |
| @@ -352,7 +380,7 @@ static int klp_enable_func(struct klp_func *func) · 8 unmodified lines | ||
| 352 | 380 | INIT_LIST_HEAD(&ops->func_stack); |
| 353 | 381 | list_add_rcu(&func->stack_node, &ops->func_stack); |
| 354 | 382 | |
| 355 | − ret = ftrace_set_filter_ip(&ops->fops, func->old_addr, 0, 0); | |
| 383 | + ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0); | |
| 356 | 384 | if (ret) { |
| 357 | 385 | pr_err("failed to set ftrace filter for function '%s' (%d)\n", |
| 358 | 386 | func->old_name, ret); |
| @@ -363,7 +391,7 @@ static int klp_enable_func(struct klp_func *func) · 4 unmodified lines | ||
| 363 | 391 | if (ret) { |
| 364 | 392 | pr_err("failed to register ftrace handler for function '%s' (%d)\n", |
| 365 | 393 | func->old_name, ret); |
| 366 | − ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0); | |
| 394 | + ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0); | |
| 367 | 395 | goto err; |
| 368 | 396 | } |
| 369 | 397 | |