[lkml]   [2018]   [May]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v2]: perf/x86: store user space frame-pointer value on a sample

> On May 21, 2018, at 9:51 AM, Alexey Budankov <> wrote:
> Hi Andy,
>> On 21.05.2018 17:14, Andy Lutomirski wrote:
>>> On May 21, 2018, at 5:44 AM, Alexey Budankov <> wrote:
>>> Hi Peter,
>>>> 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.
>>>> 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.
>>> It looks like, these days, all registers are saved on system calls, just
>>> like you anticipated.
>>> So BP register value might be stored into the Perf trace on a sample.
>>> Andy?
>> Hmm, I thought I replied. Yes, they are indeed all saved, but I’m not very excited about committing to doing so forever. But storing BP should be fine.
> Thanks for explicit confirmation regarding BP register.
> BTW, do you see any mean to prevent possible unattended regression?
> I guess it could be some compile time assertion or regression testing.

Write a selftest?

The whole perf user regs mechanism is buggy and fragile. I need to massively clean it up at some point.

> Thanks,
> Alexey

 \ /
  Last update: 2018-05-21 19:24    [W:0.081 / U:3.444 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site