Commit 647c42df authored by Oleg Nesterov's avatar Oleg Nesterov
Browse files

uprobes: Kill uprobes_state->count 



uprobes_state->count is only needed to avoid the slow path in
uprobe_pre_sstep_notifier(). It is also checked in uprobe_munmap()
but ironically its only goal to decrement this counter. However,
it is very broken. Just some examples:

- uprobe_mmap() can race with uprobe_unregister() and wrongly
  increment the counter if it hits the non-uprobe "int3". Note
  that install_breakpoint() checks ->consumers first and returns
  -EEXIST if it is NULL.

  "atomic_sub() if error" in uprobe_mmap() looks obviously wrong
  too.

- uprobe_munmap() can race with uprobe_register() and wrongly
  decrement the counter by the same reason.

- Suppose an appication tries to increase the mmapped area via
  sys_mremap(). vma_adjust() does uprobe_munmap(whole_vma) first,
  this can nullify the counter temporarily and race with another
  thread which can hit the bp, the application will be killed by
  SIGTRAP.

- Suppose an application mmaps 2 consecutive areas in the same file
  and one (or both) of these areas has uprobes. In the likely case
  mmap_region()->vma_merge() suceeds. Like above, this leads to
  uprobe_munmap/uprobe_mmap from vma_merge()->vma_adjust() but then
  mmap_region() does another uprobe_mmap(resulting_vma) and doubles
  the counter.

This patch only removes this counter and fixes the compile errors,
then we will try to cleanup the changed code and add something else
instead.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
parent 8bd87445

include/linux/uprobes.h

+1 −1
Original line number Diff line number Diff line
@@ -99,8 +99,8 @@ struct xol_area { 


struct uprobes_state {

	struct xol_area		*xol_area;

	atomic_t		count;

};



extern int __weak set_swbp(struct arch_uprobe *aup, struct mm_struct *mm, unsigned long vaddr);

extern int __weak set_orig_insn(struct arch_uprobe *aup, struct mm_struct *mm,  unsigned long vaddr, bool verify);

extern bool __weak is_swbp_insn(uprobe_opcode_t *insn);

kernel/events/uprobes.c

+2 −36
Original line number Diff line number Diff line
@@ -678,18 +678,7 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, 
		uprobe->flags |= UPROBE_COPY_INSN;

	}



	/*

	 * Ideally, should be updating the probe count after the breakpoint

	 * has been successfully inserted. However a thread could hit the

	 * breakpoint we just inserted even before the probe count is

	 * incremented. If this is the first breakpoint placed, breakpoint

	 * notifier might ignore uprobes and pass the trap to the thread.

	 * Hence increment before and decrement on failure.

	 */

	atomic_inc(&mm->uprobes_state.count);

	ret = set_swbp(&uprobe->arch, mm, vaddr);

	if (ret)

		atomic_dec(&mm->uprobes_state.count);



	return ret;

}
@@ -697,8 +686,7 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, 
static void

remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vaddr)

{

	if (!set_orig_insn(&uprobe->arch, mm, vaddr, true))

		atomic_dec(&mm->uprobes_state.count);

	set_orig_insn(&uprobe->arch, mm, vaddr, true);

}



/*
@@ -1051,13 +1039,6 @@ int uprobe_mmap(struct vm_area_struct *vma) 


				if (!is_swbp_at_addr(vma->vm_mm, vaddr))

					continue;



				/*

				 * Unable to insert a breakpoint, but

				 * breakpoint lies underneath. Increment the

				 * probe count.

				 */

				atomic_inc(&vma->vm_mm->uprobes_state.count);

			}



			if (!ret)
@@ -1068,9 +1049,6 @@ int uprobe_mmap(struct vm_area_struct *vma) 


	mutex_unlock(uprobes_mmap_hash(inode));



	if (ret)

		atomic_sub(count, &vma->vm_mm->uprobes_state.count);



	return ret;

}
@@ -1089,9 +1067,6 @@ void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned lon 
	if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */

		return;



	if (!atomic_read(&vma->vm_mm->uprobes_state.count))

		return;



	inode = vma->vm_file->f_mapping->host;

	if (!inode)

		return;
@@ -1100,13 +1075,6 @@ void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned lon 
	build_probe_list(inode, vma, start, end, &tmp_list);



	list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {

		unsigned long vaddr = offset_to_vaddr(vma, uprobe->offset);

		/*

		 * An unregister could have removed the probe before

		 * unmap. So check before we decrement the count.

		 */

		if (is_swbp_at_addr(vma->vm_mm, vaddr) == 1)

			atomic_dec(&vma->vm_mm->uprobes_state.count);

		put_uprobe(uprobe);

	}

	mutex_unlock(uprobes_mmap_hash(inode));
@@ -1217,7 +1185,6 @@ void uprobe_clear_state(struct mm_struct *mm) 
void uprobe_reset_state(struct mm_struct *mm)

{

	mm->uprobes_state.xol_area = NULL;

	atomic_set(&mm->uprobes_state.count, 0);

}



/*
@@ -1585,8 +1552,7 @@ int uprobe_pre_sstep_notifier(struct pt_regs *regs) 
{

	struct uprobe_task *utask;



	if (!current->mm || !atomic_read(&current->mm->uprobes_state.count))

		/* task is currently not uprobed */

	if (!current->mm)

		return 0;



	utask = current->utask;

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