From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751271AbeECX07 (ORCPT ); Thu, 3 May 2018 19:26:59 -0400 Received: from vps-vb.mhejs.net ([37.28.154.113]:38310 "EHLO vps-vb.mhejs.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750965AbeECX0z (ORCPT ); Thu, 3 May 2018 19:26:55 -0400 Subject: Re: [PATCH v5 4/6] x86/microcode/AMD: Check microcode container data in the late loader To: Borislav Petkov Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org References: <8f204a953dc4b46477e214ebd291021d7ab6fa6c.1524515406.git.mail@maciej.szmigiero.name> <20180430090527.GC6509@pd.tnic> <20180501084317.GC31863@pd.tnic> <20180501200308.GC13171@pd.tnic> <9cf234e8-4d96-46f0-70e0-7d60d49671d8@maciej.szmigiero.name> <20180503100133.GB20023@pd.tnic> From: "Maciej S. Szmigiero" Message-ID: <756e5bd8-6cd8-5f28-6cab-c60396dc5de4@maciej.szmigiero.name> Date: Fri, 4 May 2018 01:26:50 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180503100133.GB20023@pd.tnic> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03.05.2018 12:01, Borislav Petkov wrote: > On Wed, May 02, 2018 at 02:47:39AM +0200, Maciej S. Szmigiero wrote: >> On 01.05.2018 22:03, Borislav Petkov wrote: >>> On Tue, May 01, 2018 at 06:19:56PM +0200, Maciej S. Szmigiero wrote: >>>> -EINVAL cast to unsigned int is 4294967274 and this value is also >>>> a valid count of bytes to skip that this function can return. >>> >>> And where exactly in the *old* code do we do that? >> >> The old code returned this value as a signed int, but then any >> "patch_size" value (which is u32) above INT_MAX read from a section header >> wrapped around to a negative pseudo-error code (which likely didn't match >> any actual error number). > > Lemme repeat my question: *where* *exactly* in the old code do we do that? > > Feel free to paste snippets to show what you mean. > >>From verify_and_add_patch(): > static int verify_and_add_patch(u8 family, u8 *fw, unsigned int leftover) > { > struct microcode_header_amd *mc_hdr; > struct ucode_patch *patch; > unsigned int patch_size, crnt_size, ret; > u32 proc_fam; > u16 proc_id; > > patch_size = *(u32 *)(fw + 4); Here we read a u32 (= unsigned int) value from a section header and store it into an unsigned int variable. > crnt_size = patch_size + SECTION_HDR_SIZE; Here we add 8 (SECTION_HDR_SIZE) to this value and once again store it into an unsigned int variable. > mc_hdr = (struct microcode_header_amd *)(fw + SECTION_HDR_SIZE); > proc_id = mc_hdr->processor_rev_id; > > proc_fam = find_cpu_family_by_equiv_cpu(proc_id); > if (!proc_fam) { > pr_err("No patch family for equiv ID: 0x%04x\n", proc_id); > return crnt_size; Here we return this variable, implicitly converting it into a (signed) int. Any value above INT_MAX will wrap around to a negative pseudo-error code (which might not match any actual error number). Maciej