linux-kernel - Re: [PATCH 4/6] hw_breakpoint: Factor out __modify_user_hw

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Message-ID: <20171127173417.eokpkznt65yreoav@hirez.programming.kicks-ass.net>
Date:   Mon, 27 Nov 2017 18:34:17 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Milind Chabbi <chabbi.milind@...il.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>,
        Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
        Oleg Nesterov <onestero@...hat.com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH 4/6] hw_breakpoint: Factor out
 __modify_user_hw_breakpoint function

On Mon, Nov 27, 2017 at 06:25:32PM +0100, Jiri Olsa wrote:
> On Mon, Nov 27, 2017 at 06:12:03PM +0100, Peter Zijlstra wrote:
> > But what validates the input attr is the same as the event attr, aside
> > from those fields?
> 
> we don't.. the attr serves as a holder to carry those fields
> into the function

Then that's a straight up bug.

> the current kernel interface does not check anything else

Not enough, if the new attr would fail perf_event_open() it should also
fail this modify thing.

> there's one more check in the ioctl path, we check the
> type in perf_event_modify_attr:
> 
>         if (event->attr.type != attr->type)
>                 return -EINVAL;

Note how hw_breakpoint_event_init() tests has_branch_stack() and fails
on it.

Ideally we should check a whole lot more and fail, but alas..