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 631C9C433EF for ; Wed, 24 Nov 2021 20:43:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230179AbhKXUqP (ORCPT ); Wed, 24 Nov 2021 15:46:15 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:53021 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229910AbhKXUqP (ORCPT ); Wed, 24 Nov 2021 15:46:15 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1637786585; 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: in-reply-to:in-reply-to:references:references; bh=Z0zXzT0ooiXnyC6Mk1DDyA+FO3wPXXoRJHvkqQyMR5U=; b=ihA3bAyEIauaGvTXLD2bclFAdld0qMEI/cGZXOlFnLFV7aP4SxAcK9TWoaSq5BToLsgxNG W4+uN7ve6shGdbgpxiyxM6Uk+Waweq+vlGE+/hh7LhmGZRjhCtaE2PnfRQq6yMhimYMFTw /q9m+jTPD38uUBG4b5ZChrnVh7yxHSk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-305-1fHLVr6NPRmGpW-NxUYNVQ-1; Wed, 24 Nov 2021 15:43:03 -0500 X-MC-Unique: 1fHLVr6NPRmGpW-NxUYNVQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D6FF0835B58; Wed, 24 Nov 2021 20:42:57 +0000 (UTC) Received: from t480s.redhat.com (unknown [10.39.194.11]) by smtp.corp.redhat.com (Postfix) with ESMTP id 17D3926FBF; Wed, 24 Nov 2021 20:42:11 +0000 (UTC) From: David Hildenbrand To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org, akpm@linux-foundation.org, David Hildenbrand , Baoquan He , Dave Young , Vivek Goyal , Philipp Rudo Subject: [PATCH for 4.19-stable] proc/vmcore: fix clearing user buffer by properly using clear_user() Date: Wed, 24 Nov 2021 21:42:10 +0100 Message-Id: <20211124204210.26811-1-david@redhat.com> In-Reply-To: <16375840201520@kroah.com> References: <16375840201520@kroah.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org commit c1e63117711977cc4295b2ce73de29dd17066c82 upstream. 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": systemd[1]: Starting Kdump Vmcore Save Service... kdump[420]: Kdump is using the default log level(3). kdump[453]: saving to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/ kdump[458]: saving vmcore-dmesg.txt to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/ kdump[465]: saving vmcore-dmesg.txt complete kdump[467]: saving vmcore BUG: unable to handle page fault for address: 00007f2374e01000 #PF: supervisor write access in kernel mode #PF: error_code(0x0003) - permissions violation PGD 7a523067 P4D 7a523067 PUD 7a528067 PMD 7a525067 PTE 800000007048f867 Oops: 0003 [#1] PREEMPT SMP NOPTI CPU: 0 PID: 468 Comm: cp Not tainted 5.15.0+ #6 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-27-g64f37cc530f1-prebuilt.qemu.org 04/01/2014 RIP: 0010:read_from_oldmem.part.0.cold+0x1d/0x86 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 RSP: 0018:ffffc9000073be08 EFLAGS: 00010212 RAX: 0000000000001000 RBX: 00000000002fd000 RCX: 00007f2374e01000 RDX: 0000000000000001 RSI: 00000000ffffdfff RDI: 00007f2374e01008 RBP: 0000000000001000 R08: 0000000000000000 R09: ffffc9000073bc50 R10: ffffc9000073bc48 R11: ffffffff829461a8 R12: 000000000000f000 R13: 00007f2374e01000 R14: 0000000000000000 R15: ffff88807bd421e8 FS: 00007f2374e12140(0000) GS:ffff88807f000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f2374e01000 CR3: 000000007a4aa000 CR4: 0000000000350eb0 Call Trace: read_vmcore+0x236/0x2c0 proc_reg_read+0x55/0xa0 vfs_read+0x95/0x190 ksys_read+0x4f/0xc0 do_syscall_64+0x3b/0x90 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 Signed-off-by: Linus Torvalds Signed-off-by: David Hildenbrand --- fs/proc/vmcore.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c index c4147e50af98..f5dfedc01552 100644 --- a/fs/proc/vmcore.c +++ b/fs/proc/vmcore.c @@ -117,14 +117,19 @@ static 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) == 0) - memset(buf, 0, nr_bytes); - else { + if (pfn_is_ram(pfn) == 0) { + tmp = 0; + if (!userbuf) + memset(buf, 0, nr_bytes); + else if (clear_user(buf, nr_bytes)) + tmp = -EFAULT; + } else { tmp = copy_oldmem_page(pfn, buf, nr_bytes, offset, userbuf); - if (tmp < 0) - return tmp; } + if (tmp < 0) + return tmp; + *ppos += nr_bytes; count -= nr_bytes; buf += nr_bytes; -- 2.31.1