Commit f8ac4ec9 authored by Oleg Nesterov's avatar Oleg Nesterov
Browse files

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: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
parent 78f74116

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -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 {

include/linux/uprobes.h

+5 −0
Original line number Diff line number Diff line
@@ -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)

{

}

kernel/events/uprobes.c

+21 −1
Original line number Diff line number Diff line
@@ -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;

kernel/fork.c

+1 −0
Original line number Diff line number Diff line
@@ -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:

	 */

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