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Fri, 16 Oct 2020 08:30:55 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 5CE2FC433FF; Fri, 16 Oct 2020 08:30:54 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: saiprakash.ranjan) by smtp.codeaurora.org (Postfix) with ESMTPSA id 770DCC433CB; Fri, 16 Oct 2020 08:30:53 +0000 (UTC) MIME-Version: 1.0 Date: Fri, 16 Oct 2020 14:00:53 +0530 From: Sai Prakash Ranjan To: Suzuki K Poulose Subject: Re: [PATCH] coresight: etm4x: Add config to exclude kernel mode tracing In-Reply-To: References: <20201015124522.1876-1-saiprakash.ranjan@codeaurora.org> Message-ID: <2b5c14ca55b57430ac1d7aac533d45de@codeaurora.org> X-Sender: saiprakash.ranjan@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201016_043118_492284_A83DC941 X-CRM114-Status: GOOD ( 32.71 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: denik@chromium.org, mathieu.poirier@linaro.org, peterz@infradead.org, linux-arm-msm@vger.kernel.org, coresight@lists.linaro.org, linux-kernel@vger.kernel.org, swboyd@chromium.org, linux-arm-kernel@lists.infradead.org, mike.leach@linaro.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Suzuki, On 2020-10-15 19:57, Suzuki K Poulose wrote: > Hi Sai, > > On 10/15/2020 01:45 PM, Sai Prakash Ranjan wrote: >> On production systems with ETMs enabled, it is preferred to >> exclude kernel mode(NS EL1) tracing for security concerns and >> support only userspace(NS EL0) tracing. So provide an option >> via kconfig to exclude kernel mode tracing if it is required. >> This config is disabled by default and would not affect the >> current configuration which has both kernel and userspace >> tracing enabled by default. > > While this solution works for ETM4x, I would prefer if we did > this in a more generic way. There are other hardware tracing > PMUs that provide instruction tracing (e.g, Intel PT, even ETM3x) > and it would be good to have a single option that works everywhere. > > Something like EXCLUDE_KERNEL_HW_ITRACE, which can be honored by > all tracing drivers ? I can add this for ETM3x as well but I have zero idea regarding Intel PTs, is there any code in those hwtracing PMUs actually excluding kernel mode tracing currently? >> >> Signed-off-by: Sai Prakash Ranjan >> --- >> drivers/hwtracing/coresight/Kconfig | 9 +++++++++ >> drivers/hwtracing/coresight/coresight-etm4x-core.c | 6 +++++- >> 2 files changed, 14 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/hwtracing/coresight/Kconfig >> b/drivers/hwtracing/coresight/Kconfig >> index c1198245461d..52435de8824c 100644 >> --- a/drivers/hwtracing/coresight/Kconfig >> +++ b/drivers/hwtracing/coresight/Kconfig >> @@ -110,6 +110,15 @@ config CORESIGHT_SOURCE_ETM4X >> To compile this driver as a module, choose M here: the >> module will be called coresight-etm4x. >> +config CORESIGHT_ETM4X_EXCL_KERN >> + bool "Coresight ETM 4.x exclude kernel mode tracing" >> + depends on CORESIGHT_SOURCE_ETM4X >> + help >> + This will exclude kernel mode(NS EL1) tracing if enabled. This >> option >> + will be useful to provide more flexible options on production >> systems >> + where only userspace(NS EL0) tracing might be preferred for >> security >> + reasons. >> + >> config CORESIGHT_STM >> tristate "CoreSight System Trace Macrocell driver" >> depends on (ARM && !(CPU_32v3 || CPU_32v4 || CPU_32v4T)) || ARM64 >> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c >> b/drivers/hwtracing/coresight/coresight-etm4x-core.c >> index abd706b216ac..7e5669e5cd1f 100644 >> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c >> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c >> @@ -832,6 +832,9 @@ static u64 etm4_get_ns_access_type(struct >> etmv4_config *config) >> { >> u64 access_type = 0; >> + if (IS_ENABLED(CONFIG_CORESIGHT_ETM4X_EXCL_KERN)) >> + config->mode |= ETM_MODE_EXCL_KERN; >> + > > Rather than hacking the mode behind the back, could we always make sure > that > mode is not set in the first place and return this back to the user > with > proper errors (see below) ? > Sure, this was the minimal change with which I could keep the check in one place which would work for both sysfs and perf, but I'll change as you suggested and move the check to etm4_parse_event_config() and etm4_config_trace_mode() and return errors properly. >> /* >> * EXLEVEL_NS, bits[15:12] >> * The Exception levels are: >> @@ -849,7 +852,8 @@ static u64 etm4_get_ns_access_type(struct >> etmv4_config *config) >> access_type = ETM_EXLEVEL_NS_HYP; >> } >> - if (config->mode & ETM_MODE_EXCL_USER) >> + if (config->mode & ETM_MODE_EXCL_USER && >> + !IS_ENABLED(CONFIG_CORESIGHT_ETM4X_EXCL_KERN)) >> access_type |= ETM_EXLEVEL_NS_APP; > > Why is this needed ? > Yes this will not be required as excluding both doesn't make sense and we print warning in that case already, will drop this. > Also we should return an error if the sysfs mode ever tries to clear > the mode bit > for kernel in config->mode. > Yes will change as explained in above comment. Thanks, Sai -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel