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Extend error messages to mention CAP_PERFMON capability as an option to
substitute CAP_SYS_ADMIN capability for secure system performance
monitoring and observability operations. Make
perf_event_paranoid_check() and __cmd_ftrace() to be aware of
CAP_PERFMON capability.

CAP_PERFMON implements the principle of least privilege for performance
monitoring and observability operations (POSIX IEEE 1003.1e 2.2.2.39
principle of least privilege: A security design principle that states
that a process or program be granted only those privileges (e.g.,
capabilities) necessary to accomplish its legitimate function, and only
for the time that such privileges are actually required)

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_PERFMON
capability.

Committer testing:

Using a libcap with this patch:

  diff --git ...