On 08.01.2020 19:07, Peter Zijlstra wrote:

On Wed, Dec 18, 2019 at 12:25:35PM +0300, Alexey Budankov wrote:

quoted

Open access to perf_events monitoring for CAP_SYS_PERFMON privileged
processes. For backward compatibility reasons access to perf_events
subsystem remains open for CAP_SYS_ADMIN privileged processes but
CAP_SYS_ADMIN usage for secure perf_events monitoring is discouraged
with respect to CAP_SYS_PERFMON capability.

Signed-off-by: Alexey Budankov <redacted>
---
 include/linux/perf_event.h | 6 +++---
 kernel/events/core.c       | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 34c7c6910026..f46acd69425f 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h

@@ -1285,7 +1285,7 @@ static inline int perf_is_paranoid(void)
 
 static inline int perf_allow_kernel(struct perf_event_attr *attr)
 {
-	if (sysctl_perf_event_paranoid > 1 && !capable(CAP_SYS_ADMIN))
+	if (sysctl_perf_event_paranoid > 1 && !perfmon_capable())
 		return -EACCES;
 
 	return security_perf_event_open(attr, PERF_SECURITY_KERNEL);

@@ -1293,7 +1293,7 @@ static inline int perf_allow_kernel(struct perf_event_attr *attr)
 
 static inline int perf_allow_cpu(struct perf_event_attr *attr)
 {
-	if (sysctl_perf_event_paranoid > 0 && !capable(CAP_SYS_ADMIN))
+	if (sysctl_perf_event_paranoid > 0 && !perfmon_capable())
 		return -EACCES;
 
 	return security_perf_event_open(attr, PERF_SECURITY_CPU);

@@ -1301,7 +1301,7 @@ static inline int perf_allow_cpu(struct perf_event_attr *attr)
 
 static inline int perf_allow_tracepoint(struct perf_event_attr *attr)
 {
-	if (sysctl_perf_event_paranoid > -1 && !capable(CAP_SYS_ADMIN))
+	if (sysctl_perf_event_paranoid > -1 && !perfmon_capable())
 		return -EPERM;
 
 	return security_perf_event_open(attr, PERF_SECURITY_TRACEPOINT);

These are OK I suppose.

quoted

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 059ee7116008..d9db414f2197 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c

@@ -9056,7 +9056,7 @@ static int perf_kprobe_event_init(struct perf_event *event)
 	if (event->attr.type != perf_kprobe.type)
 		return -ENOENT;
 
-	if (!capable(CAP_SYS_ADMIN))
+	if (!perfmon_capable())
 		return -EACCES;
 
 	/*

This one only allows attaching to already extant kprobes, right? It does
not allow creation of kprobes.

This unblocks creation of local trace kprobes and uprobes by CAP_SYS_PERFMON 
privileged process, exactly the same as for CAP_SYS_ADMIN privileged process.

quoted

@@ -9116,7 +9116,7 @@ static int perf_uprobe_event_init(struct perf_event *event)
 	if (event->attr.type != perf_uprobe.type)
 		return -ENOENT;
 
-	if (!capable(CAP_SYS_ADMIN))
+	if (!perfmon_capable())
 		return -EACCES;
 
 	/*

Idem, I presume.

quoted

@@ -11157,7 +11157,7 @@ SYSCALL_DEFINE5(perf_event_open,
 	}
 
 	if (attr.namespaces) {
-		if (!capable(CAP_SYS_ADMIN))
+		if (!perfmon_capable())
 			return -EACCES;
 	}

And given we basically make the entire kernel observable with this CAP,
busting namespaces shoulnd't be a problem either.

So yeah, I suppose that works.