From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1754512AbdC1HE1 (ORCPT <rfc822;w@1wt.eu>);
        Tue, 28 Mar 2017 03:04:27 -0400
Received: from mail-wr0-f194.google.com ([209.85.128.194]:32850 "EHLO
        mail-wr0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1754306AbdC1HEZ (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 28 Mar 2017 03:04:25 -0400
Date: Tue, 28 Mar 2017 09:04:19 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
        "David S . Miller" <davem@davemloft.net>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Ye Xiaolong <xiaolong.ye@intel.com>
Subject: Re: [RFC PATCH tip/master V2 4/8] kprobes/x86: Do not modify
 singlestep buffer while resuming
Message-ID: <20170328070419.GA27268@gmail.com>
References: <149060091581.12303.13449343279538504544.stgit@devbox>
 <149060119780.12303.15731372653870703672.stgit@devbox>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <149060119780.12303.15731372653870703672.stgit@devbox>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


* Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Do not modify singlestep execution buffer (kprobe.ainsn.insn)
> while resuming from single-stepping, instead, modifies
> the buffer to add a jump back instruction at preparing
> buffer.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  arch/x86/kernel/kprobes/core.c |   42 +++++++++++++++++++---------------------
>  1 file changed, 20 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 6327f95..ea3b8e5 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -399,23 +399,36 @@ int __copy_instruction(u8 *dest, u8 *src)
>  	return length;
>  }
>  
> +/* Prepare reljump right after instruction to boost */
> +static void prepare_boost(struct kprobe *p, int length)
> +{
> +	if (can_boost(p->ainsn.insn, p->addr) &&
> +	    MAX_INSN_SIZE - length >= RELATIVEJUMP_SIZE) {
> +		/*
> +		 * These instructions can be executed directly if it
> +		 * jumps back to correct address.
> +		 */
> +		synthesize_reljump((void *)p->ainsn.insn + length,
> +				   (void *)p->addr + length);
> +		p->ainsn.boostable = 1;
> +	} else
> +		p->ainsn.boostable = -1;

Those imbalanced curly braces are not proper kernel style.

Also, is the (void *) cast required? arch.insns ought to be void * already, right? 
(I haven't checking whether that's true for all architectures.)

Btw., the original code had the curly braces right:

> -	if (p->ainsn.boostable == 0) {
> -		if ((regs->ip > copy_ip) &&
> -		    (regs->ip - copy_ip) + 5 < MAX_INSN_SIZE) {
> -			/*
> -			 * These instructions can be executed directly if it
> -			 * jumps back to correct address.
> -			 */
> -			synthesize_reljump((void *)regs->ip,
> -				(void *)orig_ip + (regs->ip - copy_ip));
> -			p->ainsn.boostable = 1;
> -		} else {
> -			p->ainsn.boostable = -1;
> -		}
> -	}

Thanks,

	Ingo