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 X-Spam-Level: X-Spam-Status: No, score=-0.3 required=3.0 tests=DKIM_ADSP_CUSTOM_MED, DKIM_INVALID,DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B78B8C2D0B1 for ; Thu, 6 Feb 2020 13:10:06 +0000 (UTC) Received: from fraxinus.osuosl.org (smtp4.osuosl.org [140.211.166.137]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 7D88F214AF for ; Thu, 6 Feb 2020 13:10:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="vMNJk8Mf" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7D88F214AF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linux-kernel-mentees-bounces@lists.linuxfoundation.org Received: from localhost (localhost [127.0.0.1]) by fraxinus.osuosl.org (Postfix) with ESMTP id 1569785F80; Thu, 6 Feb 2020 13:10:06 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from fraxinus.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Q6j27eo-YHgu; Thu, 6 Feb 2020 13:10:05 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by fraxinus.osuosl.org (Postfix) with ESMTP id 8097785F51; Thu, 6 Feb 2020 13:10:05 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 6A89CC0881; Thu, 6 Feb 2020 13:10:05 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) by lists.linuxfoundation.org (Postfix) with ESMTP id C0421C013E for ; Thu, 6 Feb 2020 13:10:04 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id BA3A6879A3 for ; Thu, 6 Feb 2020 13:10:04 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id jlpz3xRvm3Mf for ; Thu, 6 Feb 2020 13:10:04 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-pj1-f66.google.com (mail-pj1-f66.google.com [209.85.216.66]) by hemlock.osuosl.org (Postfix) with ESMTPS id EE79687860 for ; Thu, 6 Feb 2020 13:10:03 +0000 (UTC) Received: by mail-pj1-f66.google.com with SMTP id q39so2541910pjc.0 for ; Thu, 06 Feb 2020 05:10:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=y4Pa1L5RARQgqvzqz59p+CvaGETvYZ1UCLM+Mc5CN84=; b=vMNJk8MfX7MLWGNRzhL/SmImsM+kmBcpOPmAlsdIRKsmSKG9yfmkajIS9O6Xs7iTOD RO807KsIZSZff/TYq/lxeYvIlIpfghegRdOIXk/DMH0+m6y2h/fWmV//y6lYeqJt2KYG NGYhXSrpFHYZSQHsLhr3mGaY8V6OpaloCpHlnVWoXcEnENl+7tSyuG8Za5tuXyu8btMZ JWhcJGT/zZNQq62O/S/Ih3VI/eB7g+z7yEhuddQ9JwTP3f3xVx7nIK1JSMD3lQicJ/Oc /ATPSFnPEhtn6Rk8+slgmgP2zgBQKiZVe6Xv2E8m/6loSQDTtQj/PRpibC8VCpff2+Bs DoHw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=y4Pa1L5RARQgqvzqz59p+CvaGETvYZ1UCLM+Mc5CN84=; b=a3EKtGo0XudUy0LkaBo3gZv15xQrex/jQC2dxF/hy1yfWEuYRWlHxGQBeCEGxdcqPM 1duL2dGFTxCEtAMfZ5/FXFk75lt5nUPBMv3rVRlwgEDa0yh4UkFpjKqsakRdBgAYiaJc LC2vQFS99aFLDl6jGVSh0ueV8GIPf4v1QMHL3hr8AknjuSJObHdHaCQpo3tMAlO7C9Pa u3ToVrKZ0vDsgl0PJbkuAyvSrrecsAWiY/0G1j0Q8fg49sdIza8tLvwe3iboE7N4Y/EH mO7eUJtnsHF6kZdxD0C75J/7vL9q8tQtLvp3/tPJCsjtKZFVW7iQMFHAwJVRC3wlHEPX HROQ== X-Gm-Message-State: APjAAAUQZQgNqFNMtAPZ6DseXTuCGblPMwazDojyE0V9lLpqWr8Q4O+m uDDwpEx+V6S7nmSwrCSbErk= X-Google-Smtp-Source: APXvYqwxOLxWA1l6OErju8aIUZL86BPGQWlMbFRKo5hSrHBWS6v4iWDEq2Kdys62jBSDVrAnzH+DbQ== X-Received: by 2002:a17:902:9f88:: with SMTP id g8mr3709690plq.100.1580994603439; Thu, 06 Feb 2020 05:10:03 -0800 (PST) Received: from workstation-portable ([103.211.17.39]) by smtp.gmail.com with ESMTPSA id t15sm2370459pgr.60.2020.02.06.05.09.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Feb 2020 05:10:02 -0800 (PST) Date: Thu, 6 Feb 2020 18:39:55 +0530 From: Amol Grover To: Joel Fernandes Message-ID: <20200206130955.GA3917@workstation-portable> References: <20200128072740.21272-1-frextrite@gmail.com> <20200128170426.GA10277@workstation-portable> <20200129065738.GA17486@workstation-portable> <20200206013251.GC55522@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200206013251.GC55522@google.com> Cc: Kees Cook , "Paul E . McKenney" , Jann Horn , Oleg Nesterov , James Morris , kernel list , David Howells , Shakeel Butt , Thomas Gleixner , linux-kernel-mentees@lists.linuxfoundation.org Subject: Re: [Linux-kernel-mentees] [PATCH] cred: Use RCU primitives to access RCU pointers X-BeenThere: linux-kernel-mentees@lists.linuxfoundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-kernel-mentees-bounces@lists.linuxfoundation.org Sender: "Linux-kernel-mentees" On Wed, Feb 05, 2020 at 08:32:51PM -0500, Joel Fernandes wrote: > On Wed, Jan 29, 2020 at 03:14:56PM +0100, Jann Horn wrote: > > On Wed, Jan 29, 2020 at 7:57 AM Amol Grover wrote: > > > On Tue, Jan 28, 2020 at 08:09:17PM +0100, Jann Horn wrote: > > > > On Tue, Jan 28, 2020 at 6:04 PM Amol Grover wrote: > > > > > On Tue, Jan 28, 2020 at 10:30:19AM +0100, Jann Horn wrote: > > > > > > On Tue, Jan 28, 2020 at 8:28 AM Amol Grover wrote: > > > > > > > task_struct.cred and task_struct.real_cred are annotated by __rcu, > > > > > > > > > > > > task_struct.cred doesn't actually have RCU semantics though, see > > > > > > commit d7852fbd0f0423937fa287a598bfde188bb68c22. For task_struct.cred, > > > > > > it would probably be more correct to remove the __rcu annotation? > > > > > > > > > > Hi Jann, > > > > > > > > > > I went through the commit you mentioned. If I understand it correctly, > > > > > ->cred was not being accessed concurrently (via RCU), hence, a non_rcu > > > > > flag was introduced, which determined if the clean-up should wait for > > > > > RCU grace-periods or not. And since, the changes were 'thread local' > > > > > there was no need to wait for an entire RCU GP to elapse. > > > > > > > > Yeah. > > > > > > > > > The commit too, as you said, mentions the removal of __rcu annotation. > > > > > However, simply removing the annotation won't work, as there are quite a > > > > > few instances where RCU primitives are used. Even get_current_cred() > > > > > uses RCU APIs to get a reference to ->cred. > > > > > > > > Luckily, there aren't too many places that directly access ->cred, > > > > since luckily there are helper functions like get_current_cred() that > > > > will do it for you. Grepping through the kernel, I see: > > [...] > > > > So actually, the number of places that already don't use RCU accessors > > > > is much higher than the number of places that use them. > > > > > > > > > So, currently, maybe we > > > > > should continue to use RCU APIs and leave the __rcu annotation in? > > > > > (Until someone who takes it on himself to remove __rcu annotation and > > > > > fix all the instances). Does that sound good? Or do you want me to > > > > > remove __rcu annotation and get the process started? > > > > > > > > I don't think it's a good idea to add more uses of RCU APIs for > > > > ->cred; you shouldn't "fix" warnings by making the code more wrong. > > > > > > > > If you want to fix this, I think it would be relatively easy to fix > > > > this properly - as far as I can tell, there are only seven places that > > > > you'll have to change, although you may have to split it up into three > > > > patches. > > > > > > Thank you for the detailed analysis. I'll try my best and send you a > > > patch. > > Amol, Jann, if I understand the discussion correctly, objects ->cred > point (the subjective creds) are never (or never need to be) RCU-managed. > This makes sense in light of the commit Jann pointed out > (d7852fbd0f0423937fa287a598bfde188bb68c22). > > How about the following diff as a starting point? > > 1. Remove all ->cred accessing happening through RCU primitive. > 2. Remove __rcu from task_struct ->cred > 3. Also I removed the whole non_rcu flag, and introduced a new put_cred_non_rcu() API > which places that task-synchronously use ->cred can overwrite. Callers > doing such accesses like access() can use this API instead. > > I have only build tested the below diff and it is likely buggy but Amol you > can use it as a starting point, or we can discuss more on this thread. > Thank you for starting this Joel! This will make our lives easier! I'll go through it once and get back to Jann's latest reply. Thanks Amol _______________________________________________ Linux-kernel-mentees mailing list Linux-kernel-mentees@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees