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

[Alexey Budankov]

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