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uprobes: Kill uprobes_state->count

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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: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
This commit is contained in:
Oleg Nesterov 2012-08-06 13:15:09 +02:00
parent 8bd874456e
commit 647c42dfd4
2 changed files with 3 additions and 37 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/uprobes.h
View File

@ -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);

38
kernel/events/uprobes.c
View File

@ -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;