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 <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3667c33..255661d 100644 (file)
--- 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
index ba9f1e7..9a7f08b 100644 (file)
--- 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);
+       }
 }
 
 /*