From patchwork Wed Jun 15 17:04:45 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Rutland X-Patchwork-Id: 70121 Delivered-To: patch@linaro.org Received: by 10.140.106.246 with SMTP id e109csp2676547qgf; Wed, 15 Jun 2016 10:05:16 -0700 (PDT) X-Received: by 10.107.52.133 with SMTP id b127mr872893ioa.6.1466010316633; Wed, 15 Jun 2016 10:05:16 -0700 (PDT) Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id fa5si1972544pab.13.2016.06.15.10.05.16; Wed, 15 Jun 2016 10:05:16 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932934AbcFORFN (ORCPT + 30 others); Wed, 15 Jun 2016 13:05:13 -0400 Received: from foss.arm.com ([217.140.101.70]:39017 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932659AbcFORFK (ORCPT ); Wed, 15 Jun 2016 13:05:10 -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 0905D2A2; Wed, 15 Jun 2016 10:05:50 -0700 (PDT) Received: from leverpostej.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 7CAE53F246; Wed, 15 Jun 2016 10:05:07 -0700 (PDT) From: Mark Rutland To: linux-kernel@vger.kernel.org Cc: Mark Rutland , Alexander Potapenko , Andrew Morton , Dmitry Vyukov , James Morse , Kees Cook , Michal Marek Subject: [PATCHv2] kcov: reject open when kernel not instrumented Date: Wed, 15 Jun 2016 18:04:45 +0100 Message-Id: <1466010285-2772-1-git-send-email-mark.rutland@arm.com> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If the toolchain does not support -fsanitize-coverage=trace-pc, we blat this option from CFLAGS_KCOV, and build the kernel without instrumentation, even if CONFIG_KCOV was selected. However, we still build the rest of the kcov infrastructure, and expose a kcov file under debugfs. This can be confusing, as the kernel will appear to support kcov, yet will never manage to sample any trace PC values. While we do note this fact at build time, this may be missed, and a user may not have access to build logs. This patch ensures that CC_HAVE_SANCOV_TRACE_PC is defined when the toolchain supports -fsanitize-coverage=trace-pc, and is not defined otherwise. When CC_HAVE_SANCOV_TRACE_PC is not defined, the kernel will return -ENOTSUPP if userspace attempts to open the kcov debugfs file, indicating that kcov functionality is unavailable. Signed-off-by: Mark Rutland Cc: Alexander Potapenko Cc: Andrew Morton Cc: Dmitry Vyukov Cc: James Morse Cc: Kees Cook Cc: Michal Marek Cc: linux-kernel@vger.kernel.org --- Makefile | 2 +- kernel/kcov.c | 9 +++++++++ 2 files changed, 10 insertions(+), 1 deletion(-) Since v1 [1]: * Use CC_HAVE_SANCOV_TRACE_PC rather than CONFIG_KCOV_CC [1] lkml.kernel.org/r/1466005756-15626-1-git-send-email-mark.rutland@arm.com -- 1.9.1 diff --git a/Makefile b/Makefile index 0f70de6..3785a63 100644 --- a/Makefile +++ b/Makefile @@ -369,7 +369,7 @@ LDFLAGS_MODULE = CFLAGS_KERNEL = AFLAGS_KERNEL = CFLAGS_GCOV = -fprofile-arcs -ftest-coverage -fno-tree-loop-im -Wno-maybe-uninitialized -CFLAGS_KCOV = -fsanitize-coverage=trace-pc +CFLAGS_KCOV = -fsanitize-coverage=trace-pc -DCC_HAVE_SANCOV_TRACE_PC # Use USERINCLUDE when you must reference the UAPI directories only. diff --git a/kernel/kcov.c b/kernel/kcov.c index a02f2dd..0a0b164 100644 --- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -3,6 +3,7 @@ #define DISABLE_BRANCH_PROFILING #include #include +#include #include #include #include @@ -160,6 +161,14 @@ static int kcov_open(struct inode *inode, struct file *filep) { struct kcov *kcov; +#ifndef CC_HAVE_SANCOV_TRACE_PC + /* + * CONFIG_KCOV was selected, but the compiler does not support the + * options KCOV requires. + */ + return -ENOTSUPP; +#endif /* CC_HAVE_SANCOV_TRACE_PC */ + kcov = kzalloc(sizeof(*kcov), GFP_KERNEL); if (!kcov) return -ENOMEM;