Messages in this thread | | | Date | Thu, 24 Oct 2019 15:16:34 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4 15/16] module: Move where we mark modules RO,X |
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On Wed, Oct 23, 2019 at 12:00:25PM -0500, Josh Poimboeuf wrote:
> > This then raises a number of questions: > > > > 1) why is that RELA (that obviously does not depend on any module) > > applied so late? > > Good question. The 'pv_ops' symbol is exported by the core kernel, so I > can't see any reason why we'd need to apply that rela late. In theory, > kpatch-build isn't supposed to convert that to a klp rela. Maybe > something went wrong in the patch creation code. > > I'm also questioning why we even need to apply the parainstructions > section late. Maybe we can remove that apply_paravirt() call > altogether, along with .klp.arch.parainstruction sections. > > I'll need to look into it...
Right, that really should be able to run early. Esp. after commit
11e86dc7f274 ("x86/paravirt: Detect over-sized patching bugs in paravirt_patch_call()")
paravirt patching is unconditional. We _never_ run with the indirect call except very early boot, but modules should have them patched way before their init section runs.
We rely on this for spectre-v2 and friends.
> > 3) Is there ever a possible module-dependent RELA to a paravirt / > > alternative site? > > Good question...
> > Then for 3) we only have alternatives left, and I _think_ it unlikely to > > be the case, but I'll have to have a hard look at that. > > I'm not sure about alternatives, but maybe we can enforce such > limitations with tooling and/or kernel checks.
Right, so on IRC you implied you might have some additional details on how alternatives were affected; did you manage to dig that up?
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