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

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Message-ID: <20230118220812.dvztwhlmliypefha@treble>
Date:   Wed, 18 Jan 2023 14:08:12 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Song Liu <song@...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 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?

-- 
Josh