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perf: Satisfy the kernel's request to request PMU counters

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The SELinux policy on Android doesn't provide the kernel-space
with CAP_SYS_ADMIN capability. The perf-core checks for this
capability before giving access to the callers to read the PMU
counters. Hence, when the kernel drivers try to gain access
to the PMU (via perf_event_create_kernel_counter()), it fails
with -EACCES.

To get past this, add another condition to check if the request
is coming from kernel-space or user-space. If kernel-space,
don't check for the capability any further and move on.

Change-Id: Ie2ddc6b619fa0d60d4752994ea0c9cedf5b96b5c
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>
This commit is contained in:
Raghavendra Rao Ananta 2020-03-18 11:11:34 -07:00
commit e5ac623a25
2 changed files with 18 additions and 11 deletions
Download patch file Download diff file Expand all files Collapse all files

20
include/linux/perf_event.h
View file

@ -1253,6 +1253,13 @@ int perf_event_max_stack_handler(struct ctl_table *table, int write,
#define PERF_SECURITY_KERNEL 2
#define PERF_SECURITY_TRACEPOINT 3
#define TASK_TOMBSTONE ((void *)-1L)
static bool is_kernel_event(struct perf_event *event)
{
return READ_ONCE(event->owner) == TASK_TOMBSTONE;
}
static inline bool perf_paranoid_any(void)
{
return sysctl_perf_event_paranoid > 2;
@ -1271,12 +1278,19 @@ static inline int perf_allow_kernel(struct perf_event_attr *attr)
return security_perf_event_open(attr, PERF_SECURITY_KERNEL);
}
static inline int perf_allow_cpu(struct perf_event_attr *attr)
static inline int perf_allow_cpu(struct perf_event *event)
{
if (sysctl_perf_event_paranoid > 0 && !capable(CAP_SYS_ADMIN))
if (sysctl_perf_event_paranoid > 0 && !is_kernel_event(event) &&
!capable(CAP_SYS_ADMIN)) {
return -EACCES;
}
return security_perf_event_open(attr, PERF_SECURITY_CPU);
/*
* Bypass the system call security check if the
* event creation is from the kernel
*/
return is_kernel_event(event) ? 0 :
security_perf_event_open(&event->attr, PERF_SECURITY_CPU);
}
static inline int perf_allow_tracepoint(struct perf_event_attr *attr)

9
kernel/events/core.c
View file

@ -164,13 +164,6 @@ static void perf_ctx_unlock(struct perf_cpu_context *cpuctx,
raw_spin_unlock(&cpuctx->ctx.lock);
}
#define TASK_TOMBSTONE ((void *)-1L)
static bool is_kernel_event(struct perf_event *event)
{
return READ_ONCE(event->owner) == TASK_TOMBSTONE;
}
/*
* On task ctx scheduling...
*
@ -4234,7 +4227,7 @@ find_get_context(struct pmu *pmu, struct task_struct *task,
if (!task) {
/* Must be root to operate on a CPU event: */
err = perf_allow_cpu(&event->attr);
err = perf_allow_cpu(event);
if (err)
return ERR_PTR(err);