uprobes: Introduce MMF_RECALC_UPROBES

Add the new MMF_RECALC_UPROBES flag, it means that MMF_HAS_UPROBES can be false positive after remove_breakpoint() or uprobe_munmap(). It is also set by uprobe_dup_mmap(), this is not optimal but simple. We could add the new hook, uprobe_dup_vma(), to set MMF_HAS_UPROBES only if the new mm actually has uprobes, but I don't think this makes sense. The next patch will use this flag to clear MMF_HAS_UPROBES. Signed-off-by: Oleg Nesterov <[email protected]> Acked-by: Srikar Dronamraju <[email protected]>
kevsmith · Sep 15, 2012 · 9f68f67 · 9f68f67
1 parent 6f47caa
commit 9f68f67
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Showing 2 changed files with 37 additions and 5 deletions.
diff --git a/include/linux/sched.h b/include/linux/sched.h
@@ -446,7 +446,8 @@ extern int get_dumpable(struct mm_struct *mm);
 #define MMF_VM_HUGEPAGE		17	/* set when VM_HUGEPAGE is set on vma */
 #define MMF_EXE_FILE_CHANGED	18	/* see prctl_set_mm_exe_file() */
 
-#define MMF_HAS_UPROBES		19	/* might have uprobes */
+#define MMF_HAS_UPROBES		19	/* has uprobes */
+#define MMF_RECALC_UPROBES	20	/* MMF_HAS_UPROBES can be wrong */
 
 #define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
 

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
@@ -684,7 +684,9 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
 		set_bit(MMF_HAS_UPROBES, &mm->flags);
 
 	ret = set_swbp(&uprobe->arch, mm, vaddr);
-	if (ret && first_uprobe)
+	if (!ret)
+		clear_bit(MMF_RECALC_UPROBES, &mm->flags);
+	else if (first_uprobe)
 		clear_bit(MMF_HAS_UPROBES, &mm->flags);
 
 	return ret;
@@ -693,6 +695,11 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
 static void
 remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vaddr)
 {
+	/* can happen if uprobe_register() fails */
+	if (!test_bit(MMF_HAS_UPROBES, &mm->flags))
+		return;
+
+	set_bit(MMF_RECALC_UPROBES, &mm->flags);
 	set_orig_insn(&uprobe->arch, mm, vaddr);
 }
 
@@ -1026,6 +1033,25 @@ int uprobe_mmap(struct vm_area_struct *vma)
 	return 0;
 }
 
+static bool
+vma_has_uprobes(struct vm_area_struct *vma, unsigned long start, unsigned long end)
+{
+	loff_t min, max;
+	struct inode *inode;
+	struct rb_node *n;
+
+	inode = vma->vm_file->f_mapping->host;
+
+	min = vaddr_to_offset(vma, start);
+	max = min + (end - start) - 1;
+
+	spin_lock(&uprobes_treelock);
+	n = find_node_in_range(inode, min, max);
+	spin_unlock(&uprobes_treelock);
+
+	return !!n;
+}
+
 /*
  * Called in context of a munmap of a vma.
  */
@@ -1037,10 +1063,12 @@ 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 (!test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags))
+	if (!test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags) ||
+	     test_bit(MMF_RECALC_UPROBES, &vma->vm_mm->flags))
 		return;
 
-	/* TODO: unmapping uprobe(s) will need more work */
+	if (vma_has_uprobes(vma, start, end))
+		set_bit(MMF_RECALC_UPROBES, &vma->vm_mm->flags);
 }
 
 /* Slot allocation for XOL */
@@ -1146,8 +1174,11 @@ void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm)
 {
 	newmm->uprobes_state.xol_area = NULL;
 
-	if (test_bit(MMF_HAS_UPROBES, &oldmm->flags))
+	if (test_bit(MMF_HAS_UPROBES, &oldmm->flags)) {
 		set_bit(MMF_HAS_UPROBES, &newmm->flags);
+		/* unconditionally, dup_mmap() skips VM_DONTCOPY vmas */
+		set_bit(MMF_RECALC_UPROBES, &newmm->flags);
+	}
 }
 
 /*