From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 93542C28CC0 for ; Wed, 29 May 2019 13:26:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 65DBC2183F for ; Wed, 29 May 2019 13:26:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727236AbfE2N0G (ORCPT ); Wed, 29 May 2019 09:26:06 -0400 Received: from foss.arm.com ([217.140.101.70]:46006 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726029AbfE2N0G (ORCPT ); Wed, 29 May 2019 09:26:06 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8CE4C80D; Wed, 29 May 2019 06:26:05 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8F6763F59C; Wed, 29 May 2019 06:26:02 -0700 (PDT) Date: Wed, 29 May 2019 14:26:00 +0100 From: Mark Rutland To: Dmitry Vyukov Cc: Peter Zijlstra , Marco Elver , Andrey Ryabinin , Alexander Potapenko , Andrey Konovalov , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , the arch/x86 maintainers , Arnd Bergmann , Josh Poimboeuf , "open list:DOCUMENTATION" , LKML , linux-arch , kasan-dev Subject: Re: [PATCH 3/3] asm-generic, x86: Add bitops instrumentation for KASAN Message-ID: <20190529132559.GF31777@lakrids.cambridge.arm.com> References: <20190528163258.260144-1-elver@google.com> <20190528163258.260144-3-elver@google.com> <20190528165036.GC28492@lakrids.cambridge.arm.com> <20190529100116.GM2623@hirez.programming.kicks-ass.net> <20190529103010.GP2623@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 29, 2019 at 12:57:15PM +0200, Dmitry Vyukov wrote: > On Wed, May 29, 2019 at 12:30 PM Peter Zijlstra wrote: > > > > On Wed, May 29, 2019 at 12:16:31PM +0200, Marco Elver wrote: > > > On Wed, 29 May 2019 at 12:01, Peter Zijlstra wrote: > > > > > > > > On Wed, May 29, 2019 at 11:20:17AM +0200, Marco Elver wrote: > > > > > For the default, we decided to err on the conservative side for now, > > > > > since it seems that e.g. x86 operates only on the byte the bit is on. > > > > > > > > This is not correct, see for instance set_bit(): > > > > > > > > static __always_inline void > > > > set_bit(long nr, volatile unsigned long *addr) > > > > { > > > > if (IS_IMMEDIATE(nr)) { > > > > asm volatile(LOCK_PREFIX "orb %1,%0" > > > > : CONST_MASK_ADDR(nr, addr) > > > > : "iq" ((u8)CONST_MASK(nr)) > > > > : "memory"); > > > > } else { > > > > asm volatile(LOCK_PREFIX __ASM_SIZE(bts) " %1,%0" > > > > : : RLONG_ADDR(addr), "Ir" (nr) : "memory"); > > > > } > > > > } > > > > > > > > That results in: > > > > > > > > LOCK BTSQ nr, (addr) > > > > > > > > when @nr is not an immediate. > > > > > > Thanks for the clarification. Given that arm64 already instruments > > > bitops access to whole words, and x86 may also do so for some bitops, > > > it seems fine to instrument word-sized accesses by default. Is that > > > reasonable? > > > > Eminently -- the API is defined such; for bonus points KASAN should also > > do alignment checks on atomic ops. Future hardware will #AC on unaligned > > [*] LOCK prefix instructions. > > > > (*) not entirely accurate, it will only trap when crossing a line. > > https://lkml.kernel.org/r/1556134382-58814-1-git-send-email-fenghua.yu@intel.com > > Interesting. Does an address passed to bitops also should be aligned, > or alignment is supposed to be handled by bitops themselves? > > This probably should be done as a separate config as not related to > KASAN per se. But obviously via the same > {atomicops,bitops}-instrumented.h hooks which will make it > significantly easier. Makes sense to me -- that should be easy to hack into gen_param_check() in gen-atomic-instrumented.sh, something like: ---- diff --git a/scripts/atomic/gen-atomic-instrumented.sh b/scripts/atomic/gen-atomic-instrumented.sh index e09812372b17..2f6b8f521e57 100755 --- a/scripts/atomic/gen-atomic-instrumented.sh +++ b/scripts/atomic/gen-atomic-instrumented.sh @@ -21,6 +21,13 @@ gen_param_check() [ ${type#c} != ${type} ] && rw="read" printf "\tkasan_check_${rw}(${name}, sizeof(*${name}));\n" + + [ "${type#c}" = "v" ] || return + +cat <