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 BC2DEC433FE for ; Thu, 25 Nov 2021 10:09:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354573AbhKYKNJ (ORCPT ); Thu, 25 Nov 2021 05:13:09 -0500 Received: from smtp-out1.suse.de ([195.135.220.28]:46158 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354382AbhKYKLJ (ORCPT ); Thu, 25 Nov 2021 05:11:09 -0500 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 4061C21954; Thu, 25 Nov 2021 10:07:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1637834877; 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; bh=egtWqavi5e/lfcU1EU6RtNwK3p+JN+8aD5azguEUeug=; b=REFfTzIV3E0wOzzjQtFOEGHXsaIphgNxvLU9bbyeVGnlbREatZU8UDHRxdp5IuQQxqP95N 5WRWrQcLVEW6NLPaw1hlSPyJCeLhI9fnoiFdYfGwj/uZ8i1KcZq/5qTt1q+qJPgQyzT5mj urpqX3tK/gT12mR81Q2/J3fu+vJqWKc= Received: from suse.cz (unknown [10.100.216.66]) (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 26641A3B81; Thu, 25 Nov 2021 10:07:57 +0000 (UTC) Date: Thu, 25 Nov 2021 11:07:56 +0100 From: Petr Mladek To: Joe Lawrence Cc: Miroslav Benes , Josh Poimboeuf , jikos@kernel.org, peterz@infradead.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, shuah@kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH 2/3] livepatch: Allow user to specify functions to search for on a stack Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <40edd48c-6f45-29e3-4749-be37fb61afba@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On Mon 2021-11-22 10:53:21, Joe Lawrence wrote: > On 11/22/21 2:57 AM, Miroslav Benes wrote: > > On Fri, 19 Nov 2021, Josh Poimboeuf wrote: > > > >> Thanks for doing this! And at peterz-esque speed no less :-) > >> > >> On Fri, Nov 19, 2021 at 10:03:26AM +0100, Miroslav Benes wrote: > >>> livepatch's consistency model requires that no live patched function > >>> must be found on any task's stack during a transition process after a > >>> live patch is applied. It is achieved by walking through stacks of all > >>> blocked tasks. > >>> > >>> The user might also want to define more functions to search for without > >>> them being patched at all. It may either help with preparing a live > >>> patch, which would otherwise require additional touches to achieve the > >>> consistency > >> > >> Do we have any examples of this situation we can add to the commit log? > > > > I do not have anything at hand. Joe, do you remember the case you > > mentioned previously about adding a nop to a function? > > Maybe adding a hypothetical scenario to the commit log would suffice? I wonder if we could describe a scenario based on the thread about .cold code variants, see https://lore.kernel.org/all/20211112015003.pefl656m3zmir6ov@treble/ This feature would allow to safely livepatch already released kernels where the unwinder is not able to reliably detect a newly discovered problems. > >>> or it can be used to overcome deficiencies the stack > >>> checking inherently has. For example, GCC may optimize a function so > >>> that a part of it is moved to a different section and the function would > >>> jump to it. This child function would not be found on a stack in this > >>> case, but it may be important to search for it so that, again, the > >>> consistency is achieved. > >>> > >>> Allow the user to specify such functions on klp_object level. > >>> > >>> Signed-off-by: Miroslav Benes > >>> --- > >>> include/linux/livepatch.h | 11 +++++++++++ > >>> kernel/livepatch/core.c | 16 ++++++++++++++++ > >>> kernel/livepatch/transition.c | 21 ++++++++++++++++----- > >>> 3 files changed, 43 insertions(+), 5 deletions(-) > >>> > >>> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h > >>> index 2614247a9781..89df578af8c3 100644 > >>> --- a/include/linux/livepatch.h > >>> +++ b/include/linux/livepatch.h > >>> @@ -106,9 +106,11 @@ struct klp_callbacks { > >>> * struct klp_object - kernel object structure for live patching > >>> * @name: module name (or NULL for vmlinux) > >>> * @funcs: function entries for functions to be patched in the object > >>> + * @funcs_stack: function entries for functions to be stack checked > >> > >> So there are two arrays/lists of 'klp_func', and two implied meanings of > >> what a 'klp_func' is and how it's initialized. > >> > >> Might it be simpler and more explicit to just add a new external field > >> to 'klp_func' and continue to have a single 'funcs' array? Similar to > >> what we already do with the special-casing of 'nop', except it would be > >> an external field, e.g. 'no_patch' or 'stack_only'. > > I'll add that the first thing that came to mind when you raised this > feature idea in the other thread was to support existing klp_funcs array > with NULL new_func's. Please, solve this with the extra flag, e.g. .stack_only, as already suggested. It will help to distinguish mistakes and intentions. Also it will allow to find these symbols by grep. > I didn't go look to see how invasive it would be, > but it will be interesting to see if a single list approach turns out > any simpler for v2. I am not sure either. But I expect that it will be easier than the extra array. Best Regards, Petr