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uprobes-inode.c
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/* -*- linux-c -*- * Common functions for using inode-based uprobes * Copyright (C) 2011-2013,2015 Red Hat Inc. * * This file is part of systemtap, and is free software. You can * redistribute it and/or modify it under the terms of the GNU General * Public License (GPL); either version 2, or (at your option) any * later version. */ #ifndef _UPROBES_INODE_C_ #define _UPROBES_INODE_C_ #include <linux/fs.h> #include <linux/list.h> #include <linux/namei.h> #include <linux/mutex.h> #include <linux/spinlock.h> #include <linux/uprobes.h> /* STAPIU: SystemTap Inode Uprobes */ // PR13489, inodes-uprobes export kludge #if !defined(CONFIG_UPROBES) #error "not to be built without CONFIG_UPROBES" #endif #if !defined(STAPCONF_UPROBE_REGISTER_EXPORTED) // First get the right typeof(name) that's found in uprobes.h #if defined(STAPCONF_OLD_INODE_UPROBES) typedef typeof(®ister_uprobe) uprobe_register_fn; #else typedef typeof(&uprobe_register) uprobe_register_fn; #endif // Then define the typecasted call via function pointer #define uprobe_register (* (uprobe_register_fn)kallsyms_uprobe_register) #elif defined(STAPCONF_OLD_INODE_UPROBES) // In this case, just need to map the new name to the old #define uprobe_register register_uprobe #endif #if !defined(STAPCONF_UPROBE_UNREGISTER_EXPORTED) // First get the right typeof(name) that's found in uprobes.h #if defined(STAPCONF_OLD_INODE_UPROBES) typedef typeof(&unregister_uprobe) uprobe_unregister_fn; #else typedef typeof(&uprobe_unregister) uprobe_unregister_fn; #endif // Then define the typecasted call via function pointer #define uprobe_unregister (* (uprobe_unregister_fn)kallsyms_uprobe_unregister) #elif defined(STAPCONF_OLD_INODE_UPROBES) // In this case, just need to map the new name to the old #define uprobe_unregister unregister_uprobe #endif // uprobes started setting REG_IP itself starting in kernel commit 74e59dfc. // There's no direct indicator of this, but commit da1816b1 in the same patch // series defines UPROBE_HANDLER_MASK, so that's a decent trigger for us. #ifndef UPROBE_HANDLER_MASK #define STAPIU_NEEDS_REG_IP 1 #if !defined(STAPCONF_UPROBE_GET_SWBP_ADDR_EXPORTED) // First typedef from the original decl, then #define it as a typecasted call. typedef typeof(&uprobe_get_swbp_addr) uprobe_get_swbp_addr_fn; #define uprobe_get_swbp_addr (* (uprobe_get_swbp_addr_fn)kallsyms_uprobe_get_swbp_addr) #endif #endif /* A target is a specific file/inode that we want to probe. */ struct stapiu_target { /* All the uprobes for this target. */ struct list_head consumers; /* stapiu_consumer */ /* All the processes containing this target. * This may not be system-wide, e.g. only the -c process. * We use task_finder to manage this list. */ struct list_head processes; /* stapiu_process */ rwlock_t process_lock; struct stap_task_finder_target finder; const char * const filename; struct inode *inode; struct mutex inode_lock; }; /* A consumer is a specific uprobe that we want to place. */ struct stapiu_consumer { struct uprobe_consumer consumer; const unsigned return_p:1; unsigned registered:1; struct list_head target_consumer; struct stapiu_target * const target; loff_t offset; /* the probe offset within the inode */ loff_t sdt_sem_offset; /* the semaphore offset from process->base */ // List of perf counters used by each probe // This list is an index into struct stap_perf_probe, long perf_counters_dim; long *perf_counters; void (*perf_read_handler)(long *values); const struct stap_probe * const probe; }; /* A process that we want to probe. These are dynamically discovered and * associated using task_finder, allocated from this static array. */ static struct stapiu_process { struct list_head target_process; unsigned long relocation; /* the mmap'ed .text address */ unsigned long base; /* the address to apply sdt offsets against */ pid_t tgid; } stapiu_process_slots[MAXUPROBES]; /* This lock guards modification to stapiu_process_slots. * Note: target->process_lock nests inside this. */ static DEFINE_SPINLOCK(stapiu_process_slots_lock); #if defined(UPROBES_HITCOUNT) static atomic_t prehandler_hitcount = ATOMIC_INIT(0); static atomic_t handler_hitcount = ATOMIC_INIT(0); #endif /* The stap-generated probe handler for all inode-uprobes. */ static int stapiu_probe_handler (struct stapiu_consumer *sup, struct pt_regs *regs); static int stapiu_probe_prehandler (struct uprobe_consumer *inst, struct pt_regs *regs) { int ret; struct stapiu_consumer *sup = container_of(inst, struct stapiu_consumer, consumer); struct stapiu_target *target = sup->target; struct stapiu_process *p, *process = NULL; #if defined(UPROBES_HITCOUNT) atomic_inc(&prehandler_hitcount); #endif /* First find the related process, set by stapiu_change_plus. * NB: This is a linear search performed for every probe hit! * This could be an algorithmic problem if the list gets large, but * we'll wait until this is demonstratedly a hotspot before optimizing. */ read_lock(&target->process_lock); list_for_each_entry(p, &target->processes, target_process) { if (p->tgid == current->tgid) { process = p; break; } } read_unlock(&target->process_lock); if (!process) { #ifdef UPROBE_HANDLER_REMOVE /* Once we're past the starting phase, we can be sure that any * processes which are executing code in a mapping have already * been through task_finder. So if it's not in our list of * target->processes, it can safely get removed. */ if (stap_task_finder_complete()) return UPROBE_HANDLER_REMOVE; #endif return 0; } #ifdef STAPIU_NEEDS_REG_IP /* Make it look like the IP is set as it would in the actual user task * before calling the real probe handler. */ { unsigned long saved_ip = REG_IP(regs); SET_REG_IP(regs, uprobe_get_swbp_addr(regs)); #endif #if defined(UPROBES_HITCOUNT) atomic_inc(&handler_hitcount); #endif ret = stapiu_probe_handler(sup, regs); #ifdef STAPIU_NEEDS_REG_IP /* Reset IP regs on return, so we don't confuse uprobes. */ SET_REG_IP(regs, saved_ip); } #endif return ret; } static int stapiu_retprobe_prehandler (struct uprobe_consumer *inst, unsigned long func __attribute__((unused)), struct pt_regs *regs) { return stapiu_probe_prehandler(inst, regs); } static int stapiu_register (struct inode* inode, struct stapiu_consumer* c) { int ret = 0; if (!c->return_p) { c->consumer.handler = stapiu_probe_prehandler; } else { #if defined(STAPCONF_INODE_URETPROBES) c->consumer.ret_handler = stapiu_retprobe_prehandler; #else ret = EINVAL; #endif } if (ret == 0) ret = uprobe_register (inode, c->offset, &c->consumer); c->registered = (ret ? 0 : 1); return ret; } static void stapiu_unregister (struct inode* inode, struct stapiu_consumer* c) { uprobe_unregister (inode, c->offset, &c->consumer); c->registered = 0; } static inline void stapiu_target_lock(struct stapiu_target *target) { might_sleep(); mutex_lock(&target->inode_lock); } static inline void stapiu_target_unlock(struct stapiu_target *target) { mutex_unlock(&target->inode_lock); } /* Read-modify-write a semaphore, usually +/- 1. */ static int stapiu_write_semaphore(unsigned long addr, unsigned short delta) { int rc = 0; unsigned short __user* sdt_addr = (unsigned short __user*) addr; unsigned short sdt_semaphore = 0; /* NB: fixed size */ /* XXX: need to analyze possibility of race condition */ rc = get_user(sdt_semaphore, sdt_addr); if (!rc) { sdt_semaphore += delta; rc = put_user(sdt_semaphore, sdt_addr); } return rc; } /* Read-modify-write a semaphore in an arbitrary task, usually +/- 1. */ static int stapiu_write_task_semaphore(struct task_struct* task, unsigned long addr, unsigned short delta) { int count, rc = 0; unsigned short sdt_semaphore = 0; /* NB: fixed size */ /* XXX: need to analyze possibility of race condition */ count = __access_process_vm_noflush(task, addr, &sdt_semaphore, sizeof(sdt_semaphore), 0); if (count != sizeof(sdt_semaphore)) rc = 1; else { sdt_semaphore += delta; count = __access_process_vm_noflush(task, addr, &sdt_semaphore, sizeof(sdt_semaphore), 1); rc = (count == sizeof(sdt_semaphore)) ? 0 : 1; } return rc; } static void stapiu_decrement_process_semaphores(struct stapiu_process *p, struct list_head *consumers) { struct task_struct *task; rcu_read_lock(); #if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,24) /* We'd like to call find_task_by_pid_ns() here, but it isn't * exported. So, we call what it calls... */ task = pid_task(find_pid_ns(p->tgid, &init_pid_ns), PIDTYPE_PID); #else task = find_task_by_pid(p->tgid); #endif /* The task may have exited while we weren't watching. */ if (task) { struct stapiu_consumer *c; /* Holding the rcu read lock makes us atomic, and we * can't write userspace memory while atomic (which * could pagefault). So, instead we lock the task * structure, then release the rcu read lock. */ get_task_struct(task); rcu_read_unlock(); list_for_each_entry(c, consumers, target_consumer) { if (c->sdt_sem_offset) { unsigned long addr = p->base + c->sdt_sem_offset; stapiu_write_task_semaphore(task, addr, (unsigned short) -1); } } put_task_struct(task); } else { rcu_read_unlock(); } } /* As part of shutdown, we need to decrement the semaphores in every task we've * been attached to. */ static void stapiu_decrement_semaphores(struct stapiu_target *targets, size_t ntargets) { size_t i; /* NB: no stapiu_process_slots_lock needed, as the task_finder engine is * already stopped by now, so no one else will mess with us. We need * to be sleepable for access_process_vm. */ might_sleep(); for (i = 0; i < ntargets; ++i) { struct stapiu_target *ut = &targets[i]; struct stapiu_consumer *c; struct stapiu_process *p; int has_semaphores = 0; list_for_each_entry(c, &ut->consumers, target_consumer) { if (c->sdt_sem_offset) { has_semaphores = 1; break; } } if (!has_semaphores) continue; list_for_each_entry(p, &ut->processes, target_process) stapiu_decrement_process_semaphores(p, &ut->consumers); } } /* Unregister all uprobe consumers of a target. */ static void stapiu_target_unreg(struct stapiu_target *target) { struct stapiu_consumer *c; if (! target->inode) return; list_for_each_entry(c, &target->consumers, target_consumer) { if (c->registered) stapiu_unregister(target->inode, c); } } /* Register all uprobe consumers of a target. */ static int stapiu_target_reg(struct stapiu_target *target, struct task_struct* task) { int ret = 0; struct stapiu_consumer *c; list_for_each_entry(c, &target->consumers, target_consumer) { if (! c->registered) { int i; for (i=0; i < c->perf_counters_dim; i++) { if ((c->perf_counters)[i] > -1) _stp_perf_read_init ((c->perf_counters)[i], task); } if (!c->probe->cond_enabled) { dbug_otf("not registering (u%sprobe) pidx %zu\n", c->return_p ? "ret" : "", c->probe->index); continue; } ret = stapiu_register(target->inode, c); if (ret != 0) _stp_warn("probe %s inode-offset %p registration error (rc %d)", c->probe->pp, (void*) (uintptr_t) c->offset, ret); } } if (ret) stapiu_target_unreg(target); return ret; } /* Register/unregister a target's uprobe consumers if their associated probe * handlers have their conditions enabled/disabled. */ static void stapiu_target_refresh(struct stapiu_target *target) { struct stapiu_consumer *c; // go through every consumer list_for_each_entry(c, &target->consumers, target_consumer) { // should we unregister it? if (c->registered && !c->probe->cond_enabled) { dbug_otf("unregistering (u%sprobe) pidx %zu\n", c->return_p ? "ret" : "", c->probe->index); stapiu_unregister(target->inode, c); // should we register it? } else if (!c->registered && c->probe->cond_enabled) { dbug_otf("registering (u%sprobe) pidx %zu\n", c->return_p ? "ret" : "", c->probe->index); if (stapiu_register(target->inode, c) != 0) dbug_otf("couldn't register (u%sprobe) pidx %zu\n", c->return_p ? "ret" : "", c->probe->index); } } } /* Cleanup every target. */ static void stapiu_exit_targets(struct stapiu_target *targets, size_t ntargets) { size_t i; for (i = 0; i < ntargets; ++i) { struct stapiu_target *ut = &targets[i]; stapiu_target_unreg(ut); /* NB: task_finder needs no unregister. */ if (ut->inode) { iput(ut->inode); ut->inode = NULL; } } } /* Initialize every target. */ static int stapiu_init_targets(struct stapiu_target *targets, size_t ntargets) { int ret = 0; size_t i; for (i = 0; i < ntargets; ++i) { struct stapiu_target *ut = &targets[i]; INIT_LIST_HEAD(&ut->consumers); INIT_LIST_HEAD(&ut->processes); rwlock_init(&ut->process_lock); mutex_init(&ut->inode_lock); ret = stap_register_task_finder_target(&ut->finder); if (ret != 0) { _stp_error("Couldn't register task finder target for file '%s': %d\n", ut->filename, ret); break; } } return ret; } /* Initialize the entire inode-uprobes subsystem. */ static int stapiu_init(struct stapiu_target *targets, size_t ntargets, struct stapiu_consumer *consumers, size_t nconsumers) { int ret = stapiu_init_targets(targets, ntargets); if (!ret) { size_t i; /* Connect each consumer to its target. */ for (i = 0; i < nconsumers; ++i) { struct stapiu_consumer *uc = &consumers[i]; list_add(&uc->target_consumer, &uc->target->consumers); } } return ret; } /* Refresh the entire inode-uprobes subsystem. */ static void stapiu_refresh(struct stapiu_target *targets, size_t ntargets) { size_t i; for (i = 0; i < ntargets; ++i) { struct stapiu_target *target = &targets[i]; // we need to lock it to ensure probes don't get // registered under our feet stapiu_target_lock(target); if (target->inode) stapiu_target_refresh(target); stapiu_target_unlock(target); } } /* Shutdown the entire inode-uprobes subsystem. */ static void stapiu_exit(struct stapiu_target *targets, size_t ntargets, struct stapiu_consumer *consumers, size_t nconsumers) { stapiu_decrement_semaphores(targets, ntargets); stapiu_exit_targets(targets, ntargets); #if defined(UPROBES_HITCOUNT) _stp_printf("stapiu_probe_prehandler() called %d times\n", atomic_read(&prehandler_hitcount)); _stp_printf("stapiu_probe_handler() called %d times\n", atomic_read(&handler_hitcount)); _stp_print_flush(); #endif } /* Task-finder found a process with the target that we're interested in. * Grab a process slot and associate with this target, so the semaphores * and filtering can work properly. */ static int stapiu_change_plus(struct stapiu_target* target, struct task_struct *task, unsigned long relocation, unsigned long length, unsigned long offset, unsigned long vm_flags, struct inode *inode) { size_t i; struct stapiu_process *p; int rc; /* Check the buildid of the target (if we haven't already). We * lock the target so we don't have concurrency issues. */ stapiu_target_lock(target); if (! target->inode) { if (! inode) { rc = -EINVAL; stapiu_target_unlock(target); return rc; } /* Grab the inode first (to prevent TOCTTOU problems). */ target->inode = igrab(inode); if (!target->inode) { _stp_error("Couldn't get inode for file '%s'\n", target->filename); rc = -EINVAL; stapiu_target_unlock(target); return rc; } /* Actually do the check. */ if ((rc = _stp_usermodule_check(task, target->filename, relocation))) { /* Be sure to release the inode on failure. */ iput(target->inode); target->inode = NULL; stapiu_target_unlock(target); return rc; } /* OK, we've checked the target's buildid. Now * register all its consumers. */ rc = stapiu_target_reg(target, task); if (rc) { /* Be sure to release the inode on failure. */ iput(target->inode); target->inode = NULL; stapiu_target_unlock(target); return rc; } } stapiu_target_unlock(target); /* Associate this target with this process. */ spin_lock(&stapiu_process_slots_lock); write_lock(&target->process_lock); for (i = 0; i < MAXUPROBES; ++i) { p = &stapiu_process_slots[i]; if (!p->tgid) { p->tgid = task->tgid; p->relocation = relocation; /* The base is used for relocating semaphores. If the * probe is in an ET_EXEC binary, then that offset * already is a real address. But stapiu_process_found * calls us in this case with relocation=offset=0, so * we don't have to worry about it. */ p->base = relocation - offset; list_add(&p->target_process, &target->processes); break; } } write_unlock(&target->process_lock); spin_unlock(&stapiu_process_slots_lock); return 0; /* XXX: or an error? maxskipped? */ } /* Task-finder found a writable mapping in our interested target. * If any of the consumers need a semaphore, increment now. */ static int stapiu_change_semaphore_plus(struct stapiu_target* target, struct task_struct *task, unsigned long relocation, unsigned long length) { int rc = 0; struct stapiu_process *p, *process = NULL; struct stapiu_consumer *c; /* First find the related process, set by stapiu_change_plus. */ read_lock(&target->process_lock); list_for_each_entry(p, &target->processes, target_process) { if (p->tgid == task->tgid) { process = p; break; } } read_unlock(&target->process_lock); if (!process) return 0; /* NB: no lock after this point, as we need to be sleepable for * get/put_user semaphore action. The given process should be frozen * while we're busy, so it's not an issue. */ /* Look through all the consumers and increment semaphores. */ list_for_each_entry(c, &target->consumers, target_consumer) { if (c->sdt_sem_offset) { unsigned long addr = process->base + c->sdt_sem_offset; if (addr >= relocation && addr < relocation + length) { int rc2 = stapiu_write_task_semaphore(task, addr, +1); if (!rc) rc = rc2; } } } return rc; } /* Task-finder found a mapping that's now going away. We don't need to worry * about the semaphores, so we can just release the process slot. */ static int stapiu_change_minus(struct stapiu_target* target, struct task_struct *task, unsigned long relocation, unsigned long length) { struct stapiu_process *p, *tmp; /* NB: we aren't unregistering uprobes and releasing the * inode here. The registration is system-wide, based on * inode, not process based. */ spin_lock(&stapiu_process_slots_lock); write_lock(&target->process_lock); list_for_each_entry_safe(p, tmp, &target->processes, target_process) { if (p->tgid == task->tgid && (relocation <= p->relocation && p->relocation < relocation+length)) { list_del(&p->target_process); memset(p, 0, sizeof(*p)); } } write_unlock(&target->process_lock); spin_unlock(&stapiu_process_slots_lock); return 0; } static struct inode * stapiu_get_task_inode(struct task_struct *task) { struct mm_struct *mm; struct file* vm_file; struct inode *inode = NULL; // Grab the inode associated with the task. // // Note we're not calling get_task_mm()/mmput() here. Since // we're in the the context of task, the mm should stick // around without locking it (and mmput() can sleep). mm = task->mm; if (! mm) { /* If the thread doesn't have a mm_struct, it is * a kernel thread which we need to skip. */ return NULL; } vm_file = stap_find_exe_file(mm); if (vm_file) { if (vm_file->f_path.dentry) inode = vm_file->f_path.dentry->d_inode; fput(vm_file); } return inode; } /* The task_finder_callback we use for ET_EXEC targets. */ static int stapiu_process_found(struct stap_task_finder_target *tf_target, struct task_struct *task, int register_p, int process_p) { struct stapiu_target *target = container_of(tf_target, struct stapiu_target, finder); if (!process_p) return 0; /* ignore threads */ /* ET_EXEC events are like shlib events, but with 0 relocation bases */ if (register_p) { int rc = -EINVAL; struct inode *inode = stapiu_get_task_inode(task); if (inode) { rc = stapiu_change_plus(target, task, 0, TASK_SIZE, 0, 0, inode); stapiu_change_semaphore_plus(target, task, 0, TASK_SIZE); } return rc; } else return stapiu_change_minus(target, task, 0, TASK_SIZE); } /* The task_finder_mmap_callback */ static int stapiu_mmap_found(struct stap_task_finder_target *tf_target, struct task_struct *task, char *path, struct dentry *dentry, unsigned long addr, unsigned long length, unsigned long offset, unsigned long vm_flags) { int rc = 0; struct stapiu_target *target = container_of(tf_target, struct stapiu_target, finder); /* Sanity check that the inodes match (if the target's inode * is set). Doesn't guarantee safety, but it's a start. If * the target's inode isn't set, this is the first time we've * seen this target. */ if (target->inode && dentry->d_inode != target->inode) return 0; /* The file path must match too. */ if (!path || strcmp (path, target->filename)) return 0; /* 1 - shared libraries' executable segments load from offset 0 * - ld.so convention offset != 0 is now allowed * so stap_uprobe_change_plus can set a semaphore, * i.e. a static extern, in a shared object * 2 - the shared library we're interested in * 3 - mapping should be executable or writeable (for * semaphore in .so) * NB: or both, on kernels that lack noexec mapping */ /* Check non-writable, executable sections for probes. */ if ((vm_flags & VM_EXEC) && !(vm_flags & VM_WRITE)) rc = stapiu_change_plus(target, task, addr, length, offset, vm_flags, dentry->d_inode); /* Check writeable sections for semaphores. * NB: They may have also been executable for the check above, * if we're running a kernel that lacks noexec mappings. * So long as there's no error (rc == 0), we need to look * for semaphores too. */ if ((rc == 0) && (vm_flags & VM_WRITE)) rc = stapiu_change_semaphore_plus(target, task, addr, length); return rc; } /* The task_finder_munmap_callback */ static int stapiu_munmap_found(struct stap_task_finder_target *tf_target, struct task_struct *task, unsigned long addr, unsigned long length) { struct stapiu_target *target = container_of(tf_target, struct stapiu_target, finder); return stapiu_change_minus(target, task, addr, length); } /* The task_finder_callback we use for ET_DYN targets. * This just forces an unmap of everything as the process exits. (PR11151) */ static int stapiu_process_munmap(struct stap_task_finder_target *tf_target, struct task_struct *task, int register_p, int process_p) { struct stapiu_target *target = container_of(tf_target, struct stapiu_target, finder); if (!process_p) return 0; /* ignore threads */ /* Covering 0->TASK_SIZE means "unmap everything" */ if (!register_p) return stapiu_change_minus(target, task, 0, TASK_SIZE); return 0; } #endif /* _UPROBES_INODE_C_ */