linux-kernel - Re: [PATCH v9] livepatch: Clear relocation targets on a module removal

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Date:   Thu, 19 Jan 2023 11:06:35 -0800
From:   Song Liu <song@...nel.org>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org,
        live-patching@...r.kernel.org, x86@...nel.org, jikos@...nel.org,
        pmladek@...e.com, joe.lawrence@...hat.com,
        Miroslav Benes <mbenes@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v9] livepatch: Clear relocation targets on a module removal

On Wed, Jan 18, 2023 at 2:08 PM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
>
> On Wed, Jan 18, 2023 at 12:47:28PM -0800, Song Liu wrote:
> > From: Miroslav Benes <mbenes@...e.cz>
> >
> > Josh reported a bug:
> >
> >   When the object to be patched is a module, and that module is
> >   rmmod'ed and reloaded, it fails to load with:
> >
> >   module: x86/modules: Skipping invalid relocation target, existing value is nonzero for type 2, loc 00000000ba0302e9, val ffffffffa03e293c
> >   livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8)
> >   livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd'
> >
> >   The livepatch module has a relocation which references a symbol
> >   in the _previous_ loading of nfsd. When apply_relocate_add()
> >   tries to replace the old relocation with a new one, it sees that
> >   the previous one is nonzero and it errors out.
> >
> >   On ppc64le, we have a similar issue:
> >
> >   module_64: livepatch_nfsd: Expected nop after call, got e8410018 at e_show+0x60/0x548 [livepatch_nfsd]
> >   livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8)
> >   livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd'
>
> Shouldn't there also be a fix for this powerpc issue?

There was a working version, but it was not very clean. We couldn't agree
on the path forward for powerpc, so we are hoping to ship the fix to x86 (and
s390?) first [1].

Thanks,
Song

[1] https://lore.kernel.org/live-patching/Y7hLvpHqgY0oJ4GY@alley/#t