From patchwork Fri Nov 12 09:27:50 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 12616411 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A2809C433F5 for ; Fri, 12 Nov 2021 09:28:31 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5A02A61029 for ; Fri, 12 Nov 2021 09:28:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 5A02A61029 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id EEB3F6B0078; Fri, 12 Nov 2021 04:28:30 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id E9BB86B007B; Fri, 12 Nov 2021 04:28:30 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D8A7C6B007D; Fri, 12 Nov 2021 04:28:30 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0155.hostedemail.com [216.40.44.155]) by kanga.kvack.org (Postfix) with ESMTP id CBDD26B0078 for ; Fri, 12 Nov 2021 04:28:30 -0500 (EST) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 7D74D18033E64 for ; Fri, 12 Nov 2021 09:28:30 +0000 (UTC) X-FDA: 78799752780.29.A6EEE92 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf21.hostedemail.com (Postfix) with ESMTP id 14AD4D036A5E for ; Fri, 12 Nov 2021 09:28:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1636709309; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=8goeCvE6C/xkVQlONfKzUupGEa1ja4iCC9uMgoiqMPQ=; b=KtWACI9PaZ+1o6uu0KQG5meHplxXYrkX57JcrvTelhZ/g33qvRxmk946FAakbkiPeBAVd6 dyeei2Q6SVx9U7IVyXiJtjf+wuvZfoRHTip7+P9i1BRtw40LYnogU1xRAU8lGQjAmO4D6J NE1h5QNs3omPm2giEU+d1zZjm0EOi88= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-487-z9VNu_lxND2rDDvjeheNIA-1; Fri, 12 Nov 2021 04:28:24 -0500 X-MC-Unique: z9VNu_lxND2rDDvjeheNIA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D269010168C0; Fri, 12 Nov 2021 09:28:22 +0000 (UTC) Received: from t480s.redhat.com (unknown [10.39.193.225]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5613557CD2; Fri, 12 Nov 2021 09:27:51 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: David Hildenbrand , Baoquan He , Dave Young , Vivek Goyal , Andrew Morton , Philipp Rudo , kexec@lists.infradead.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: [PATCH v2] proc/vmcore: fix clearing user buffer by properly using clear_user() Date: Fri, 12 Nov 2021 10:27:50 +0100 Message-Id: <20211112092750.6921-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 14AD4D036A5E X-Stat-Signature: ipd3xsb5mn7rjtenzo1prohg7z7p5rcm Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=KtWACI9P; spf=none (imf21.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-HE-Tag: 1636709303-748824 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: To clear a user buffer we cannot simply use memset, we have to use clear_user(). With a virtio-mem device that registers a vmcore_cb and has some logically unplugged memory inside an added Linux memory block, I can easily trigger a BUG by copying the vmcore via "cp": [ 11.327580] systemd[1]: Starting Kdump Vmcore Save Service... [ 11.339697] kdump[420]: Kdump is using the default log level(3). [ 11.370964] kdump[453]: saving to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/ [ 11.373997] kdump[458]: saving vmcore-dmesg.txt to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/ [ 11.385357] kdump[465]: saving vmcore-dmesg.txt complete [ 11.386722] kdump[467]: saving vmcore [ 16.531275] BUG: unable to handle page fault for address: 00007f2374e01000 [ 16.531705] #PF: supervisor write access in kernel mode [ 16.532037] #PF: error_code(0x0003) - permissions violation [ 16.532396] PGD 7a523067 P4D 7a523067 PUD 7a528067 PMD 7a525067 PTE 800000007048f867 [ 16.532872] Oops: 0003 [#1] PREEMPT SMP NOPTI [ 16.533154] CPU: 0 PID: 468 Comm: cp Not tainted 5.15.0+ #6 [ 16.533513] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-27-g64f37cc530f1-prebuilt.qemu.org 04/01/2014 [ 16.534198] RIP: 0010:read_from_oldmem.part.0.cold+0x1d/0x86 [ 16.534552] Code: ff ff ff e8 05 ff fe ff e9 b9 e9 7f ff 48 89 de 48 c7 c7 38 3b 60 82 e8 f1 fe fe ff 83 fd 08 72 3c 49 8d 7d 08 4c 89 e9 89 e8 <49> c7 45 00 00 00 00 00 49 c7 44 05 f8 00 00 00 00 48 83 e7 f81 [ 16.535670] RSP: 0018:ffffc9000073be08 EFLAGS: 00010212 [ 16.535998] RAX: 0000000000001000 RBX: 00000000002fd000 RCX: 00007f2374e01000 [ 16.536441] RDX: 0000000000000001 RSI: 00000000ffffdfff RDI: 00007f2374e01008 [ 16.536878] RBP: 0000000000001000 R08: 0000000000000000 R09: ffffc9000073bc50 [ 16.537315] R10: ffffc9000073bc48 R11: ffffffff829461a8 R12: 000000000000f000 [ 16.537755] R13: 00007f2374e01000 R14: 0000000000000000 R15: ffff88807bd421e8 [ 16.538200] FS: 00007f2374e12140(0000) GS:ffff88807f000000(0000) knlGS:0000000000000000 [ 16.538696] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 16.539055] CR2: 00007f2374e01000 CR3: 000000007a4aa000 CR4: 0000000000350eb0 [ 16.539510] Call Trace: [ 16.539679] [ 16.539828] read_vmcore+0x236/0x2c0 [ 16.540063] ? enqueue_hrtimer+0x2f/0x80 [ 16.540323] ? inode_security+0x22/0x60 [ 16.540572] proc_reg_read+0x55/0xa0 [ 16.540807] vfs_read+0x95/0x190 [ 16.541022] ksys_read+0x4f/0xc0 [ 16.541238] do_syscall_64+0x3b/0x90 [ 16.541475] entry_SYSCALL_64_after_hwframe+0x44/0xae Some x86-64 CPUs have a CPU feature called "Supervisor Mode Access Prevention (SMAP)", which is used to detect wrong access from the kernel to user buffers like this: SMAP triggers a permissions violation on wrong access. In the x86-64 variant of clear_user(), SMAP is properly handled via clac()+stac(). To fix, properly use clear_user() when we're dealing with a user buffer. Fixes: 997c136f518c ("fs/proc/vmcore.c: add hook to read_from_oldmem() to check for non-ram pages") Acked-by: Baoquan He Cc: Dave Young Cc: Baoquan He Cc: Vivek Goyal Cc: Andrew Morton Cc: Philipp Rudo Cc: kexec@lists.infradead.org Cc: linux-mm@kvack.org Cc: linux-fsdevel@vger.kernel.org Signed-off-by: David Hildenbrand --- v1 -> v2: - Extend patch description --- fs/proc/vmcore.c | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) base-commit: debe436e77c72fcee804fb867f275e6d31aa999c diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c index 30a3b66f475a..509f85148fee 100644 --- a/fs/proc/vmcore.c +++ b/fs/proc/vmcore.c @@ -154,9 +154,13 @@ ssize_t read_from_oldmem(char *buf, size_t count, nr_bytes = count; /* If pfn is not ram, return zeros for sparse dump files */ - if (!pfn_is_ram(pfn)) - memset(buf, 0, nr_bytes); - else { + if (!pfn_is_ram(pfn)) { + tmp = 0; + if (!userbuf) + memset(buf, 0, nr_bytes); + else if (clear_user(buf, nr_bytes)) + tmp = -EFAULT; + } else { if (encrypted) tmp = copy_oldmem_page_encrypted(pfn, buf, nr_bytes, @@ -165,12 +169,12 @@ ssize_t read_from_oldmem(char *buf, size_t count, else tmp = copy_oldmem_page(pfn, buf, nr_bytes, offset, userbuf); - - if (tmp < 0) { - up_read(&vmcore_cb_rwsem); - return tmp; - } } + if (tmp < 0) { + up_read(&vmcore_cb_rwsem); + return tmp; + } + *ppos += nr_bytes; count -= nr_bytes; buf += nr_bytes;