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 AAF8BC4332F for ; Tue, 25 Jan 2022 17:09:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241462AbiAYRJQ (ORCPT ); Tue, 25 Jan 2022 12:09:16 -0500 Received: from foss.arm.com ([217.140.110.172]:56628 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353604AbiAYRHg (ORCPT ); Tue, 25 Jan 2022 12:07:36 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 892521FB; Tue, 25 Jan 2022 09:07:33 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.1.45]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1C3133F766; Tue, 25 Jan 2022 09:07:31 -0800 (PST) Date: Tue, 25 Jan 2022 17:07:29 +0000 From: Mark Rutland To: Evgenii Stepanov Cc: Catalin Marinas , Will Deacon , Ard Biesheuvel , Robin Murphy , Jisheng Zhang , Linux ARM , LKML Subject: Re: [PATCH] arm64: extable: fix null deref in load_unaligned_zeropad. Message-ID: References: <20220122023447.1480995-1-eugenis@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 25, 2022 at 08:59:07AM -0800, Evgenii Stepanov wrote: > On Tue, Jan 25, 2022 at 7:50 AM Mark Rutland wrote: > > > > On Tue, Jan 25, 2022 at 03:23:20PM +0000, Mark Rutland wrote: > > > On Fri, Jan 21, 2022 at 06:34:47PM -0800, Evgenii Stepanov wrote: > > > > ex_handler_load_unaligned_zeropad extracts the source and data register > > > > numbers from the wrong field of the exception table. > > > > > > Ouch. Did you find this by inspection, or did this show up in testing? > > > > > > Sorry about this. > > > > > > I think we should be a little more explicit as to exactly what goes wrong. How > > > about: > > > > > > | In ex_handler_load_unaligned_zeropad() we erroneously extract the data and > > > | addr register indices from ex->type rather than ex->data. As ex->type will > > > | contain EX_TYPE_LOAD_UNALIGNED_ZEROPAD (i.e. 4): > > > | > > > | * We'll always treat X0 as the address register, since EX_DATA_REG_ADDR is > > > | extracted from bits [9:5]. Thus, we may attempt to dereference an arbitrary > > > | address as X0 may hold an arbitary value. > > > | > > > | * We'll always treat X4 as the data register, since EX_DATA_REG_DATA is > > > | extracted from bits [4:0]. Thus we will corrupt X4 and cause arbitrary > > > | behaviour within load_unaligned_zeropad() and its caller. > > > | > > > | Fix this by extracting both values from ex->data as originally intended. > > > > > > > Fixes: 753b3236 > > > > > > That should be expanded, e.g. > > > > > > Fixes: 753b32368705c396 ("arm64: extable: add load_unaligned_zeropad() handler") > > > > > > With those changes: > > > > > > Reviewed-by: Mark Rutland > > > > Looking again, sicne this isn't jsut a null-deref, can we also rework the > > title, something like: > > > > | arm64: extable: fix load_unaligned_zeropad() reg indices > > That's a much better commit message, thank you! I'll upload v2 shortly. > > This was found by updating to a newer QEMU that correctly delivers MTE > faults from unaligned memory accesses, and triggers this bug reliably > during Android boot. I'll add a stack trace to v2. That'd be great, thanks! Mark.