> On May 21, 2018, at 5:44 AM, Alexey Budankov > <alexey.budan...@linux.intel.com> 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.
