Re: [PATCH 2/2] uprobes: Reintroduce uprobe_consumer->filter()

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

* Oleg Nesterov <oleg@redhat.com> [2012-12-28 19:13:14]:

> Finally add uprobe_consumer->filter() and change consumer_filter()
> to actually call this method.
> 
> Note that ->filter() accepts mm_struct, not task_struct. Because:
> 
> 	1. We do not have for_each_mm_user(mm, task).
> 
> 	2. Even if we implement for_each_mm_user(), ->filter() can
> 	   use it itself.
> 
> 	3. It is not clear who will actually need this interface to
> 	   do the "nontrivial" filtering.
> 
> Another argument is "enum uprobe_filter_ctx", consumer->filter() can
> use it to figure out why/where it was called. For example, perhaps
> we can add UPROBE_FILTER_PRE_REGISTER used by build_map_info() to
> quickly "nack" the unwanted mm's. In this case consumer should know
> that it is called under ->i_mmap_mutex.
> 
> See the previous discussion at http://marc.info/?t=135214229700002
> Perhaps we should pass more arguments, vma/vaddr?
> 
> Note: this patch obviously can't help to filter out the child created
> by fork(), this will be addressed later.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> ---
>  include/linux/uprobes.h |    9 +++++++++
>  kernel/events/uprobes.c |   18 +++++++++++-------
>  2 files changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 83742b9..c2df693 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -35,8 +35,17 @@ struct inode;
>  # include <asm/uprobes.h>
>  #endif
> 
> +enum uprobe_filter_ctx {
> +	UPROBE_FILTER_REGISTER,
> +	UPROBE_FILTER_UNREGISTER,
> +	UPROBE_FILTER_MMAP,
> +};
> +
>  struct uprobe_consumer {
>  	int (*handler)(struct uprobe_consumer *self, struct pt_regs *regs);
> +	bool (*filter)(struct uprobe_consumer *self,
> +				enum uprobe_filter_ctx ctx,
> +				struct mm_struct *mm);
> 
>  	struct uprobe_consumer *next;
>  };
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 60b0a90..e2ebb6f 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -579,19 +579,21 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
>  	return ret;
>  }
> 
> -static inline bool consumer_filter(struct uprobe_consumer *uc)
> +static inline bool consumer_filter(struct uprobe_consumer *uc,
> +				   enum uprobe_filter_ctx ctx, struct mm_struct *mm)
>  {
> -	return true; /* TODO: !uc->filter || uc->filter(...) */
> +	return !uc->filter || uc->filter(uc, ctx, mm);
>  }
> 
> -static bool filter_chain(struct uprobe *uprobe)
> +static bool filter_chain(struct uprobe *uprobe,
> +			 enum uprobe_filter_ctx ctx, struct mm_struct *mm)
>  {
>  	struct uprobe_consumer *uc;
>  	bool ret = false;
> 
>  	down_read(&uprobe->consumer_rwsem);
>  	for (uc = uprobe->consumers; uc; uc = uc->next) {
> -		ret = consumer_filter(uc);
> +		ret = consumer_filter(uc, ctx, mm);
>  		if (ret)
>  			break;
>  	}
> @@ -772,10 +774,12 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
> 
>  		if (is_register) {
>  			/* consult only the "caller", new consumer. */
> -			if (consumer_filter(uprobe->consumers))
> +			if (consumer_filter(uprobe->consumers,
> +					UPROBE_FILTER_REGISTER, mm))
>  				err = install_breakpoint(uprobe, mm, vma, info->vaddr);
>  		} else if (test_bit(MMF_HAS_UPROBES, &mm->flags)) {
> -			if (!filter_chain(uprobe))
> +			if (!filter_chain(uprobe,
> +					UPROBE_FILTER_UNREGISTER, mm))
>  				err |= remove_breakpoint(uprobe, mm, info->vaddr);
>  		}
> 
> @@ -968,7 +972,7 @@ int uprobe_mmap(struct vm_area_struct *vma)
>  	 */
>  	list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {
>  		if (!fatal_signal_pending(current) &&
> -		    filter_chain(uprobe)) {
> +		    filter_chain(uprobe, UPROBE_FILTER_MMAP, vma->vm_mm)) {
>  			unsigned long vaddr = offset_to_vaddr(vma, uprobe->offset);
>  			install_breakpoint(uprobe, vma->vm_mm, vma, vaddr);
>  		}
> -- 
> 1.5.5.1
>