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 5EA28C433F5 for ; Mon, 23 May 2022 17:15:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240014AbiEWRPk (ORCPT ); Mon, 23 May 2022 13:15:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34862 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240502AbiEWRM3 (ORCPT ); Mon, 23 May 2022 13:12:29 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8B0C96212E; Mon, 23 May 2022 10:11:40 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 1C7DCB81210; Mon, 23 May 2022 17:11:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7C65AC385A9; Mon, 23 May 2022 17:11:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1653325898; bh=TdT7f4/YK9v3b4c8MVCNKjiB6pt1Yf0Yg24yCYQbA3I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=AX72BvuFWp+EMV46MSxfSjKSaVHHfmb4gsQ8YQGfTyVmT4qxuX3WusRjYCYzzOYhM I8WQb1tRhgERdBspja8p3B0WxwGOUv4a0Uu+Rf2CtlmvT4IUE5aNy0ZWTvsudwd7RE UeGPChOcgSPG6p0GX/4xJMAD0JVRA2fE4GpDt/xE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Halil Pasic , Christoph Hellwig , Ovidiu Panait Subject: [PATCH 4.19 42/44] swiotlb: fix info leak with DMA_FROM_DEVICE Date: Mon, 23 May 2022 19:05:26 +0200 Message-Id: <20220523165800.988772511@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220523165752.797318097@linuxfoundation.org> References: <20220523165752.797318097@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Halil Pasic commit ddbd89deb7d32b1fbb879f48d68fda1a8ac58e8e upstream. The problem I'm addressing was discovered by the LTP test covering cve-2018-1000204. A short description of what happens follows: 1) The test case issues a command code 00 (TEST UNIT READY) via the SG_IO interface with: dxfer_len == 524288, dxdfer_dir == SG_DXFER_FROM_DEV and a corresponding dxferp. The peculiar thing about this is that TUR is not reading from the device. 2) In sg_start_req() the invocation of blk_rq_map_user() effectively bounces the user-space buffer. As if the device was to transfer into it. Since commit a45b599ad808 ("scsi: sg: allocate with __GFP_ZERO in sg_build_indirect()") we make sure this first bounce buffer is allocated with GFP_ZERO. 3) For the rest of the story we keep ignoring that we have a TUR, so the device won't touch the buffer we prepare as if the we had a DMA_FROM_DEVICE type of situation. My setup uses a virtio-scsi device and the buffer allocated by SG is mapped by the function virtqueue_add_split() which uses DMA_FROM_DEVICE for the "in" sgs (here scatter-gather and not scsi generics). This mapping involves bouncing via the swiotlb (we need swiotlb to do virtio in protected guest like s390 Secure Execution, or AMD SEV). 4) When the SCSI TUR is done, we first copy back the content of the second (that is swiotlb) bounce buffer (which most likely contains some previous IO data), to the first bounce buffer, which contains all zeros. Then we copy back the content of the first bounce buffer to the user-space buffer. 5) The test case detects that the buffer, which it zero-initialized, ain't all zeros and fails. One can argue that this is an swiotlb problem, because without swiotlb we leak all zeros, and the swiotlb should be transparent in a sense that it does not affect the outcome (if all other participants are well behaved). Copying the content of the original buffer into the swiotlb buffer is the only way I can think of to make swiotlb transparent in such scenarios. So let's do just that if in doubt, but allow the driver to tell us that the whole mapped buffer is going to be overwritten, in which case we can preserve the old behavior and avoid the performance impact of the extra bounce. Signed-off-by: Halil Pasic Signed-off-by: Christoph Hellwig [OP: backport to 4.19: adjusted context] Signed-off-by: Ovidiu Panait Signed-off-by: Greg Kroah-Hartman --- Documentation/DMA-attributes.txt | 10 ++++++++++ include/linux/dma-mapping.h | 8 ++++++++ kernel/dma/swiotlb.c | 3 ++- 3 files changed, 20 insertions(+), 1 deletion(-) --- a/Documentation/DMA-attributes.txt +++ b/Documentation/DMA-attributes.txt @@ -156,3 +156,13 @@ accesses to DMA buffers in both privileg subsystem that the buffer is fully accessible at the elevated privilege level (and ideally inaccessible or at least read-only at the lesser-privileged levels). + +DMA_ATTR_PRIVILEGED +------------------- + +Some advanced peripherals such as remote processors and GPUs perform +accesses to DMA buffers in both privileged "supervisor" and unprivileged +"user" modes. This attribute is used to indicate to the DMA-mapping +subsystem that the buffer is fully accessible at the elevated privilege +level (and ideally inaccessible or at least read-only at the +lesser-privileged levels). --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -71,6 +71,14 @@ #define DMA_ATTR_PRIVILEGED (1UL << 9) /* + * This is a hint to the DMA-mapping subsystem that the device is expected + * to overwrite the entire mapped size, thus the caller does not require any + * of the previous buffer contents to be preserved. This allows + * bounce-buffering implementations to optimise DMA_FROM_DEVICE transfers. + */ +#define DMA_ATTR_OVERWRITE (1UL << 10) + +/* * A dma_addr_t can hold any valid DMA or bus address for the platform. * It can be given to a device to use as a DMA source or target. A CPU cannot * reference a dma_addr_t directly because there may be translation between --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -588,7 +588,8 @@ found: for (i = 0; i < nslots; i++) io_tlb_orig_addr[index+i] = orig_addr + (i << IO_TLB_SHIFT); if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) && - (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)) + (!(attrs & DMA_ATTR_OVERWRITE) || dir == DMA_TO_DEVICE || + dir == DMA_BIDIRECTIONAL)) swiotlb_bounce(orig_addr, tlb_addr, size, DMA_TO_DEVICE); return tlb_addr;