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 X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0BA08C433DB for ; Tue, 30 Mar 2021 23:32:12 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 015D5619B1 for ; Tue, 30 Mar 2021 23:32:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 015D5619B1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=bugs.launchpad.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:39324 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lRNqD-0005p0-PC for qemu-devel@archiver.kernel.org; Tue, 30 Mar 2021 19:32:09 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53350) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lRNow-00056A-Qk for qemu-devel@nongnu.org; Tue, 30 Mar 2021 19:30:50 -0400 Received: from indium.canonical.com ([91.189.90.7]:54144) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1lRNot-0004FB-3b for qemu-devel@nongnu.org; Tue, 30 Mar 2021 19:30:50 -0400 Received: from loganberry.canonical.com ([91.189.90.37]) by indium.canonical.com with esmtp (Exim 4.86_2 #2 (Debian)) id 1lRNoq-0007I2-2s for ; Tue, 30 Mar 2021 23:30:44 +0000 Received: from loganberry.canonical.com (localhost [127.0.0.1]) by loganberry.canonical.com (Postfix) with ESMTP id 07E632E8165 for ; Tue, 30 Mar 2021 23:30:44 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Date: Tue, 30 Mar 2021 23:22:03 -0000 From: Richard Henderson <1921948@bugs.launchpad.net> To: qemu-devel@nongnu.org X-Launchpad-Notification-Type: bug X-Launchpad-Bug: product=qemu; status=New; importance=Undecided; assignee=rth@twiddle.net; X-Launchpad-Bug-Information-Type: Public X-Launchpad-Bug-Private: no X-Launchpad-Bug-Security-Vulnerability: no X-Launchpad-Bug-Commenters: rth xairy X-Launchpad-Bug-Reporter: Andrey Konovalov (xairy) X-Launchpad-Bug-Modifier: Richard Henderson (rth) References: <161713286145.25906.15042270704525675392.malonedeb@wampee.canonical.com> Message-Id: <161714652343.360.6742694661379399744.malone@soybean.canonical.com> Subject: [Bug 1921948] Re: MTE tags not checked properly for unaligned accesses at EL1 X-Launchpad-Message-Rationale: Subscriber (QEMU) @qemu-devel-ml X-Launchpad-Message-For: qemu-devel-ml Precedence: bulk X-Generated-By: Launchpad (canonical.com); Revision="21fefc602783aa4ba863a4a6c29d38d788ce04ad"; Instance="production" X-Launchpad-Hash: 6facc559c51d01f97148d1d853743810f0a83310 Received-SPF: none client-ip=91.189.90.7; envelope-from=bounces@canonical.com; helo=indium.canonical.com X-Spam_score_int: -65 X-Spam_score: -6.6 X-Spam_bar: ------ X-Spam_report: (-6.6 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.249, RCVD_IN_DNSWL_HI=-5, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Bug 1921948 <1921948@bugs.launchpad.net> Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" I believe that you're correct, and that I mis-read the MTE specification. I believed that exactly one mte tag check was made for any single memory access. But I missed that unaligned accesses are as-if a sequence of byte accesses -- in the Arm ARM, see aarch64/functions/memory/Mem[]. I'm still trying to verify this via the Arm FVP, but so far I've not found the right incantation of parameters to properly enable MTE. (I can enable the instructions, but a simple stg/ldg test suggests that there is no tag storage enabled -- all tags read as 0.) ** Changed in: qemu Assignee: (unassigned) =3D> Richard Henderson (rth) -- = You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1921948 Title: MTE tags not checked properly for unaligned accesses at EL1 Status in QEMU: New Bug description: For kernel memory accesses that span across two memory granules, QEMU's MTE implementation only checks the tag of the first granule but not of the second one. To reproduce this, build the Linux kernel with CONFIG_KASAN_HW_TAGS enabled, apply the patch below, and boot the kernel: diff --git a/sound/last.c b/sound/last.c index f0bb98780e70..04745cb30b74 100644 --- a/sound/last.c +++ b/sound/last.c @@ -5,12 +5,18 @@ */ = #include +#include #include = static int __init alsa_sound_last_init(void) { struct snd_card *card; int idx, ok =3D 0; + + char *ptr =3D kmalloc(128, GFP_KERNEL); + pr_err("KASAN report should follow:\n"); + *(volatile unsigned long *)(ptr + 124); + kfree(ptr); = printk(KERN_INFO "ALSA device list:\n"); for (idx =3D 0; idx < SNDRV_CARDS; idx++) { KASAN tags the 128 allocated bytes with the same tag as the returned pointer. The memory granule that follows the 128 allocated bytes has a different tag (with 1/15 probability). Expected result: a tag fault is detected and a KASAN report is printed wh= en accessing bytes [124, 130). Observed result: no tag fault is detected and no KASAN report is printed. Here are the flags that I use to run QEMU if they matter: qemu-system-aarch64 -s -machine virt,mte=3Don -cpu max -m 2G -smp 2 -net user,host=3D10.0.2.10,hostfwd=3Dtcp:127.0.0.1:10021-:22 -net nic -nographic -kernel ./Image -append "console=3DttyAMA0 root=3D/dev/vda earlyprintk=3Dserial" -drive file=3D./fs.img,format=3Draw,if=3Dvirtio -no- shutdown -no-reboot To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1921948/+subscriptions