From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751527AbdGRN5R (ORCPT ); Tue, 18 Jul 2017 09:57:17 -0400 Received: from mail-cys01nam02on0051.outbound.protection.outlook.com ([104.47.37.51]:6896 "EHLO NAM02-CY1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751409AbdGRN5N (ORCPT ); Tue, 18 Jul 2017 09:57:13 -0400 Authentication-Results: amd.com; dkim=none (message not signed) header.d=none;amd.com; dmarc=none action=none header.from=amd.com; Subject: Re: [PATCH v10 37/38] compiler-gcc.h: Introduce __nostackp function attribute To: Ingo Molnar Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-efi@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org, kasan-dev@googlegroups.com, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Arnd Bergmann , Jonathan Corbet , Matt Fleming , Konrad Rzeszutek Wilk , Andrey Ryabinin , Ingo Molnar , Borislav Petkov , Andy Lutomirski , "H. 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Tsirkin" , Brijesh Singh References: <0576fd5c74440ad0250f16ac6609ecf587812456.1500319216.git.thomas.lendacky@amd.com> <20170718093631.pnamvdrkmzcjz64j@gmail.com> From: Tom Lendacky Message-ID: Date: Tue, 18 Jul 2017 08:56:56 -0500 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20170718093631.pnamvdrkmzcjz64j@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [165.204.78.1] X-ClientProxiedBy: BN6PR14CA0047.namprd14.prod.outlook.com (10.171.172.161) To DM5PR12MB1145.namprd12.prod.outlook.com (10.168.236.140) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: ef9d289a-4250-4d65-90e1-08d4cde4e11a X-MS-Office365-Filtering-HT: Tenant X-Microsoft-Antispam: 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1;DM5PR12MB1145;20:Jn8csX6g0hEpqN/vjZMHpD9DksIJX9kLmN4MTwnu1qgBIx7317vZIQ7W73pSHugs8OinbiiJLzj6gIa17VFQzQRxvcKjtaFVIT6ZmB4hBFOFnswcA67J8jwu8EUBcYou5YTFUBkSt2k7iheC/zsL06hFtJFhEug5F2P1lfjoqd7oj6i1IbL5/5oAOwA/z8fudraWUhiHnQM6SG+hZ1vYUku0KVHG6oJ3QVZzYcv5vMt+TxSQsxgdEg3THQsn4zcO X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Jul 2017 13:57:05.3032 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR12MB1145 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/18/2017 4:36 AM, Ingo Molnar wrote: > > * Tom Lendacky wrote: > >> Create a new function attribute, __nostackp, that can used to turn off >> stack protection on a per function basis. >> >> Signed-off-by: Tom Lendacky >> --- >> include/linux/compiler-gcc.h | 2 ++ >> include/linux/compiler.h | 4 ++++ >> 2 files changed, 6 insertions(+) >> >> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h >> index cd4bbe8..682063b 100644 >> --- a/include/linux/compiler-gcc.h >> +++ b/include/linux/compiler-gcc.h >> @@ -166,6 +166,8 @@ >> >> #if GCC_VERSION >= 40100 >> # define __compiletime_object_size(obj) __builtin_object_size(obj, 0) >> + >> +#define __nostackp __attribute__((__optimize__("no-stack-protector"))) >> #endif >> >> #if GCC_VERSION >= 40300 >> diff --git a/include/linux/compiler.h b/include/linux/compiler.h >> index 219f82f..63cbca1 100644 >> --- a/include/linux/compiler.h >> +++ b/include/linux/compiler.h >> @@ -470,6 +470,10 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s >> #define __visible >> #endif >> >> +#ifndef __nostackp >> +#define __nostackp >> +#endif > > So I changed this from the hard to read and ambiguous "__nostackp" abbreviation > (does it mean 'no stack pointer?') to "__nostackprotector", plus added this detail > to the changelog: > > | ( This is needed by the SME in-place kernel memory encryption feature, > | which activates encryption in its sme_enable() function and thus changes the > | visible value of the stack protection cookie on function return. ) > > Agreed? Hi Ingo, I debugged this to needing "__nostackprotector" because sme_enable() is called very early in the boot process before everything is properly setup to fully support stack protection when KASLR is enabled. Without this attribute the call to sme_enable() would fail even if encryption was disabled with the "mem_encrypt=off" command line option. If KASLR wasn't enabled, then everything worked fine without the "__nostackprotector" attribute, encryption enabled or not. The stack protection support is activated because of the 16-byte character buffer in the sme_enable() routine. I think we'll find that if a character buffer greater than 8 bytes is added to, for example, __startup_64, then this attribute will need to be added to that routine. Thanks, Tom > > Thanks, > > Ingo >