linux-kernel - Re: [PATCH v2 2/9] livepatch: Apply vmlinux-specific KLP relocations early

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Date:   Mon, 20 Apr 2020 15:49:00 -0400
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Jessica Yu <jeyu@...nel.org>
Subject: Re: [PATCH v2 2/9] livepatch: Apply vmlinux-specific KLP relocations
 early

On Mon, Apr 20, 2020 at 02:11:17PM -0500, Josh Poimboeuf wrote:
> On Mon, Apr 20, 2020 at 03:01:41PM -0400, Joe Lawrence wrote:
> > > > ... apply_relocations() is also iterating over the section headers (the
> > > > diff context doesn't show it here, but i is an incrementing index over
> > > > sechdrs[]).
> > > > 
> > > > So if there is more than one KLP relocation section, we'll process them
> > > > multiple times.  At least the x86 relocation code will detect this and
> > > > fail the module load with an invalid relocation (existing value not
> > > > zero).
> > > 
> > > Ah, yes, good catch!
> > > 
> > 
> > The same test case passed with a small modification to push the foreach
> > KLP section part to a kernel/livepatch/core.c local function and
> > exposing the klp_resolve_symbols() + apply_relocate_add() for a given
> > section to kernel/module.c.  Something like following...
> 
> I came up with something very similar, though I named them
> klp_apply_object_relocs() and klp_apply_section_relocs() and changed the
> argument order a bit (module first).  Since it sounds like you have a
> test, could you try this one?
> 

LGTM.  I have a few klp-convert selftests that I've been slowly
tinkering on and they all load/run successfully with this version. :)

-- Joe