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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 BBFECC433F5 for ; Tue, 25 Jan 2022 17:08:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=4oOaB73wExwZYMnrtISVCZrmR05E2lSuuEsLHkH4rms=; b=zOt5aUAZLshWBt ob7GaSGryfjbiZwkbZsEOMd/uln6xQBFWmLpNEX/aSnTjzRhu4gWQjfW58llwJ5RkamDsseHK0jL/ 3CsKihH7DMyRIqe/Xbu4HKR9pMptYsS1TJaJCQIL/DHj++QwHkdN+oVDNZrbYL/YwPmHb15K0Hbo8 diPLz1ID75ie4UaCc4qrNf6IPN3+KfjLwL95ojP6DB5eoJqN5gXfhXRG0IQAvhKfAkdCkgSme6JJP u1NsKaDbk8w7gw0aveaTy0HNn8ovqbB/WugmvSyrIKXdaQBmFNqzoOkj5YHKDV5296afA3I9NiBqb svzU4VAhYSlzzXoJvEGw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nCPIH-008s1R-CO; Tue, 25 Jan 2022 17:07:45 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nCPI7-008rz7-3n for linux-arm-kernel@lists.infradead.org; Tue, 25 Jan 2022 17:07:36 +0000 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-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220125_090735_233944_75696F88 X-CRM114-Status: GOOD ( 21.88 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel