From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 44D87C32793 for ; Wed, 18 Jan 2023 14:01:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230017AbjAROB0 (ORCPT ); Wed, 18 Jan 2023 09:01:26 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56096 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230038AbjAROBG (ORCPT ); Wed, 18 Jan 2023 09:01:06 -0500 Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2001:67c:2178:6::1c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B33B78728C for ; Wed, 18 Jan 2023 05:35:01 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id C840C3E8A6; Wed, 18 Jan 2023 13:34:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1674048899; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=QCnYNYnWqyOf6SsgnfN+3NvmiwWWWcMIPO/+zLa7vz8=; b=CFL1Tbn+9B1XUEITTT5oqyp+CmA2J5JqKBwCRS9pg4ZArLGefr+ZV6I+rjFcFboUy0gxsO WClhJ7GqlVADAX8akYZF1k5c5QDutQc3M/58VLg39UcK0VUCxmMv9ooD7cseFhMopA2sF0 G67mb6lPV0xBA5s5ZiEnqq+5FRhaj+o= Received: from suse.cz (unknown [10.100.201.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id A39D42C141; Wed, 18 Jan 2023 13:34:59 +0000 (UTC) Date: Wed, 18 Jan 2023 14:34:59 +0100 From: Petr Mladek To: Song Liu Cc: Miroslav Benes , X86 ML , live-patching@vger.kernel.org, jpoimboe@kernel.org, jikos@kernel.org, joe.lawrence@redhat.com, Josh Poimboeuf Subject: Re: [PATCH v8] livepatch: Clear relocation targets on a module removal Message-ID: References: <20230106200109.2546997-1-song@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Fri 2023-01-13 11:55:25, Song Liu wrote: > On Fri, Jan 13, 2023 at 1:18 AM Miroslav Benes wrote: > > > > Hi, > > > > On Fri, 6 Jan 2023, Song Liu wrote: > > > > > From: Miroslav Benes > > > > > > 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. > > > > > > Signed-off-by: Miroslav Benes > > > Signed-off-by: Song Liu > > > Reported-by: Josh Poimboeuf > > > > I would be fine if you just claimed the authorship (and include my > > Originally-by: tag for example), because you have reworked it quite a lot > > since my first attempts. > > I am ok with either way. Or maybe with > > Co-developed-by: Song Liu > > > > > > +int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs, > > > + const char *shstrtab, const char *strtab, > > > + unsigned int symndx, unsigned int secndx, > > > + const char *objname) > > > +{ > > > + return klp_write_section_relocs(pmod, sechdrs, shstrtab, strtab, symndx, > > > + secndx, objname, true); > > > } I think that I proposed this wrapper :-) > > Is this redirection needed somewhere? You could just replace > > klp_apply_section_relocs() with klp_write_section_relocs() in > > include/linux/livepatch.h and kernel/module/main.c. > > > > It may be cleaned up later. > > It might be a good practice to keep _write_ static in this file, and > only expose _apply_ (maybe also _clear_ in the future)? And I think that this was the reason. Also it looks better in kernel/module/main.c in apply_relocations() that calls few more *_apply_*reloc*() functions. The idea is that functions with the same naming pattern do the same operation. Also it is supposed to hide the true/false parameter and self-explain the meaning by the function name. > I don't have a strong preference either way. I would prefer to keep the wrapper. But I do not resist on it :-) Best Regards, Petr