From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Miroslav Benes <mbenes@suse.cz>
Cc: jikos@kernel.org, pmladek@suse.com, joe.lawrence@redhat.com,
nstange@suse.de, live-patching@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v2 1/3] livepatch: Clear relocation targets on a module removal
Date: Wed, 2 Oct 2019 13:18:17 -0500 [thread overview]
Message-ID: <20191002181817.xpiqiisg5ybtwhru@treble> (raw)
In-Reply-To: <20190905124514.8944-2-mbenes@suse.cz>
On Thu, Sep 05, 2019 at 02:45:12PM +0200, Miroslav Benes 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.
>
> 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, or return back nops on powerpc). 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>
Since we decided to fix late module patching at LPC, the commit message
and clear_relocate_add() should both probably clarify that these
functions are hacks which are relatively temporary, until we fix the
root cause.
But this patch gives me a bad feeling :-/ Not that I have a better
idea.
Has anybody seen this problem in the real world? If not, maybe we'd be
better off just pretending the problem doesn't exist for now.
--
Josh
next prev parent reply other threads:[~2019-10-02 18:18 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-05 12:45 [RFC PATCH v2 0/3] livepatch: Clear relocation targets on a module removal Miroslav Benes
2019-09-05 12:45 ` [RFC PATCH v2 1/3] " Miroslav Benes
2019-10-02 13:22 ` Petr Mladek
2019-10-03 8:55 ` Miroslav Benes
2019-10-02 18:18 ` Josh Poimboeuf [this message]
2019-10-03 9:17 ` Miroslav Benes
2019-09-05 12:45 ` [RFC PATCH v2 2/3] livepatch: Unify functions for writing and clearing object relocations Miroslav Benes
2019-10-02 13:35 ` Petr Mladek
2019-09-05 12:45 ` [RFC PATCH v2 3/3] livepatch: Clean up klp_update_object_relocations() return paths Miroslav Benes
2019-10-02 13:46 ` Petr Mladek
2019-10-03 9:08 ` Miroslav Benes
2019-10-01 12:30 ` [RFC PATCH v2 0/3] livepatch: Clear relocation targets on a module removal Miroslav Benes
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