From: Miroslav Benes <mbenes@suse.cz>
To: Song Liu <song@kernel.org>
Cc: live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
jpoimboe@kernel.org, jikos@kernel.org, pmladek@suse.com,
x86@kernel.org, joe.lawrence@redhat.com,
linuxppc-dev@lists.ozlabs.org,
Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH v6] livepatch: Clear relocation targets on a module removal
Date: Fri, 9 Dec 2022 13:55:29 +0100 (CET) [thread overview]
Message-ID: <alpine.LSU.2.21.2212091352370.18933@pobox.suse.cz> (raw)
In-Reply-To: <20220901171252.2148348-1-song@kernel.org>
Hi,
first thank you for taking over and I also appologize for not replying
much sooner.
On Thu, 1 Sep 2022, Song Liu wrote:
> From: Miroslav Benes <mbenes@suse.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'
>
> He also proposed three different solutions. We could remove the error
> check in apply_relocate_add() introduced by commit eda9cec4c9a1
> ("x86/module: Detect and skip invalid relocations"). However the check
> is useful for detecting corrupted modules.
>
> We could also deny the patched modules to be removed. If it proved to be
> a major drawback for users, we could still implement a different
> approach. The solution would also complicate the existing code a lot.
>
> We thus decided to reverse the relocation patching (clear all relocation
> targets on x86_64). The solution is not
> universal and is too much arch-specific, but it may prove to be simpler
> in the end.
>
> Reported-by: Josh Poimboeuf <jpoimboe@redhat.com>
> Signed-off-by: Miroslav Benes <mbenes@suse.cz>
> Signed-off-by: Song Liu <song@kernel.org>
Petr has commented on the code aspects. I will just add that s390x was not
dealt with at the time because there was no live patching support for
s390x back then if I remember correctly and my notes do not lie. The same
applies to powerpc32. I think that both should be fixed as well with this
patch. It might also help to clean up the ifdeffery in the patch a bit.
Miroslav
next prev parent reply other threads:[~2022-12-09 12:55 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-01 17:12 [PATCH v6] livepatch: Clear relocation targets on a module removal Song Liu
2022-11-17 22:06 ` Song Liu
2022-11-18 16:24 ` Petr Mladek
2022-11-18 17:14 ` Song Liu
2022-11-21 15:32 ` Joe Lawrence
2022-11-21 16:32 ` Song Liu
2022-11-29 1:57 ` Song Liu
2022-12-09 11:41 ` powerpc-part: was: " Petr Mladek
2022-12-09 19:59 ` Song Liu
2022-12-12 17:11 ` Petr Mladek
2022-12-12 22:22 ` Song Liu
2022-12-13 8:13 ` Song Liu
2022-12-13 13:29 ` Petr Mladek
2022-12-13 22:19 ` Joe Lawrence
2022-12-13 19:31 ` Song Liu
2022-12-09 12:36 ` x86 part: " Petr Mladek
2022-12-09 12:49 ` Miroslav Benes
2022-12-09 13:54 ` Petr Mladek
2022-12-09 14:20 ` Petr Mladek
2022-12-09 18:21 ` Song Liu
2022-12-09 12:55 ` Miroslav Benes [this message]
2022-12-09 18:30 ` Song Liu
2022-12-09 18:51 ` Christophe Leroy
2022-12-09 19:24 ` Song Liu
2022-12-12 8:16 ` Miroslav Benes
2022-12-13 8:28 ` Song Liu
2022-12-13 14:37 ` Petr Mladek
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