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Commit da1816b1 authored by Oleg Nesterov's avatar Oleg Nesterov
Browse files

uprobes: Teach handler_chain() to filter out the probed task 



Currrently the are 2 problems with pre-filtering:

1. It is not possible to add/remove a task (mm) after uprobe_register()

2. A forked child inherits all breakpoints and uprobe_consumer can not
   control this.

This patch does the first step to improve the filtering. handler_chain()
removes the breakpoints installed by this uprobe from current->mm if all
handlers return UPROBE_HANDLER_REMOVE.

Note that handler_chain() relies on ->register_rwsem to avoid the race
with uprobe_register/unregister which can add/del a consumer, or even
remove and then insert the new uprobe at the same address.

Perhaps we will add uprobe_apply_mm(uprobe, mm, is_register) and teach
copy_mm() to do filter(UPROBE_FILTER_FORK), but I think this change makes
sense anyway.

Note: instead of checking the retcode from uc->handler, we could add
uc->filter(UPROBE_FILTER_BPHIT). But I think this is not optimal to
call 2 hooks in a row. This buys nothing, and if handler/filter do
something nontrivial they will probably do the same work twice.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
parent 8a7f2fa0

include/linux/uprobes.h

+3 −0
Original line number Diff line number Diff line
@@ -35,6 +35,9 @@ struct inode; 
# include <asm/uprobes.h>

#endif



#define UPROBE_HANDLER_REMOVE		1

#define UPROBE_HANDLER_MASK		1



enum uprobe_filter_ctx {

	UPROBE_FILTER_REGISTER,

	UPROBE_FILTER_UNREGISTER,

kernel/events/uprobes.c

+48 −10
Original line number Diff line number Diff line
@@ -440,16 +440,6 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset) 
	return uprobe;

}



static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)

{

	struct uprobe_consumer *uc;



	down_read(&uprobe->register_rwsem);

	for (uc = uprobe->consumers; uc; uc = uc->next)

		uc->handler(uc, regs);

	up_read(&uprobe->register_rwsem);

}



static void consumer_add(struct uprobe *uprobe, struct uprobe_consumer *uc)

{

	down_write(&uprobe->consumer_rwsem);
@@ -882,6 +872,33 @@ void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consume 
	put_uprobe(uprobe);

}



static int unapply_uprobe(struct uprobe *uprobe, struct mm_struct *mm)

{

	struct vm_area_struct *vma;

	int err = 0;



	down_read(&mm->mmap_sem);

	for (vma = mm->mmap; vma; vma = vma->vm_next) {

		unsigned long vaddr;

		loff_t offset;



		if (!valid_vma(vma, false) ||

		    vma->vm_file->f_mapping->host != uprobe->inode)

			continue;



		offset = (loff_t)vma->vm_pgoff << PAGE_SHIFT;

		if (uprobe->offset <  offset ||

		    uprobe->offset >= offset + vma->vm_end - vma->vm_start)

			continue;



		vaddr = offset_to_vaddr(vma, uprobe->offset);

		err |= remove_breakpoint(uprobe, mm, vaddr);

	}

	up_read(&mm->mmap_sem);



	return err;

}



static struct rb_node *

find_node_in_range(struct inode *inode, loff_t min, loff_t max)

{
@@ -1435,6 +1452,27 @@ static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp) 
	return uprobe;

}



static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)

{

	struct uprobe_consumer *uc;

	int remove = UPROBE_HANDLER_REMOVE;



	down_read(&uprobe->register_rwsem);

	for (uc = uprobe->consumers; uc; uc = uc->next) {

		int rc = uc->handler(uc, regs);



		WARN(rc & ~UPROBE_HANDLER_MASK,

			"bad rc=0x%x from %pf()\n", rc, uc->handler);

		remove &= rc;

	}



	if (remove && uprobe->consumers) {

		WARN_ON(!uprobe_is_active(uprobe));

		unapply_uprobe(uprobe, current->mm);

	}

	up_read(&uprobe->register_rwsem);

}



/*

 * Run handler and ask thread to singlestep.

 * Ensure all non-fatal signals cannot interrupt thread while it singlesteps.