From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id 3540D6B0315 for ; Thu, 1 Jun 2017 12:57:28 -0400 (EDT) Received: by mail-pf0-f197.google.com with SMTP id n75so49394387pfh.0 for ; Thu, 01 Jun 2017 09:57:28 -0700 (PDT) Received: from EUR01-HE1-obe.outbound.protection.outlook.com (mail-he1eur01on0107.outbound.protection.outlook.com. [104.47.0.107]) by mx.google.com with ESMTPS id k184si19728711pgd.390.2017.06.01.09.57.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 01 Jun 2017 09:57:27 -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> From: Andrey Ryabinin Message-ID: <75ea368f-9268-44fd-f3f6-2a48dc8d2fe8@virtuozzo.com> Date: Thu, 1 Jun 2017 19:59:20 +0300 MIME-Version: 1.0 In-Reply-To: <20170601165205.GA8191@leverpostej> 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 07:52 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 > 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