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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id A164EC0015E for ; Tue, 1 Aug 2023 17:04:23 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2982894002D; Tue, 1 Aug 2023 13:04:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 221B2940010; Tue, 1 Aug 2023 13:04:23 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 09AAA94002D; Tue, 1 Aug 2023 13:04:23 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id E9104940010 for ; Tue, 1 Aug 2023 13:04:22 -0400 (EDT) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 7E6A1A060B for ; Tue, 1 Aug 2023 17:04:22 +0000 (UTC) X-FDA: 81076159164.11.796185B Received: from mail-wm1-f43.google.com (mail-wm1-f43.google.com [209.85.128.43]) by imf24.hostedemail.com (Postfix) with ESMTP id A47661823B3 for ; Tue, 1 Aug 2023 16:39:06 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=gmail.com header.s=20221208 header.b="PQ/9Wtxc"; spf=pass (imf24.hostedemail.com: domain of lstoakes@gmail.com designates 209.85.128.43 as permitted sender) smtp.mailfrom=lstoakes@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1690907946; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=9Q+FYlsdVjplvOSfu1dq3E3GzIaJTb8Vu7slqEF1uNU=; b=pzOFL3a09GjmvVvMRBBMelvKS7fL9t8TdDxGWtsqkTUVUBFINgSsej5OC7l48FcgYENMj+ P5DljDdpxe5kIgaFB4ikwau41lUNluIrffoFOe5W6k73YaGJEM1+cR4OOtgVBmMr/xWYET oUEtgNzqBH4Mec0XFLykLep5+Txl+xg= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1690907946; a=rsa-sha256; cv=none; b=aFH5RWUN0F+Iw0mjutaZuPyWmKS77YOY5eTyhQeL6VvbeIg6VbCMq5b8QDI1Y68ch/zQF5 Kwws3dRrc2rBYAPDddH9IXCSGA9RtoDjh4hOPwqOkHzgBOwigDeB9M6FILzck3wt15Kt6O LBMly7Ujn7rtekr68ZglFdZCqaNiTH8= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=gmail.com header.s=20221208 header.b="PQ/9Wtxc"; spf=pass (imf24.hostedemail.com: domain of lstoakes@gmail.com designates 209.85.128.43 as permitted sender) smtp.mailfrom=lstoakes@gmail.com; dmarc=pass (policy=none) header.from=gmail.com Received: by mail-wm1-f43.google.com with SMTP id 5b1f17b1804b1-3fe1a17f983so26186475e9.3 for ; Tue, 01 Aug 2023 09:39:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1690907945; x=1691512745; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=9Q+FYlsdVjplvOSfu1dq3E3GzIaJTb8Vu7slqEF1uNU=; b=PQ/9WtxcgKsHz11TgwxBlZXFedw159G32eIiWIQUC2W8imCUzwa0z69gSm99Nn8XzO 8YhcJPiguUh5h5KTdY13J4bo7WuUVmvPk+iyTEYw3u0VRUfA+Vcd/SojuIqlXz5cU8pX DLLqv6Fq8tz1EnzRZXDwtsGqUSHjUC4jrEquPNX4xqOCU2/lZQRB/f78AgHkBT1ieGLG dycGgWYrCxN8LcBYbsC6WdsNktq1jvO9sOmF5N0OUaNXxmE+vhwDytLDIN5pnRBnEP2c j+rzbXwOPee0gG28vv+TvUQ44D5nUsFi1a166Lo8XZzVGzIsX86phd4nr6Dv8oH0jgcd nbsw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1690907945; x=1691512745; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=9Q+FYlsdVjplvOSfu1dq3E3GzIaJTb8Vu7slqEF1uNU=; b=mIRYGEQLq01AKgEbt/vkgDVVDsqZlgVBYyZ3BjdzTNDZ0/zFwrk55SgDUxnbKpaWni Ewyl2BIlDUho1ECT3J36q0vWGNjgsOvyAD2DXq3xkUVD0m3kgYTBpo2VVyjo/VFLdWk4 KdeCO2AeXxBkgHCeTiCWwFgXSYz2jueCRZdTRgLn5INCEzImoVlYmCKun2Fbb+taD1p3 XQP/ONZ3Bhi14etb1hJPyy3qqfVS54dgjx18oFj/r3hNog/nfeozqRHkE6CscOYz8XQJ NESerCPgmsm+vOOq590ooRLahUR4ifKz8llW+ETfG/8mhzuCDFYid3Zn7J9pO89R90ZF 7+XQ== X-Gm-Message-State: ABy/qLZMR9EEZ6d0pWU75RszL0fZkTwKMeOb3ip4iQtYU52mZT+7yEdG aTG+o1f/S3OdT1XZXW6nSRM= X-Google-Smtp-Source: APBJJlFc5Vg3IQU7O9rEPNVuYWEM2agkv7AwA1Cbrec45/A1tySgo6OaaaphAZnmaJaupcAfxKHaww== X-Received: by 2002:a7b:ce90:0:b0:3fe:1aef:b9d8 with SMTP id q16-20020a7bce90000000b003fe1aefb9d8mr2764758wmj.14.1690907944448; Tue, 01 Aug 2023 09:39:04 -0700 (PDT) Received: from localhost ([2a00:23c5:dc8c:8701:1663:9a35:5a7b:1d76]) by smtp.gmail.com with ESMTPSA id m7-20020a05600c280700b003fe1afb99a9sm8453826wmb.11.2023.08.01.09.39.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Aug 2023 09:39:03 -0700 (PDT) Date: Tue, 1 Aug 2023 17:39:02 +0100 From: Lorenzo Stoakes To: David Hildenbrand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Baoquan He , Uladzislau Rezki , linux-fsdevel@vger.kernel.org, Jiri Olsa , Will Deacon , Mike Galbraith , Mark Rutland , wangkefeng.wang@huawei.com, catalin.marinas@arm.com, ardb@kernel.org, Linux regression tracking , regressions@lists.linux.dev, Matthew Wilcox , Liu Shixin , Jens Axboe , Alexander Viro , stable@vger.kernel.org Subject: Re: [PATCH] fs/proc/kcore: reinstate bounce buffer for KCORE_TEXT regions Message-ID: <525a3f14-74fa-4c22-9fca-9dab4de8a0c3@lucifer.local> References: <20230731215021.70911-1-lstoakes@gmail.com> <0af1bc20-8ba2-c6b6-64e6-c1f58d521504@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: A47661823B3 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: c5yq9oc69a7rehobuh76hf9juxkayebf X-HE-Tag: 1690907946-316985 X-HE-Meta: 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 PsJT7ff9 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Aug 01, 2023 at 06:34:26PM +0200, David Hildenbrand wrote: > On 01.08.23 18:33, Lorenzo Stoakes wrote: > > On Tue, Aug 01, 2023 at 11:05:40AM +0200, David Hildenbrand wrote: > > > On 31.07.23 23:50, Lorenzo Stoakes wrote: > > > > Some architectures do not populate the entire range categorised by > > > > KCORE_TEXT, so we must ensure that the kernel address we read from is > > > > valid. > > > > > > > > Unfortunately there is no solution currently available to do so with a > > > > purely iterator solution so reinstate the bounce buffer in this instance so > > > > we can use copy_from_kernel_nofault() in order to avoid page faults when > > > > regions are unmapped. > > > > > > > > This change partly reverts commit 2e1c0170771e ("fs/proc/kcore: avoid > > > > bounce buffer for ktext data"), reinstating the bounce buffer, but adapts > > > > the code to continue to use an iterator. > > > > > > > > Fixes: 2e1c0170771e ("fs/proc/kcore: avoid bounce buffer for ktext data") > > > > Reported-by: Jiri Olsa > > > > Closes: https://lore.kernel.org/all/ZHc2fm+9daF6cgCE@krava > > > > Cc: stable@vger.kernel.org > > > > Signed-off-by: Lorenzo Stoakes > > > > --- > > > > fs/proc/kcore.c | 26 +++++++++++++++++++++++++- > > > > 1 file changed, 25 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c > > > > index 9cb32e1a78a0..3bc689038232 100644 > > > > --- a/fs/proc/kcore.c > > > > +++ b/fs/proc/kcore.c > > > > @@ -309,6 +309,8 @@ static void append_kcore_note(char *notes, size_t *i, const char *name, > > > > static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter) > > > > { > > > > + struct file *file = iocb->ki_filp; > > > > + char *buf = file->private_data; > > > > loff_t *fpos = &iocb->ki_pos; > > > > size_t phdrs_offset, notes_offset, data_offset; > > > > size_t page_offline_frozen = 1; > > > > @@ -554,11 +556,22 @@ static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter) > > > > fallthrough; > > > > case KCORE_VMEMMAP: > > > > case KCORE_TEXT: > > > > + /* > > > > + * Sadly we must use a bounce buffer here to be able to > > > > + * make use of copy_from_kernel_nofault(), as these > > > > + * memory regions might not always be mapped on all > > > > + * architectures. > > > > + */ > > > > + if (copy_from_kernel_nofault(buf, (void *)start, tsz)) { > > > > + if (iov_iter_zero(tsz, iter) != tsz) { > > > > + ret = -EFAULT; > > > > + goto out; > > > > + } > > > > /* > > > > * We use _copy_to_iter() to bypass usermode hardening > > > > * which would otherwise prevent this operation. > > > > */ > > > > > > Having a comment at this indentation level looks for the else case looks > > > kind of weird. > > > > Yeah, but having it indented again would be weird and seem like it doesn't > > apply to the block below, there's really no good spot for it and > > checkpatch.pl doesn't mind so I think this is ok :) > > > > > > > > (does that comment still apply?) > > > > Hm good point, actually, now we're using the bounce buffer we don't need to > > avoid usermode hardening any more. > > > > However since we've established a bounce buffer ourselves its still > > appropriate to use _copy_to_iter() as we know the source region is good to > > copy from. > > > > To make life easy I'll just respin with an updated comment :) > > I'm not too picky this time, no need to resend if everybody else is fine :P > Haha you know the classic Lorenzo respin spiral and want to avoid it I see ;) The comment is actually inaccurate now, so to avoid noise + make life easy (maybe) for Andrew here's a fix patch that just corrects the comment:- ----8<---- >From d2b8fb271f21b79048e5630699133f77a93d0481 Mon Sep 17 00:00:00 2001 From: Lorenzo Stoakes Date: Tue, 1 Aug 2023 17:36:08 +0100 Subject: [PATCH] fs/proc/kcore: correct comment Correct comment to be strictly correct about reasoning. Signed-off-by: Lorenzo Stoakes --- fs/proc/kcore.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c index 3bc689038232..23fc24d16b31 100644 --- a/fs/proc/kcore.c +++ b/fs/proc/kcore.c @@ -568,8 +568,8 @@ static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter) goto out; } /* - * We use _copy_to_iter() to bypass usermode hardening - * which would otherwise prevent this operation. + * We know the bounce buffer is safe to copy from, so + * use _copy_to_iter() directly. */ } else if (_copy_to_iter(buf, tsz, iter) != tsz) { ret = -EFAULT; -- 2.41.0