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>

1 files changed, 35 insertions, 4 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index ba9f1e7c6060..9a7f08bab91f 100644
--- 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);
+        }
 }
 
 /*