From: Josh Poimboeuf <jpoimboe@kernel.org>
To: Song Liu <song@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-modules@vger.kernel.org,
live-patching@vger.kernel.org, x86@kernel.org,
Josh Poimboeuf <jpoimboe@redhat.com>,
Miroslav Benes <mbenes@suse.cz>, Petr Mladek <pmladek@suse.com>
Subject: Re: [PATCH v11 2/2] livepatch,x86: Clear relocation targets on a module removal
Date: Wed, 25 Jan 2023 11:03:36 -0800 [thread overview]
Message-ID: <20230125190336.utdb3tvyuy74vnap@treble> (raw)
In-Reply-To: <20230125185401.279042-2-song@kernel.org>
On Wed, Jan 25, 2023 at 10:54:01AM -0800, Song Liu wrote:
> 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.
>
> 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>
> Originally-by: Miroslav Benes <mbenes@suse.cz>
> Signed-off-by: Song Liu <song@kernel.org>
> Acked-by: Miroslav Benes <mbenes@suse.cz>
> Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
--
Josh
next prev parent reply other threads:[~2023-01-25 19:03 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-25 18:54 [PATCH v11 1/2] x86/module: remove unused code in __apply_relocate_add Song Liu
2023-01-25 18:54 ` [PATCH v11 2/2] livepatch,x86: Clear relocation targets on a module removal Song Liu
2023-01-25 19:03 ` Josh Poimboeuf [this message]
2023-01-27 13:46 ` Joe Lawrence
2023-01-25 19:03 ` [PATCH v11 1/2] x86/module: remove unused code in __apply_relocate_add Josh Poimboeuf
2023-01-27 13:45 ` Joe Lawrence
2023-02-03 13:33 ` Petr Mladek
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