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Subject: Re: [PATCH v2]: perf/x86: store user space frame-pointer value on a
 sample
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Ingo Molnar <mingo@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-perf-users@vger.kernel.org, Andy Lutomirski <luto@kernel.org>
References: <31205dc8-b756-e12b-0249-2ed06c2db9c9@linux.intel.com>
 <20180509145436.GV12217@hirez.programming.kicks-ass.net>
 <3ecedd91-1c01-6fc5-4648-89eaf5ff0930@linux.intel.com>
 <20180510101406.GA12217@hirez.programming.kicks-ass.net>
From:   Alexey Budankov <alexey.budankov@linux.intel.com>
Message-ID: <6be7739b-8c6c-bbd8-6866-a26d8d25266d@linux.intel.com>
Date:   Thu, 10 May 2018 13:29:28 +0300
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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