Re: [GIT PULL] x86/urgent for v5.11-rc7

[Miroslav Benes]

On Tue, 9 Feb 2021, Steven Rostedt wrote:

> On Tue, 9 Feb 2021 09:32:34 +0100 (CET)
> Miroslav Benes <mbenes@xxxxxxx> wrote:
> 
> > powerpc has this
> > 
> > static inline unsigned long klp_get_ftrace_location(unsigned long faddr)                                               
> > {                                                                                                                      
> >         /*                                                                                                             
> >          * Live patch works only with -mprofile-kernel on PPC. In this case,                                           
> >          * the ftrace location is always within the first 16 bytes.                                                    
> >          */                                                                                                            
> >         return ftrace_location_range(faddr, faddr + 16);                                                               
> > }                                                                                                                      
> > 
> > > > I suppose the trivial fix is to see if it points to endbr64 and if so,
> > > > increment the addr by the length of that.  
> > > 
> > > I thought of that too. But one thing that may be possible, is to use
> > > kallsym. I believe you can get the range of a function (start and end of
> > > the function) from kallsyms. Then ask ftrace for the addr in that range
> > > (there should only be one).  
> > 
> > And we can do this if a hard-coded value live above is not welcome. If I 
> > remember correctly, we used to have exactly this in the old versions of 
> > kGraft. We walked through all ftrace records, called 
> > kallsyms_lookup_size_offset() on every record's ip and if the offset+ip 
> > matched faddr (in this case), we returned the ip.
> 
> Either way is fine. Question is, should we just wait till CET is
> implemented for the kernel before making any of these changes? Just knowing
> that we have a solution to handle it may be good enough for now.

I'd prefer it to be a part of CET enablement patch set.

Miroslav