From patchwork Mon Aug 7 19:07:33 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 13344755 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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 60B8DC001DE for ; Mon, 7 Aug 2023 19:08:54 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qT5a1-0003ib-0E; Mon, 07 Aug 2023 15:07:49 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qT5Zy-0003hk-Rl for qemu-devel@nongnu.org; Mon, 07 Aug 2023 15:07:46 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qT5Zx-0005o0-GD for qemu-devel@nongnu.org; Mon, 07 Aug 2023 15:07:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1691435264; 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=8/JG4xq1fn1DPP8n2T9g6mLn79wHbUIsLvpRXYT889c=; b=K05oPt84vZBr+c0IOHa/EAUamwoZjZHQpkTBI6JL464i2rsuWiswAbmp9CJ2S6NjEwgZ0I Pqvys6SJFeOv8CkDDI4wkzaTKTz0aRRJGVOMqeqKQpIxG1PBc8btmAkUIylu/o73ySw/Ac augYjAnZWxe3ttT+HxBAIrEV/YyW/fQ= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-653-ENfz1GifPdqnYS8JGhrKtw-1; Mon, 07 Aug 2023 15:07:43 -0400 X-MC-Unique: ENfz1GifPdqnYS8JGhrKtw-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 94E6980523D; Mon, 7 Aug 2023 19:07:42 +0000 (UTC) Received: from t14s.redhat.com (unknown [10.39.192.170]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2F891403166; Mon, 7 Aug 2023 19:07:41 +0000 (UTC) From: David Hildenbrand To: qemu-devel@nongnu.org Cc: David Hildenbrand , Paolo Bonzini , Peter Xu , Igor Mammedov , Thiner Logoer , =?utf-8?q?Philippe_Mathieu-Daud?= =?utf-8?q?=C3=A9?= Subject: [PATCH v1 2/3] softmmu/physmem: fail creation of new files in file_ram_open() with readonly=true Date: Mon, 7 Aug 2023 21:07:33 +0200 Message-ID: <20230807190736.572665-3-david@redhat.com> In-Reply-To: <20230807190736.572665-1-david@redhat.com> References: <20230807190736.572665-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 Received-SPF: pass client-ip=170.10.129.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Currently, if a file does not exist yet, file_ram_open() will create new empty file and open it writable. However, it even does that when readonly=true was specified. So instead of opening the file read-only, we'll open it writable, implying that later fallocate() or ftruncate() could succeed. Specifying O_RDONLY instead would theoretically work, however, ftruncate() will refuse to resize the new empty file and we'll get a warning: ftruncate: Invalid argument mmap() will succeed, but any later access to that memory would fail with SIGBUS. Undesirable. If someone intends to let QEMU open+mmap a file read-only, better create+resize+fill that file ahead of time outside of QEMU context. We'll now fail with: ./qemu-system-x86_64 \ -object memory-backend-file,id=ram0,mem-path=tmp/ls,readonly=true,size=1g qemu-system-x86_64: can't open backing store tmp/ls for guest RAM: No such file or directory It's unlikely that this will harm existing users: especially R/O NVDIMMs better expose some reasonable data that already exists. Everything else would just hide user errors when accidentally specifying a non-existent file. Note that the only memory-backend-file will end up calling memory_region_init_ram_from_file() -> qemu_ram_alloc_from_file() -> file_ram_open(). Signed-off-by: David Hildenbrand --- softmmu/physmem.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/softmmu/physmem.c b/softmmu/physmem.c index d1ae694b20..9580567608 100644 --- a/softmmu/physmem.c +++ b/softmmu/physmem.c @@ -1304,6 +1304,13 @@ static int file_ram_open(const char *path, break; } if (errno == ENOENT) { + if (readonly) { + /* + * O_RDONLY would later make ftruncate() fail, leading to + * SIGBUS after mmap(). + */ + return -ENOENT; + } /* @path names a file that doesn't exist, create it */ fd = open(path, O_RDWR | O_CREAT | O_EXCL, 0644); if (fd >= 0) {