Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751902AbdILRmX (ORCPT ); Tue, 12 Sep 2017 13:42:23 -0400 Received: from mail-it0-f42.google.com ([209.85.214.42]:38879 "EHLO mail-it0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751815AbdILRmU (ORCPT ); Tue, 12 Sep 2017 13:42:20 -0400 X-Google-Smtp-Source: AOwi7QCebkvawKTNuZ8kuB/uV1D7xqaaJLdhUr4Ka5DfZH4E/2vZ5h5USv52ajMaZZsZ/0BiV3B7EEasvsr7Z1565Gs= MIME-Version: 1.0 In-Reply-To: References: <663c2a30de845dd13cf3cf64c3dfd437295d5ce2.1504109849.git.dvyukov@google.com> <20170830182357.GD32493@leverpostej> From: Dmitry Vyukov Date: Tue, 12 Sep 2017 19:41:58 +0200 Message-ID: Subject: Re: [PATCH 1/3] kcov: support comparison operands collection To: Mark Rutland Cc: Andrew Morton , "linux-mm@kvack.org" , Victor Chibotaru , Alexander Popov , Andrey Ryabinin , Kees Cook , Vegard Nossum , Quentin Casasnovas , syzkaller , LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2257 Lines: 56 On Wed, Aug 30, 2017 at 9:08 PM, Dmitry Vyukov wrote: > On Wed, Aug 30, 2017 at 8:23 PM, Mark Rutland wrote: >> Hi, >> >> On Wed, Aug 30, 2017 at 06:23:29PM +0200, Dmitry Vyukov wrote: >>> From: Victor Chibotaru >>> >>> Enables kcov to collect comparison operands from instrumented code. >>> This is done by using Clang's -fsanitize=trace-cmp instrumentation >>> (currently not available for GCC). >> >> What's needed to build the kernel with Clang these days? >> >> I was under the impression that it still wasn't possible to build arm64 >> with clang due to a number of missing features (e.g. the %a assembler >> output template). >> >>> The comparison operands help a lot in fuzz testing. E.g. they are >>> used in Syzkaller to cover the interiors of conditional statements >>> with way less attempts and thus make previously unreachable code >>> reachable. >>> >>> To allow separate collection of coverage and comparison operands two >>> different work modes are implemented. Mode selection is now done via >>> a KCOV_ENABLE ioctl call with corresponding argument value. >>> >>> Signed-off-by: Victor Chibotaru >>> Cc: Andrew Morton >>> Cc: Mark Rutland >>> Cc: Alexander Popov >>> Cc: Andrey Ryabinin >>> Cc: Kees Cook >>> Cc: Vegard Nossum >>> Cc: Quentin Casasnovas >>> Cc: syzkaller@googlegroups.com >>> Cc: linux-mm@kvack.org >>> Cc: linux-kernel@vger.kernel.org >>> --- >>> Clang instrumentation: >>> https://clang.llvm.org/docs/SanitizerCoverage.html#tracing-data-flow >> >> How stable is this? >> >> The comment at the end says "This interface is a subject to change." > > > The intention is that this is not subject to change anymore (since we > are using it in kernel). > I've mailed change to docs: https://reviews.llvm.org/D37303 > > FWIW, there is patch in flight that adds this instrumentation to gcc: > https://groups.google.com/forum/#!topic/syzkaller/CSLynn6nI-A > It seems to be stalled on review phase, though. Good news is that this is submitted to gcc in 251801.