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

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Message-ID: <CAMmz+Y=r3P9Lnk7-hPBkeGZ7E=dho0osB-jnhjAH6sqwSDXdwA@mail.gmail.com>
Date:   Mon, 27 Nov 2017 15:31:19 -0800
From:   Milind Chabbi <chabbi.milind@...il.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Milind Chabbi <chabbi.milind@...il.com>,
        Jiri Olsa <jolsa@...hat.com>, 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>,
        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 3:07 PM, Andi Kleen <ak@...ux.intel.com> wrote:
> On Mon, Nov 27, 2017 at 11:01:28PM +0100, Peter Zijlstra wrote:
>> On Mon, Nov 27, 2017 at 01:50:30PM -0800, Milind Chabbi wrote:
>> > The possible checks is infinite
>>
>> struct perf_event_attr is very much a finite data type.
>>
>> Something as simple as:
>>
>>       struct perf_event_attr tmp1 = new_attr, tmp2 = event->attr;
>>
>>       tmp1.bp_type = tmp2.bp_type;
>>       tmp1.bp_addr = tmp2.bp_addr;
>>       tmp1.bp_len  = tmp2.bp_len;
>>
>>       if (memcmp(&tmp1, &tmp2, sizeof(tmp1)))
>>               return -EINVAL;
>>
>> would actually do the checks __modify_user_hw_breakpoint() needs to do.
>
> It could fail with uninitialized padding.
>
>
> -Andi
>

Hm...
How about we zero out __reserved_1 and __reserved_2 before memcmp()?