linux-kernel - Re: [PATCH v2 2/2] uprobes, x86: Fix _TIF_UPROBE vs _TIF_NOTIFY

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Message-ID: <20141114060848.GB12682@linux.vnet.ibm.com>
Date:	Fri, 14 Nov 2014 11:38:48 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Borislav Petkov <bp@...en8.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Tony Luck <tony.luck@...el.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH v2 2/2] uprobes, x86: Fix _TIF_UPROBE vs
 _TIF_NOTIFY_RESUME

* Andy Lutomirski <luto@...capital.net> [2014-11-13 14:31:21]:

> x86 call do_notify_resume on paranoid returns if TIF_UPROBE is set
> but not on non-paranoid returns.  I suspect that this is a mistake
> and that the code only works because int3 is paranoid.
> 
> Setting _TIF_NOTIFY_RESUME in the uprobe code was probably a
> workaround for the x86 bug.  With that bug fixed, we can remove

> _TIF_NOTIFY_RESUME from the uprobes code.
> 
> Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> Reported-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Andy Lutomirski <luto@...capital.net>
> ---
>  arch/x86/include/asm/thread_info.h | 2 +-
>  kernel/events/uprobes.c            | 1 -
>  2 files changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
> index 854053889d4d..547e344a6dc6 100644
> --- a/arch/x86/include/asm/thread_info.h
> +++ b/arch/x86/include/asm/thread_info.h
> @@ -141,7 +141,7 @@ struct thread_info {
>  /* Only used for 64 bit */
>  #define _TIF_DO_NOTIFY_MASK						\
>  	(_TIF_SIGPENDING | _TIF_MCE_NOTIFY | _TIF_NOTIFY_RESUME |	\
> -	 _TIF_USER_RETURN_NOTIFY)
> +	 _TIF_USER_RETURN_NOTIFY | _TIF_UPROBE)


The comment above says only for 64 bit. So would this still work for
i386?

> 
>  /* flags to check in __switch_to() */
>  #define _TIF_WORK_CTXSW							\
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 1d0af8a2c646..ed8f2cde34c5 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1640,7 +1640,6 @@ bool uprobe_deny_signal(void)
>  		if (__fatal_signal_pending(t) || arch_uprobe_xol_was_trapped(t)) {
>  			utask->state = UTASK_SSTEP_TRAPPED;
>  			set_tsk_thread_flag(t, TIF_UPROBE);
> -			set_tsk_thread_flag(t, TIF_NOTIFY_RESUME);
>  		}
>  	}
> 
> -- 
> 1.9.3
> 

-- 
Thanks and Regards
Srikar Dronamraju

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