Re: [PATCH 1/2] coresight: tmc: Don't change the buffer size if it's in use
From: James Clark <james.clark@linaro.org>
Date: 2024-11-14 11:25:30
On 14/11/2024 8:16 am, Yicong Yang wrote:
quoted hunk ↗ jump to hunk
From: Yicong Yang <yangyicong@hisilicon.com> Enable the trace in below steps will crash the kernel by NULL pointer dereferencing: echo 1 > /sys/bus/coresight/devices/tmc_etr0/enable_sink echo 1 > /sys/bus/coresight/devices/etm0/enable_source echo 0x400000 > /sys/bus/coresight/devices/tmc_etr0/buffer_size echo 1 > /sys/bus/coresight/devices/etm2/enable_source dd if=/dev/tmc_etr0 of=test_etm_sysfs_etr_030.data The call trace will be like: WARNING: CPU: 39 PID: 8586 at drivers/hwtracing/coresight/coresight-tmc-etr.c:1123 __tmc_etr_disable_hw+0x108/0x140 [coresight_tmc] [...] Call trace: __tmc_etr_disable_hw+0x108/0x140 [coresight_tmc] tmc_read_prepare_etr+0xc0/0xd0 [coresight_tmc] tmc_open+0x60/0xa0 [coresight_tmc] misc_open+0x11c/0x170 chrdev_open+0xcc/0x2b0 do_dentry_open+0x140/0x4e0 vfs_open+0x34/0xf8 path_openat+0x2b0/0xf58 do_filp_open+0x8c/0x148 do_sys_openat2+0xb8/0xe8 __arm64_sys_openat+0x70/0xc0 el0_svc_common.constprop.0+0x64/0x148 do_el0_svc+0x24/0x38 el0_svc+0x40/0x140 el0t_64_sync_handler+0xc0/0xc8 el0t_64_sync+0x1a4/0x1a8 ---[ end trace 0000000000000000 ]--- Unable to handle kernel NULL pointer dereference at virtual address 0000000000000028 [...] Call trace: tmc_etr_get_sysfs_trace+0x10/0x80 [coresight_tmc] vfs_read+0xcc/0x310 ksys_read+0x74/0x108 __arm64_sys_read+0x24/0x38 el0_svc_common.constprop.0+0x64/0x148 do_el0_svc+0x24/0x38 el0_svc+0x40/0x140 Due to the buffer size changed, the buffer will be reallocated in tmc_etr_get_sysfs_buffer() when the second source enabled. At trace end tmc_etr_sync_sysfs_buf() will reset the drvdata->sysfs_buf and trigger the later NULL pointer dereference when reading out the data. But it doesn't make sense to change the buffer size when it's already in use. So block such behavior. Signed-off-by: Yicong Yang <yangyicong@hisilicon.com> --- drivers/hwtracing/coresight/coresight-tmc-core.c | 5 +++++ 1 file changed, 5 insertions(+)diff --git a/drivers/hwtracing/coresight/coresight-tmc-core.c b/drivers/hwtracing/coresight/coresight-tmc-core.c index 475fa4bb6813..9660af63e9bc 100644 --- a/drivers/hwtracing/coresight/coresight-tmc-core.c +++ b/drivers/hwtracing/coresight/coresight-tmc-core.c@@ -319,6 +319,11 @@ static ssize_t buffer_size_store(struct device *dev, if (drvdata->config_type != TMC_CONFIG_TYPE_ETR) return -EPERM; + /* Don't change the buffer size if it's in use */ + guard(spinlock)(&drvdata->spinlock); + if (coresight_get_mode(drvdata->csdev) != CS_MODE_DISABLED)
Size isn't used in perf mode is it? So it can be -EBUSY only when mode == CS_MODE_SYSFS.
+ return -EBUSY; + ret = kstrtoul(buf, 0, &val); if (ret) return ret;
Looks ok to me. Although for consistency it might be worth changing to
guard(mutex)(&coresight_mutex) because this is about sysfs mode only and
other usages of mode and comments point to coresight_mutex. Using the
device's spinlock will technically work but it did make me go and double
check the code. And there are other cases of reading the mode like this:
static ssize_t enable_source_show(struct device *dev,
struct device_attribute *attr,
char *buf)
{
struct coresight_device *csdev = to_coresight_device(dev);
guard(mutex)(&coresight_mutex);
return scnprintf(buf, PAGE_SIZE, "%u\n",
coresight_get_mode(csdev) == CS_MODE_SYSFS);
}
Mode can change to CS_MODE_PERF while inside coresight_mutex but the
device would end up not being enabled for sysfs, so it's still ok to
update the sysfs size value in that case.
With that change:
Reviewed-by: James Clark <james.clark@linaro.org>