From patchwork Sat Nov 20 00:43:58 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 12629943 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 48D7BC433EF for ; Sat, 20 Nov 2021 00:51:20 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B442C6B0088; Fri, 19 Nov 2021 19:44:10 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id AF3726B0089; Fri, 19 Nov 2021 19:44:10 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9E38D6B008A; Fri, 19 Nov 2021 19:44:10 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0097.hostedemail.com [216.40.44.97]) by kanga.kvack.org (Postfix) with ESMTP id 9094C6B0088 for ; Fri, 19 Nov 2021 19:44:10 -0500 (EST) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 5B2188CE3F for ; Sat, 20 Nov 2021 00:44:00 +0000 (UTC) X-FDA: 78827461440.29.613827E Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf31.hostedemail.com (Postfix) with ESMTP id 3520E1052983 for ; Sat, 20 Nov 2021 00:43:57 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 0170D61A86; Sat, 20 Nov 2021 00:43:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1637369039; bh=UAr7Q/5h2/Uck3swGjAInJ+tTo4aGlSu0RjHHUlzxoc=; h=Date:From:To:Subject:In-Reply-To:From; b=pAhzlG9e76LG6n4GOP7TuNPBssnGg9LtoOogVr1N7Y0dG/tEGq/JnTIg6Y7VKRn2s BjZY+PZkSCULBq+TxnIyOLjxleGl7xwXuqDTxPmzuJadgEllS3WImWf7yBrHL6EiFH 85GEolhuIWImeaXAwZxBlkr2oHErR/6yAWHqFStQ= Date: Fri, 19 Nov 2021 16:43:58 -0800 From: Andrew Morton To: akpm@linux-foundation.org, bhe@redhat.com, david@redhat.com, dyoung@redhat.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, prudo@redhat.com, stable@vger.kernel.org, torvalds@linux-foundation.org, vgoyal@redhat.com Subject: [patch 15/15] proc/vmcore: fix clearing user buffer by properly using clear_user() Message-ID: <20211120004358.K3wyLJN5Y%akpm@linux-foundation.org> In-Reply-To: <20211119164248.50feee07c5d2cc6cc4addf97@linux-foundation.org> User-Agent: s-nail v14.8.16 X-Stat-Signature: gufnkib4iis1i3qyu839gukzaedngzc7 Authentication-Results: imf31.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=pAhzlG9e; dmarc=none; spf=pass (imf31.hostedemail.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 3520E1052983 X-HE-Tag: 1637369037-438609 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: From: David Hildenbrand Subject: proc/vmcore: fix clearing user buffer by properly using clear_user() 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. Link: https://lkml.kernel.org/r/20211112092750.6921-1-david@redhat.com Fixes: 997c136f518c ("fs/proc/vmcore.c: add hook to read_from_oldmem() to check for non-ram pages") Signed-off-by: David Hildenbrand Acked-by: Baoquan He Cc: Dave Young Cc: Baoquan He Cc: Vivek Goyal Cc: Philipp Rudo Cc: Signed-off-by: Andrew Morton --- fs/proc/vmcore.c | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) --- a/fs/proc/vmcore.c~proc-vmcore-fix-clearing-user-buffer-by-properly-using-clear_user +++ a/fs/proc/vmcore.c @@ -154,9 +154,13 @@ ssize_t read_from_oldmem(char *buf, size 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 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;