From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id 79B506B0350 for ; Thu, 1 Jun 2017 12:58:17 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id 62so49385678pft.3 for ; Thu, 01 Jun 2017 09:58:17 -0700 (PDT) Received: from EUR03-DB5-obe.outbound.protection.outlook.com (mail-eopbgr40125.outbound.protection.outlook.com. [40.107.4.125]) by mx.google.com with ESMTPS id c22si35424823plk.79.2017.06.01.09.58.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 01 Jun 2017 09:58:16 -0700 (PDT) Subject: Re: [PATCH 3/4] arm64/kasan: don't allocate extra shadow memory References: <20170601162338.23540-1-aryabinin@virtuozzo.com> <20170601162338.23540-3-aryabinin@virtuozzo.com> <20170601163442.GC17711@leverpostej> <20170601165205.GA8191@leverpostej> <75ea368f-9268-44fd-f3f6-2a48dc8d2fe8@virtuozzo.com> From: Andrey Ryabinin Message-ID: <31a41822-35e1-1b4a-09f7-0a99571ee89a@virtuozzo.com> Date: Thu, 1 Jun 2017 20:00:09 +0300 MIME-Version: 1.0 In-Reply-To: <75ea368f-9268-44fd-f3f6-2a48dc8d2fe8@virtuozzo.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mark Rutland , Dmitry Vyukov Cc: Andrew Morton , Catalin Marinas , Will Deacon , LKML , kasan-dev , "linux-mm@kvack.org" , Alexander Potapenko , linux-arm-kernel@lists.infradead.org On 06/01/2017 07:59 PM, Andrey Ryabinin wrote: > > > On 06/01/2017 07:52 PM, Mark Rutland wrote: >> On Thu, Jun 01, 2017 at 06:45:32PM +0200, Dmitry Vyukov wrote: >>> On Thu, Jun 1, 2017 at 6:34 PM, Mark Rutland wrote: >>>> On Thu, Jun 01, 2017 at 07:23:37PM +0300, Andrey Ryabinin wrote: >>>>> We used to read several bytes of the shadow memory in advance. >>>>> Therefore additional shadow memory mapped to prevent crash if >>>>> speculative load would happen near the end of the mapped shadow memory. >>>>> >>>>> Now we don't have such speculative loads, so we no longer need to map >>>>> additional shadow memory. >>>> >>>> I see that patch 1 fixed up the Linux helpers for outline >>>> instrumentation. >>>> >>>> Just to check, is it also true that the inline instrumentation never >>>> performs unaligned accesses to the shadow memory? >>> > > Correct, inline instrumentation assumes that all accesses are properly aligned as it > required by C standard. I knew that the kernel violates this rule in many places, > therefore I decided to add checks for unaligned accesses in outline case. > > >>> Inline instrumentation generally accesses only a single byte. >> >> Sorry to be a little pedantic, but does that mean we'll never access the >> additional shadow, or does that mean it's very unlikely that we will? >> >> I'm guessing/hoping it's the former! >> > > Outline will never access additional shadow byte: https://github.com/google/sanitizers/wiki/AddressSanitizerAlgorithm#unaligned-accesses s/Outline/inline of course. > >> Thanks, >> Mark. >> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org