linux-kernel - Re: [PATCH] uprobe: Add uprobe_pre/post_sstep_notifier to NOKPROBE

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Message-Id: <20160803004524.760a8398c7525852bf26a29d@kernel.org>
Date:	Wed, 3 Aug 2016 00:45:24 +0900
From:	Masami Hiramatsu <mhiramat@...nel.org>
To:	Pratyush Anand <panand@...hat.com>
Cc:	linux-kernel@...r.kernel.org, oleg@...hat.com,
	srikar@...ux.vnet.ibm.com,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] uprobe: Add uprobe_pre/post_sstep_notifier to
 NOKPROBE_SYMBOL

On Tue,  2 Aug 2016 12:14:06 +0530
Pratyush Anand <panand@...hat.com> wrote:

> uprobe_pre_sstep_notifier and uprobe_post_sstep_notifier are called from
> debug exception handler, so blacklist them for kprobing.

Actually, these exception notifers are kicked only if the debug exception
is not related to kprobes (at least on x86). In that case, we don't have
to take care about that. Or, would you hit any problem on it?

IOW, where do we have to prohibit kprobes are, the code path from where 
right after the breakpoint (debug) exception is occurred, to where right
before the kprobe is handled. After that, it should be safe.

Thank you,


> 
> Signed-off-by: Pratyush Anand <panand@...hat.com>
> ---
>  kernel/events/uprobes.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index b7a525ab2083..206e594cb65e 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -37,6 +37,7 @@
>  #include <linux/percpu-rwsem.h>
>  #include <linux/task_work.h>
>  #include <linux/shmem_fs.h>
> +#include <linux/kprobes.h>
>  
>  #include <linux/uprobes.h>
>  
> @@ -1997,6 +1998,7 @@ int uprobe_pre_sstep_notifier(struct pt_regs *regs)
>  	set_thread_flag(TIF_UPROBE);
>  	return 1;
>  }
> +NOKPROBE_SYMBOL(uprobe_pre_sstep_notifier);
>  
>  /*
>   * uprobe_post_sstep_notifier gets called in interrupt context as part of notifier
> @@ -2014,6 +2016,7 @@ int uprobe_post_sstep_notifier(struct pt_regs *regs)
>  	set_thread_flag(TIF_UPROBE);
>  	return 1;
>  }
> +NOKPROBE_SYMBOL(uprobe_post_sstep_notifier);
>  
>  static struct notifier_block uprobe_exception_nb = {
>  	.notifier_call		= arch_uprobe_exception_notify,
> -- 
> 2.5.5
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>