On Tue, 27 Nov 2018 11:15:37 +0300 Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx> wrote: > +To perform security checks, the Linux implementation splits processes into two > +categories [6]_ : a) privileged processes (whose effective user ID is 0, referred > +to as superuser or root), and b) unprivileged processes (whose effective UID is > +nonzero). Privileged processes bypass all kernel security permission checks so > +perf_events performance monitoring is fully available to privileged processes > +without access, scope and resource restrictions. > + > +Unprivileged processes are subject to a full security permission check based on > +the process's credentials [5]_ (usually: effective UID, effective GID, and > +supplementary group list). > + > +Linux divides the privileges traditionally associated with superuser into > +distinct units, known as capabilities [6]_ , which can be independently enabled > +and disabled on per-thread basis for processes and files of unprivileged users. > + > +Unprivileged processes with enabled CAP_SYS_ADMIN capability are treated as > +privileged processes with respect to perf_events performance monitoring and > +bypass *scope* permissions checks in the kernel. > + > +Unprivileged processes using perf_events system call API is also subject for > +PTRACE_MODE_READ_REALCREDS ptrace access mode check [7]_ , whose outcome > +determines whether monitoring is permitted. So unprivileged processes provided > +with CAP_SYS_PTRACE capability are effectively permitted to pass the check. It's good to have more information here. I could certainly quibble further with things - a process with CAP_SYS_ADMIN is not "unprivileged"! - but I don't want to stand in the way of this any further. I *would* still like to see an ack from the perf world, though. With regard to Kees's comment on merging the two patches; I would probably add the new document to index.rst in the same patch, but it doesn't matter that much. Not worth redoing the patch just for that. jon
