uprobes: Introduce MMF_HAS_UPROBES

Add the new MMF_HAS_UPROBES flag. It is set by install_breakpoint()
and it is copied by dup_mmap(), uprobe_pre_sstep_notifier() checks
it to avoid the slow path if the task was never probed. Perhaps it
makes sense to check it in valid_vma(is_register => false) as well.

This needs the new dup_mmap()->uprobe_dup_mmap() hook. We can't use
uprobe_reset_state() or put MMF_HAS_UPROBES into MMF_INIT_MASK, we
need oldmm->mmap_sem to avoid the race with uprobe_register() or
mmap() from another thread.

Currently we never clear this bit, it can be false-positive after
uprobe_unregister() or uprobe_munmap() or if dup_mmap() hits the
probed VM_DONTCOPY vma. But this is fine correctness-wise and has
no effect unless the task hits the non-uprobe breakpoint.

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 b8c86648a2f95dc6f83aab668fd9a7e07f277b4e..3667c332e61de85b70e656cd54fd89b73365458b 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -446,6 +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_INIT_MASK          (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
 
 struct sighand_struct {

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 03ae547c1c3137cb3b05d9dd675354203b0c6184..4a37ab1532478dc24f45725dbf7e3293c0961b31 100644 (file)
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -108,6 +108,7 @@ extern int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_con
 extern void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc);
 extern int uprobe_mmap(struct vm_area_struct *vma);
 extern void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end);
+extern void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm);
 extern void uprobe_free_utask(struct task_struct *t);
 extern void uprobe_copy_process(struct task_struct *t);
 extern unsigned long __weak uprobe_get_swbp_addr(struct pt_regs *regs);
@@ -138,6 +139,10 @@ static inline void
 uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end)
 {
 }
+static inline void
+uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm)
+{
+}
 static inline void uprobe_notify_resume(struct pt_regs *regs)
 {
 }

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 3e2996b809be725a4b1e1b8e085555b67fcff2c5..33870b17e1dda7d6a78bedc6686f4342414ba20d 100644 (file)
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -647,6 +647,7 @@ static int
 install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
                        struct vm_area_struct *vma, unsigned long vaddr)
 {
+       bool first_uprobe;
        int ret;
 
        /*
@@ -678,7 +679,17 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
                uprobe->flags |= UPROBE_COPY_INSN;
        }
 
+       /*
+        * set MMF_HAS_UPROBES in advance for uprobe_pre_sstep_notifier(),
+        * the task can hit this breakpoint right after __replace_page().
+        */
+       first_uprobe = !test_bit(MMF_HAS_UPROBES, &mm->flags);
+       if (first_uprobe)
+               set_bit(MMF_HAS_UPROBES, &mm->flags);
+
        ret = set_swbp(&uprobe->arch, mm, vaddr);
+       if (ret && first_uprobe)
+               clear_bit(MMF_HAS_UPROBES, &mm->flags);
 
        return ret;
 }
@@ -1032,6 +1043,9 @@ 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))
+               return;
+
        /* TODO: unmapping uprobe(s) will need more work */
 }
 
@@ -1142,6 +1156,12 @@ void uprobe_reset_state(struct mm_struct *mm)
        mm->uprobes_state.xol_area = NULL;
 }
 
+void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm)
+{
+       if (test_bit(MMF_HAS_UPROBES, &oldmm->flags))
+               set_bit(MMF_HAS_UPROBES, &newmm->flags);
+}
+
 /*
  *  - search for a free slot.
  */
@@ -1507,7 +1527,7 @@ int uprobe_pre_sstep_notifier(struct pt_regs *regs)
 {
        struct uprobe_task *utask;
 
-       if (!current->mm)
+       if (!current->mm || !test_bit(MMF_HAS_UPROBES, &current->mm->flags))
                return 0;
 
        utask = current->utask;

diff --git a/kernel/fork.c b/kernel/fork.c
index 912b6f6fe5b8822a11afa60ec78c2eea6f64a380..cbb5f9fcd3e827eb445b35e198a7d809f70b144c 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -353,6 +353,7 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 
        down_write(&oldmm->mmap_sem);
        flush_cache_dup_mm(oldmm);
+       uprobe_dup_mmap(oldmm, mm);
        /*
         * Not linked in yet - no deadlock potential:
         */