2 * User-space Probes (UProbes)
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18 * Copyright (C) IBM Corporation, 2008-2012
22 * Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
25 #include <linux/kernel.h>
26 #include <linux/highmem.h>
27 #include <linux/pagemap.h> /* read_mapping_page */
28 #include <linux/slab.h>
29 #include <linux/sched.h>
30 #include <linux/rmap.h> /* anon_vma_prepare */
31 #include <linux/mmu_notifier.h> /* set_pte_at_notify */
32 #include <linux/swap.h> /* try_to_free_swap */
34 #include <linux/uprobes.h>
36 static struct rb_root uprobes_tree = RB_ROOT;
38 static DEFINE_SPINLOCK(uprobes_treelock); /* serialize rbtree access */
40 #define UPROBES_HASH_SZ 13
42 /* serialize (un)register */
43 static struct mutex uprobes_mutex[UPROBES_HASH_SZ];
45 #define uprobes_hash(v) (&uprobes_mutex[((unsigned long)(v)) % UPROBES_HASH_SZ])
47 /* serialize uprobe->pending_list */
48 static struct mutex uprobes_mmap_mutex[UPROBES_HASH_SZ];
49 #define uprobes_mmap_hash(v) (&uprobes_mmap_mutex[((unsigned long)(v)) % UPROBES_HASH_SZ])
52 * uprobe_events allows us to skip the uprobe_mmap if there are no uprobe
53 * events active at this time. Probably a fine grained per inode count is
56 static atomic_t uprobe_events = ATOMIC_INIT(0);
59 * Maintain a temporary per vma info that can be used to search if a vma
60 * has already been handled. This structure is introduced since extending
61 * vm_area_struct wasnt recommended.
64 struct list_head probe_list;
70 struct rb_node rb_node; /* node in the rb tree */
72 struct rw_semaphore consumer_rwsem;
73 struct list_head pending_list;
74 struct uprobe_consumer *consumers;
75 struct inode *inode; /* Also hold a ref to inode */
78 struct arch_uprobe arch;
82 * valid_vma: Verify if the specified vma is an executable vma
83 * Relax restrictions while unregistering: vm_flags might have
84 * changed after breakpoint was inserted.
85 * - is_register: indicates if we are in register context.
86 * - Return 1 if the specified virtual address is in an
89 static bool valid_vma(struct vm_area_struct *vma, bool is_register)
97 if ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) == (VM_READ|VM_EXEC))
103 static loff_t vma_address(struct vm_area_struct *vma, loff_t offset)
107 vaddr = vma->vm_start + offset;
108 vaddr -= vma->vm_pgoff << PAGE_SHIFT;
114 * __replace_page - replace page in vma by new page.
115 * based on replace_page in mm/ksm.c
117 * @vma: vma that holds the pte pointing to page
118 * @page: the cowed page we are replacing by kpage
119 * @kpage: the modified page we replace page by
121 * Returns 0 on success, -EFAULT on failure.
123 static int __replace_page(struct vm_area_struct *vma, struct page *page, struct page *kpage)
125 struct mm_struct *mm = vma->vm_mm;
134 addr = page_address_in_vma(page, vma);
138 pgd = pgd_offset(mm, addr);
139 if (!pgd_present(*pgd))
142 pud = pud_offset(pgd, addr);
143 if (!pud_present(*pud))
146 pmd = pmd_offset(pud, addr);
147 if (!pmd_present(*pmd))
150 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
155 page_add_new_anon_rmap(kpage, vma, addr);
157 flush_cache_page(vma, addr, pte_pfn(*ptep));
158 ptep_clear_flush(vma, addr, ptep);
159 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
161 page_remove_rmap(page);
162 if (!page_mapped(page))
163 try_to_free_swap(page);
165 pte_unmap_unlock(ptep, ptl);
173 * is_swbp_insn - check if instruction is breakpoint instruction.
174 * @insn: instruction to be checked.
175 * Default implementation of is_swbp_insn
176 * Returns true if @insn is a breakpoint instruction.
178 bool __weak is_swbp_insn(uprobe_opcode_t *insn)
180 return *insn == UPROBE_SWBP_INSN;
185 * Expect the breakpoint instruction to be the smallest size instruction for
186 * the architecture. If an arch has variable length instruction and the
187 * breakpoint instruction is not of the smallest length instruction
188 * supported by that architecture then we need to modify read_opcode /
189 * write_opcode accordingly. This would never be a problem for archs that
190 * have fixed length instructions.
194 * write_opcode - write the opcode at a given virtual address.
195 * @auprobe: arch breakpointing information.
196 * @mm: the probed process address space.
197 * @vaddr: the virtual address to store the opcode.
198 * @opcode: opcode to be written at @vaddr.
200 * Called with mm->mmap_sem held (for read and with a reference to
203 * For mm @mm, write the opcode at @vaddr.
204 * Return 0 (success) or a negative errno.
206 static int write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
207 unsigned long vaddr, uprobe_opcode_t opcode)
209 struct page *old_page, *new_page;
210 struct address_space *mapping;
211 void *vaddr_old, *vaddr_new;
212 struct vm_area_struct *vma;
213 struct uprobe *uprobe;
217 /* Read the page with vaddr into memory */
218 ret = get_user_pages(NULL, mm, vaddr, 1, 0, 0, &old_page, &vma);
225 * We are interested in text pages only. Our pages of interest
226 * should be mapped for read and execute only. We desist from
227 * adding probes in write mapped pages since the breakpoints
228 * might end up in the file copy.
230 if (!valid_vma(vma, is_swbp_insn(&opcode)))
233 uprobe = container_of(auprobe, struct uprobe, arch);
234 mapping = uprobe->inode->i_mapping;
235 if (mapping != vma->vm_file->f_mapping)
238 addr = vma_address(vma, uprobe->offset);
239 if (vaddr != (unsigned long)addr)
243 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr);
247 __SetPageUptodate(new_page);
250 * lock page will serialize against do_wp_page()'s
251 * PageAnon() handling
254 /* copy the page now that we've got it stable */
255 vaddr_old = kmap_atomic(old_page);
256 vaddr_new = kmap_atomic(new_page);
258 memcpy(vaddr_new, vaddr_old, PAGE_SIZE);
260 /* poke the new insn in, ASSUMES we don't cross page boundary */
262 BUG_ON(vaddr + UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
263 memcpy(vaddr_new + vaddr, &opcode, UPROBE_SWBP_INSN_SIZE);
265 kunmap_atomic(vaddr_new);
266 kunmap_atomic(vaddr_old);
268 ret = anon_vma_prepare(vma);
273 ret = __replace_page(vma, old_page, new_page);
274 unlock_page(new_page);
277 unlock_page(old_page);
278 page_cache_release(new_page);
287 * read_opcode - read the opcode at a given virtual address.
288 * @mm: the probed process address space.
289 * @vaddr: the virtual address to read the opcode.
290 * @opcode: location to store the read opcode.
292 * Called with mm->mmap_sem held (for read and with a reference to
295 * For mm @mm, read the opcode at @vaddr and store it in @opcode.
296 * Return 0 (success) or a negative errno.
298 static int read_opcode(struct mm_struct *mm, unsigned long vaddr, uprobe_opcode_t *opcode)
304 ret = get_user_pages(NULL, mm, vaddr, 1, 0, 0, &page, NULL);
309 vaddr_new = kmap_atomic(page);
311 memcpy(opcode, vaddr_new + vaddr, UPROBE_SWBP_INSN_SIZE);
312 kunmap_atomic(vaddr_new);
320 static int is_swbp_at_addr(struct mm_struct *mm, unsigned long vaddr)
322 uprobe_opcode_t opcode;
325 result = read_opcode(mm, vaddr, &opcode);
329 if (is_swbp_insn(&opcode))
336 * set_swbp - store breakpoint at a given address.
337 * @auprobe: arch specific probepoint information.
338 * @mm: the probed process address space.
339 * @vaddr: the virtual address to insert the opcode.
341 * For mm @mm, store the breakpoint instruction at @vaddr.
342 * Return 0 (success) or a negative errno.
344 int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
348 result = is_swbp_at_addr(mm, vaddr);
355 return write_opcode(auprobe, mm, vaddr, UPROBE_SWBP_INSN);
359 * set_orig_insn - Restore the original instruction.
360 * @mm: the probed process address space.
361 * @auprobe: arch specific probepoint information.
362 * @vaddr: the virtual address to insert the opcode.
363 * @verify: if true, verify existance of breakpoint instruction.
365 * For mm @mm, restore the original opcode (opcode) at @vaddr.
366 * Return 0 (success) or a negative errno.
369 set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr, bool verify)
374 result = is_swbp_at_addr(mm, vaddr);
381 return write_opcode(auprobe, mm, vaddr, *(uprobe_opcode_t *)auprobe->insn);
384 static int match_uprobe(struct uprobe *l, struct uprobe *r)
386 if (l->inode < r->inode)
389 if (l->inode > r->inode)
392 if (l->offset < r->offset)
395 if (l->offset > r->offset)
401 static struct uprobe *__find_uprobe(struct inode *inode, loff_t offset)
403 struct uprobe u = { .inode = inode, .offset = offset };
404 struct rb_node *n = uprobes_tree.rb_node;
405 struct uprobe *uprobe;
409 uprobe = rb_entry(n, struct uprobe, rb_node);
410 match = match_uprobe(&u, uprobe);
412 atomic_inc(&uprobe->ref);
425 * Find a uprobe corresponding to a given inode:offset
426 * Acquires uprobes_treelock
428 static struct uprobe *find_uprobe(struct inode *inode, loff_t offset)
430 struct uprobe *uprobe;
433 spin_lock_irqsave(&uprobes_treelock, flags);
434 uprobe = __find_uprobe(inode, offset);
435 spin_unlock_irqrestore(&uprobes_treelock, flags);
440 static struct uprobe *__insert_uprobe(struct uprobe *uprobe)
442 struct rb_node **p = &uprobes_tree.rb_node;
443 struct rb_node *parent = NULL;
449 u = rb_entry(parent, struct uprobe, rb_node);
450 match = match_uprobe(uprobe, u);
457 p = &parent->rb_left;
459 p = &parent->rb_right;
464 rb_link_node(&uprobe->rb_node, parent, p);
465 rb_insert_color(&uprobe->rb_node, &uprobes_tree);
466 /* get access + creation ref */
467 atomic_set(&uprobe->ref, 2);
473 * Acquire uprobes_treelock.
474 * Matching uprobe already exists in rbtree;
475 * increment (access refcount) and return the matching uprobe.
477 * No matching uprobe; insert the uprobe in rb_tree;
478 * get a double refcount (access + creation) and return NULL.
480 static struct uprobe *insert_uprobe(struct uprobe *uprobe)
485 spin_lock_irqsave(&uprobes_treelock, flags);
486 u = __insert_uprobe(uprobe);
487 spin_unlock_irqrestore(&uprobes_treelock, flags);
492 static void put_uprobe(struct uprobe *uprobe)
494 if (atomic_dec_and_test(&uprobe->ref))
498 static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
500 struct uprobe *uprobe, *cur_uprobe;
502 uprobe = kzalloc(sizeof(struct uprobe), GFP_KERNEL);
506 uprobe->inode = igrab(inode);
507 uprobe->offset = offset;
508 init_rwsem(&uprobe->consumer_rwsem);
509 INIT_LIST_HEAD(&uprobe->pending_list);
511 /* add to uprobes_tree, sorted on inode:offset */
512 cur_uprobe = insert_uprobe(uprobe);
514 /* a uprobe exists for this inode:offset combination */
520 atomic_inc(&uprobe_events);
526 /* Returns the previous consumer */
527 static struct uprobe_consumer *
528 consumer_add(struct uprobe *uprobe, struct uprobe_consumer *uc)
530 down_write(&uprobe->consumer_rwsem);
531 uc->next = uprobe->consumers;
532 uprobe->consumers = uc;
533 up_write(&uprobe->consumer_rwsem);
539 * For uprobe @uprobe, delete the consumer @uc.
540 * Return true if the @uc is deleted successfully
543 static bool consumer_del(struct uprobe *uprobe, struct uprobe_consumer *uc)
545 struct uprobe_consumer **con;
548 down_write(&uprobe->consumer_rwsem);
549 for (con = &uprobe->consumers; *con; con = &(*con)->next) {
556 up_write(&uprobe->consumer_rwsem);
562 __copy_insn(struct address_space *mapping, struct vm_area_struct *vma, char *insn,
563 unsigned long nbytes, unsigned long offset)
565 struct file *filp = vma->vm_file;
574 idx = (unsigned long)(offset >> PAGE_CACHE_SHIFT);
575 off1 = offset &= ~PAGE_MASK;
578 * Ensure that the page that has the original instruction is
579 * populated and in page-cache.
581 page = read_mapping_page(mapping, idx, filp);
583 return PTR_ERR(page);
585 vaddr = kmap_atomic(page);
586 memcpy(insn, vaddr + off1, nbytes);
587 kunmap_atomic(vaddr);
588 page_cache_release(page);
594 copy_insn(struct uprobe *uprobe, struct vm_area_struct *vma, unsigned long addr)
596 struct address_space *mapping;
597 unsigned long nbytes;
601 nbytes = PAGE_SIZE - addr;
602 mapping = uprobe->inode->i_mapping;
604 /* Instruction at end of binary; copy only available bytes */
605 if (uprobe->offset + MAX_UINSN_BYTES > uprobe->inode->i_size)
606 bytes = uprobe->inode->i_size - uprobe->offset;
608 bytes = MAX_UINSN_BYTES;
610 /* Instruction at the page-boundary; copy bytes in second page */
611 if (nbytes < bytes) {
612 if (__copy_insn(mapping, vma, uprobe->arch.insn + nbytes,
613 bytes - nbytes, uprobe->offset + nbytes))
618 return __copy_insn(mapping, vma, uprobe->arch.insn, bytes, uprobe->offset);
622 install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
623 struct vm_area_struct *vma, loff_t vaddr)
629 * If probe is being deleted, unregister thread could be done with
630 * the vma-rmap-walk through. Adding a probe now can be fatal since
631 * nobody will be able to cleanup. Also we could be from fork or
632 * mremap path, where the probe might have already been inserted.
633 * Hence behave as if probe already existed.
635 if (!uprobe->consumers)
638 addr = (unsigned long)vaddr;
640 if (!(uprobe->flags & UPROBE_COPY_INSN)) {
641 ret = copy_insn(uprobe, vma, addr);
645 if (is_swbp_insn((uprobe_opcode_t *)uprobe->arch.insn))
648 ret = arch_uprobes_analyze_insn(&uprobe->arch, mm);
652 uprobe->flags |= UPROBE_COPY_INSN;
654 ret = set_swbp(&uprobe->arch, mm, addr);
660 remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, loff_t vaddr)
662 set_orig_insn(&uprobe->arch, mm, (unsigned long)vaddr, true);
665 static void delete_uprobe(struct uprobe *uprobe)
669 spin_lock_irqsave(&uprobes_treelock, flags);
670 rb_erase(&uprobe->rb_node, &uprobes_tree);
671 spin_unlock_irqrestore(&uprobes_treelock, flags);
674 atomic_dec(&uprobe_events);
677 static struct vma_info *
678 __find_next_vma_info(struct address_space *mapping, struct list_head *head,
679 struct vma_info *vi, loff_t offset, bool is_register)
681 struct prio_tree_iter iter;
682 struct vm_area_struct *vma;
683 struct vma_info *tmpvi;
688 pgoff = offset >> PAGE_SHIFT;
690 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
691 if (!valid_vma(vma, is_register))
695 vaddr = vma_address(vma, offset);
697 list_for_each_entry(tmpvi, head, probe_list) {
698 if (tmpvi->mm == vma->vm_mm && tmpvi->vaddr == vaddr) {
705 * Another vma needs a probe to be installed. However skip
706 * installing the probe if the vma is about to be unlinked.
708 if (!existing_vma && atomic_inc_not_zero(&vma->vm_mm->mm_users)) {
711 list_add(&vi->probe_list, head);
721 * Iterate in the rmap prio tree and find a vma where a probe has not
724 static struct vma_info *
725 find_next_vma_info(struct address_space *mapping, struct list_head *head,
726 loff_t offset, bool is_register)
728 struct vma_info *vi, *retvi;
730 vi = kzalloc(sizeof(struct vma_info), GFP_KERNEL);
732 return ERR_PTR(-ENOMEM);
734 mutex_lock(&mapping->i_mmap_mutex);
735 retvi = __find_next_vma_info(mapping, head, vi, offset, is_register);
736 mutex_unlock(&mapping->i_mmap_mutex);
744 static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
746 struct list_head try_list;
747 struct vm_area_struct *vma;
748 struct address_space *mapping;
749 struct vma_info *vi, *tmpvi;
750 struct mm_struct *mm;
754 mapping = uprobe->inode->i_mapping;
755 INIT_LIST_HEAD(&try_list);
760 vi = find_next_vma_info(mapping, &try_list, uprobe->offset, is_register);
770 down_read(&mm->mmap_sem);
771 vma = find_vma(mm, (unsigned long)vi->vaddr);
772 if (!vma || !valid_vma(vma, is_register)) {
773 list_del(&vi->probe_list);
775 up_read(&mm->mmap_sem);
779 vaddr = vma_address(vma, uprobe->offset);
780 if (vma->vm_file->f_mapping->host != uprobe->inode ||
781 vaddr != vi->vaddr) {
782 list_del(&vi->probe_list);
784 up_read(&mm->mmap_sem);
790 ret = install_breakpoint(uprobe, mm, vma, vi->vaddr);
792 remove_breakpoint(uprobe, mm, vi->vaddr);
794 up_read(&mm->mmap_sem);
797 if (ret && ret == -EEXIST)
804 list_for_each_entry_safe(vi, tmpvi, &try_list, probe_list) {
805 list_del(&vi->probe_list);
812 static int __uprobe_register(struct uprobe *uprobe)
814 return register_for_each_vma(uprobe, true);
817 static void __uprobe_unregister(struct uprobe *uprobe)
819 if (!register_for_each_vma(uprobe, false))
820 delete_uprobe(uprobe);
822 /* TODO : cant unregister? schedule a worker thread */
826 * uprobe_register - register a probe
827 * @inode: the file in which the probe has to be placed.
828 * @offset: offset from the start of the file.
829 * @uc: information on howto handle the probe..
831 * Apart from the access refcount, uprobe_register() takes a creation
832 * refcount (thro alloc_uprobe) if and only if this @uprobe is getting
833 * inserted into the rbtree (i.e first consumer for a @inode:@offset
834 * tuple). Creation refcount stops uprobe_unregister from freeing the
835 * @uprobe even before the register operation is complete. Creation
836 * refcount is released when the last @uc for the @uprobe
839 * Return errno if it cannot successully install probes
840 * else return 0 (success)
842 int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *uc)
844 struct uprobe *uprobe;
847 if (!inode || !uc || uc->next)
850 if (offset > i_size_read(inode))
854 mutex_lock(uprobes_hash(inode));
855 uprobe = alloc_uprobe(inode, offset);
857 if (uprobe && !consumer_add(uprobe, uc)) {
858 ret = __uprobe_register(uprobe);
860 uprobe->consumers = NULL;
861 __uprobe_unregister(uprobe);
863 uprobe->flags |= UPROBE_RUN_HANDLER;
867 mutex_unlock(uprobes_hash(inode));
874 * uprobe_unregister - unregister a already registered probe.
875 * @inode: the file in which the probe has to be removed.
876 * @offset: offset from the start of the file.
877 * @uc: identify which probe if multiple probes are colocated.
879 void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc)
881 struct uprobe *uprobe;
886 uprobe = find_uprobe(inode, offset);
890 mutex_lock(uprobes_hash(inode));
892 if (consumer_del(uprobe, uc)) {
893 if (!uprobe->consumers) {
894 __uprobe_unregister(uprobe);
895 uprobe->flags &= ~UPROBE_RUN_HANDLER;
899 mutex_unlock(uprobes_hash(inode));
905 * Of all the nodes that correspond to the given inode, return the node
906 * with the least offset.
908 static struct rb_node *find_least_offset_node(struct inode *inode)
910 struct uprobe u = { .inode = inode, .offset = 0};
911 struct rb_node *n = uprobes_tree.rb_node;
912 struct rb_node *close_node = NULL;
913 struct uprobe *uprobe;
917 uprobe = rb_entry(n, struct uprobe, rb_node);
918 match = match_uprobe(&u, uprobe);
920 if (uprobe->inode == inode)
936 * For a given inode, build a list of probes that need to be inserted.
938 static void build_probe_list(struct inode *inode, struct list_head *head)
940 struct uprobe *uprobe;
944 spin_lock_irqsave(&uprobes_treelock, flags);
946 n = find_least_offset_node(inode);
948 for (; n; n = rb_next(n)) {
949 uprobe = rb_entry(n, struct uprobe, rb_node);
950 if (uprobe->inode != inode)
953 list_add(&uprobe->pending_list, head);
954 atomic_inc(&uprobe->ref);
957 spin_unlock_irqrestore(&uprobes_treelock, flags);
961 * Called from mmap_region.
962 * called with mm->mmap_sem acquired.
964 * Return -ve no if we fail to insert probes and we cannot
966 * Return 0 otherwise. i.e:
968 * - successful insertion of probes
969 * - (or) no possible probes to be inserted.
970 * - (or) insertion of probes failed but we can bail-out.
972 int uprobe_mmap(struct vm_area_struct *vma)
974 struct list_head tmp_list;
975 struct uprobe *uprobe, *u;
979 if (!atomic_read(&uprobe_events) || !valid_vma(vma, true))
982 inode = vma->vm_file->f_mapping->host;
986 INIT_LIST_HEAD(&tmp_list);
987 mutex_lock(uprobes_mmap_hash(inode));
988 build_probe_list(inode, &tmp_list);
992 list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {
995 list_del(&uprobe->pending_list);
997 vaddr = vma_address(vma, uprobe->offset);
998 if (vaddr >= vma->vm_start && vaddr < vma->vm_end) {
999 ret = install_breakpoint(uprobe, vma->vm_mm, vma, vaddr);
1000 /* Ignore double add: */
1008 mutex_unlock(uprobes_mmap_hash(inode));
1013 static int __init init_uprobes(void)
1017 for (i = 0; i < UPROBES_HASH_SZ; i++) {
1018 mutex_init(&uprobes_mutex[i]);
1019 mutex_init(&uprobes_mmap_mutex[i]);
1024 static void __exit exit_uprobes(void)
1028 module_init(init_uprobes);
1029 module_exit(exit_uprobes);