Re: [PATCH 3/4] coresight: etm4x: Add support to exclude kernel mode tracing
Hi, Thanks for taking a look, comments inline. On 2021-02-23 01:44, Doug Anderson wrote: Hi, On Fri, Jan 29, 2021 at 11:08 AM Sai Prakash Ranjan wrote: @@ -1202,6 +1207,13 @@ void etm4_config_trace_mode(struct etmv4_config *config) /* excluding kernel AND user space doesn't make sense */ WARN_ON_ONCE(mode == (ETM_MODE_EXCL_KERN | ETM_MODE_EXCL_USER)); + if (!(mode & ETM_MODE_EXCL_KERN) && IS_ENABLED(CONFIG_EXCLUDE_KERNEL_HW_ITRACE)) { + dev_err(>csdev->dev, + "Kernel mode tracing is not allowed, check your kernel config\n"); + config->mode |= ETM_MODE_EXCL_KERN; + return; So I'm not an expert on this code, but the above looks suspicious to me. Specifically you are still modifying "config->mode" even though printing an "error" (dev_err, not dev_warn) and then skipping the rest of this function. Since you're skipping the rest of this function you're not applying the access, right? Naively I'd have expected one of these: 1. Maybe the "dev_err" should be a "dev_warn" and then you shouldn't "return". In this case you're just implicitly adding "ETM_MODE_EXCL_KERN" (and shouting) but then making things work. Of course, then what happens if the user already specified "ETM_MODE_EXCL_USER" too? As per the comment above that "doesn't make sense". ...so maybe the code wouldn't behave properly... 2. Maybe you should be modifying this function to return an error code. mode_store() which is the caller of this function sets the config->mode based on the value passed in the sysfs, so if the user passes the mode which doesn't exclude the kernel even though the kernel config is enabled and the code just sets it, then that is an error and the user should be warned about, so I used dev_err, but I can change it to dev_warn if that is preferred. And to make sysfs mode show the original mode after failure, I set the mode in etm4_config_trace_mode(). But you are right, I am skipping to set the config for other mode bits and returning which is wrong, will fix it as you suggest below. 3. Maybe you should just be updating the one caller of this function to error check this right at the beginning of the function and then fail the sysfs write if the user did the wrong thing. Then in etm4_config_trace_mode you could just have a WARN_ON_ONCE if the kernel wasn't excluded... Right, will do this. Thanks, Sai -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation
Re: [PATCH 3/4] coresight: etm4x: Add support to exclude kernel mode tracing
Hi, On Fri, Jan 29, 2021 at 11:08 AM Sai Prakash Ranjan wrote: > > @@ -1202,6 +1207,13 @@ void etm4_config_trace_mode(struct etmv4_config > *config) > /* excluding kernel AND user space doesn't make sense */ > WARN_ON_ONCE(mode == (ETM_MODE_EXCL_KERN | ETM_MODE_EXCL_USER)); > > + if (!(mode & ETM_MODE_EXCL_KERN) && > IS_ENABLED(CONFIG_EXCLUDE_KERNEL_HW_ITRACE)) { > + dev_err(>csdev->dev, > + "Kernel mode tracing is not allowed, check your > kernel config\n"); > + config->mode |= ETM_MODE_EXCL_KERN; > + return; So I'm not an expert on this code, but the above looks suspicious to me. Specifically you are still modifying "config->mode" even though printing an "error" (dev_err, not dev_warn) and then skipping the rest of this function. Since you're skipping the rest of this function you're not applying the access, right? Naively I'd have expected one of these: 1. Maybe the "dev_err" should be a "dev_warn" and then you shouldn't "return". In this case you're just implicitly adding "ETM_MODE_EXCL_KERN" (and shouting) but then making things work. Of course, then what happens if the user already specified "ETM_MODE_EXCL_USER" too? As per the comment above that "doesn't make sense". ...so maybe the code wouldn't behave properly... 2. Maybe you should be modifying this function to return an error code. 3. Maybe you should just be updating the one caller of this function to error check this right at the beginning of the function and then fail the sysfs write if the user did the wrong thing. Then in etm4_config_trace_mode you could just have a WARN_ON_ONCE if the kernel wasn't excluded... -Doug
[PATCH 3/4] coresight: etm4x: Add support to exclude kernel mode tracing
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. Perf subsystem interface for ETMs use the newly introduced kernel config CONFIG_EXCLUDE_KERNEL_HW_ITRACE to exclude kernel mode tracing, but there is an additional interface via sysfs for ETMs which also needs to be handled to exclude kernel mode tracing. So we use this same generic kernel config to handle the sysfs mode of tracing. This config is disabled by default and would not affect the current configuration which has both kernel and userspace tracing enabled by default. Tested-by: Denis Nikitin Signed-off-by: Sai Prakash Ranjan --- drivers/hwtracing/coresight/coresight-etm4x-core.c | 14 +- .../hwtracing/coresight/coresight-etm4x-sysfs.c| 3 ++- 2 files changed, 15 insertions(+), 2 deletions(-) diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c index b20b6ff17cf6..f94143057bb8 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c @@ -1052,12 +1052,16 @@ static void etm4_set_default(struct etmv4_config *config) return; /* -* Make default initialisation trace everything +* Make default initialisation trace everything when +* CONFIG_EXCLUDE_KERNEL_HW_ITRACE is disabled. * * This is done by a minimum default config sufficient to enable * full instruction trace - with a default filter for trace all * achieved by having no filtering. */ + if (IS_ENABLED(CONFIG_EXCLUDE_KERNEL_HW_ITRACE)) + config->mode |= ETM_MODE_EXCL_KERN; + etm4_set_default_config(config); etm4_set_default_filter(config); } @@ -1195,6 +1199,7 @@ static int etm4_set_event_filters(struct etmv4_drvdata *drvdata, void etm4_config_trace_mode(struct etmv4_config *config) { u32 mode; + struct etmv4_drvdata *drvdata = container_of(config, struct etmv4_drvdata, config); mode = config->mode; mode &= (ETM_MODE_EXCL_KERN | ETM_MODE_EXCL_USER); @@ -1202,6 +1207,13 @@ void etm4_config_trace_mode(struct etmv4_config *config) /* excluding kernel AND user space doesn't make sense */ WARN_ON_ONCE(mode == (ETM_MODE_EXCL_KERN | ETM_MODE_EXCL_USER)); + if (!(mode & ETM_MODE_EXCL_KERN) && IS_ENABLED(CONFIG_EXCLUDE_KERNEL_HW_ITRACE)) { + dev_err(>csdev->dev, + "Kernel mode tracing is not allowed, check your kernel config\n"); + config->mode |= ETM_MODE_EXCL_KERN; + return; + } + /* nothing to do if neither flags are set */ if (!(mode & ETM_MODE_EXCL_KERN) && !(mode & ETM_MODE_EXCL_USER)) return; diff --git a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c index 989ce7b8ade7..f1d19d69d151 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c +++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c @@ -426,7 +426,8 @@ static ssize_t mode_store(struct device *dev, else config->vinst_ctrl &= ~BIT(11); - if (config->mode & (ETM_MODE_EXCL_KERN | ETM_MODE_EXCL_USER)) + if ((config->mode & (ETM_MODE_EXCL_KERN | ETM_MODE_EXCL_USER)) || + IS_ENABLED(CONFIG_EXCLUDE_KERNEL_HW_ITRACE)) etm4_config_trace_mode(config); spin_unlock(>spinlock); -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation