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 S1753427AbdK0Qqu (ORCPT <rfc822;w@1wt.eu>);
        Mon, 27 Nov 2017 11:46:50 -0500
Received: from bombadil.infradead.org ([65.50.211.133]:42341 "EHLO
        bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1753068AbdK0Qqt (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 27 Nov 2017 11:46:49 -0500
Date: Mon, 27 Nov 2017 17:46:39 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Jiri Olsa <jolsa@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Namhyung Kim <namhyung@kernel.org>, David Ahern <dsahern@gmail.com>,
        Andi Kleen <ak@linux.intel.com>,
        Milind Chabbi <chabbi.milind@gmail.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Hari Bathini <hbathini@linux.vnet.ibm.com>,
        Jin Yao <yao.jin@linux.intel.com>, Kan Liang <kan.liang@intel.com>,
        Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>,
        Oleg Nesterov <onestero@redhat.com>, Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH 4/6] hw_breakpoint: Factor out
 __modify_user_hw_breakpoint function
Message-ID: <20171127164639.3ymnc6io3eae7n4c@hirez.programming.kicks-ass.net>
References: <20171127162133.21163-1-jolsa@kernel.org>
 <20171127162133.21163-5-jolsa@kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20171127162133.21163-5-jolsa@kernel.org>
User-Agent: NeoMutt/20170609 (1.8.3)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, Nov 27, 2017 at 05:21:31PM +0100, Jiri Olsa wrote:
> +static int __modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
> +{
> +	u64 old_addr = bp->attr.bp_addr;
> +	u64 old_len  = bp->attr.bp_len;
> +	int old_type = bp->attr.bp_type;
> +	bool modify  = attr->bp_type != old_type;
> +	int err = 0;
> +
> +	bp->attr.bp_addr = attr->bp_addr;
> +	bp->attr.bp_type = attr->bp_type;
> +	bp->attr.bp_len  = attr->bp_len;
> +
> +	err = validate_hw_breakpoint(bp);
> +	if (!err && modify)
> +		err = modify_bp_slot(bp, old_type);
> +
> +	if (err) {
> +		bp->attr.bp_addr = old_addr;
> +		bp->attr.bp_type = old_type;
> +		bp->attr.bp_len  = old_len;
> +		return err;
> +	}
> +
> +	bp->attr.disabled = attr->disabled;
> +	return 0;
> +}

I think this function is failing to check if anything else in the attr
changes.

For example, someone could have added PERF_SAMPLE_BRANCH_STACK. That's
something you'll fail to create breakpoints with, but this modification
would 'accept'.