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Date: Thu, 10 Jan 2013 11:05:01 +0530
From: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
Ananth N Mavinakayanahalli <ananth@...ibm.com>,
Anton Arapov <anton@...hat.com>,
Frank Eigler <fche@...hat.com>,
Josh Stone <jistone@...hat.com>,
"Suzuki K. Poulose" <suzuki@...ibm.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] uprobes: Teach handler_chain() to filter out the
probed task
* Oleg Nesterov <oleg@...hat.com> [2012-12-29 18:36:14]:
> 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: Oleg Nesterov <oleg@...hat.com>
Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> ---
> include/linux/uprobes.h | 3 ++
> kernel/events/uprobes.c | 58 ++++++++++++++++++++++++++++++++++++++--------
> 2 files changed, 51 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index c2df693..95d0002 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -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,
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index e2ebb6f..59b6e97 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -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.
> --
> 1.5.5.1
>
>
--
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