Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932263AbcJMNLK (ORCPT ); Thu, 13 Oct 2016 09:11:10 -0400 Received: from mail-qk0-f194.google.com ([209.85.220.194]:33987 "EHLO mail-qk0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932234AbcJMNK7 (ORCPT ); Thu, 13 Oct 2016 09:10:59 -0400 MIME-Version: 1.0 In-Reply-To: <1473423687-4889-1-git-send-email-yu.c.chen@intel.com> References: <1473423687-4889-1-git-send-email-yu.c.chen@intel.com> From: Denys Vlasenko Date: Thu, 13 Oct 2016 15:10:18 +0200 Message-ID: Subject: Re: [PATCH][v10] PM / hibernate: Verify the consistent of e820 memory map by md5 digest To: Chen Yu Cc: linux-pm@vger.kernel.org, X86 ML , Linux Kernel Mailing List , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "Rafael J . Wysocki" , Pavel Machek , Lee Chun-Yi , Borislav Petkov Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3759 Lines: 99 On Fri, Sep 9, 2016 at 2:21 PM, Chen Yu wrote: > On some platforms, there is occasional panic triggered when trying to > resume from hibernation, a typical panic looks like: > > "BUG: unable to handle kernel paging request at ffff880085894000 > IP: [] load_image_lzo+0x8c2/0xe70" > > Investigation carried out by Lee Chun-Yi show that this is because > e820 map has been changed by BIOS across hibernation, and one > of the page frames from suspend kernel is right located in restore > kernel's unmapped region, so panic comes out when accessing unmapped > kernel address. > > In order to expose this issue earlier, the md5 hash of e820 map > is passed from suspend kernel to restore kernel, and the restore > kernel will terminate the resume process once it finds the md5 > hash are not the same. > > As the format of image header has been modified, the magic number > should also be adjusted as kernels with the same RESTORE_MAGIC have > to use the same header format and interpret all of the fields in > it in the same way. > > If the suspend kernel is built without md5 support, and the restore > kernel has md5 support, then the latter will bypass the check process. > Vice versa the restore kernel will bypass the check if it does not > support md5 operation. > > Note: > 1. Without this patch applied, it is possible that BIOS has > provided an inconsistent memory map, but the resume kernel is still > able to restore the image anyway(e.g, E820_RAM region is the superset > of the previous one), although the system might be unstable. So this > patch tries to treat any inconsistent e820 as illegal. > > 2. Another case is, this patch replies on comparing the e820_saved, but > currently the e820_save might not be strictly the same across > hibernation, even if BIOS has provided consistent e820 map - In > theory mptable might modify the BIOS-provided e820_saved dynamically > in early_reserve_e820_mpc_new, which would allocate a buffer from > E820_RAM, and marks it from E820_RAM to E820_RESERVED). > This is a potential and rare case we need to deal with in OS in > the future. > > Suggested-by: Pavel Machek > Suggested-by: Rafael J. Wysocki > Cc: Rafael J. Wysocki > Cc: Pavel Machek > Cc: Lee Chun-Yi > Cc: Borislav Petkov > Acked-by: Pavel Machek > Signed-off-by: Chen Yu > --- > +static int get_e820_md5(struct e820map *map, void *buf) > +{ > + struct scatterlist sg; > + struct crypto_ahash *tfm; > + struct ahash_request *req; > + int ret = 0; > + > + tfm = crypto_alloc_ahash("md5", 0, CRYPTO_ALG_ASYNC); > + if (IS_ERR(tfm)) > + return -ENOMEM; > + > + req = ahash_request_alloc(tfm, GFP_KERNEL); > + if (!req) { > + ret = -ENOMEM; > + goto free_ahash; > + } I looked elsewhere in kernel, and there is this idiom for placing struct ahash_request on stack. Instead of the ahash_request_alloc() and never-actually-tirggering-error handling, you can do: { AHASH_REQUEST_ON_STACK(req, tfm); > + > + sg_init_one(&sg, (u8 *)map, sizeof(struct e820map)); > + ahash_request_set_callback(req, 0, NULL, NULL); > + ahash_request_set_crypt(req, &sg, buf, sizeof(struct e820map)); > + > + if (crypto_ahash_digest(req)) > + ret = -EINVAL; > + > + ahash_request_free(req); > + free_ahash: and, naturally, the free() and the label would not be needed too, just close the one extra brace: > + crypto_free_ahash(tfm); > + > + return ret; } > +}