linux-kernel - Re: [PATCH v2]: perf/x86: store user space frame-pointer value on a sample

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Message-ID: <6be7739b-8c6c-bbd8-6866-a26d8d25266d@linux.intel.com>
Date:   Thu, 10 May 2018 13:29:28 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org, Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v2]: perf/x86: store user space frame-pointer value on a
 sample

Hi,

On 10.05.2018 13:14, Peter Zijlstra wrote:
> On Thu, May 10, 2018 at 12:42:38PM +0300, Alexey Budankov wrote:
>>> The Changelog needs to state that user_regs->bp is in fact valid and
>>
>> That actually was tested on binaries compiled without and with BP exposed 
>> and in the latter case proved the value of that change.
> 
> Mostly works is not the same as 'always initialized', if there are entry
> paths that do not store that register, then using the value might leak
> values from the kernel stack, which would be bad.

Yep, absolutely agree. Extra care needs to be taken here.

> 
> But like said, I think much of the kernel entry code was sanitized with
> the PTI effort and I suspect things are in fact fine now, but lets wait
> for Andy to confirm.
> 

Thanks,
Alexey