On 27.11.2018 21:11, Jonathan Corbet wrote: > 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. Thanks for meaningful comments! Looking forward to ack from perf world. > > 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. Thanks, Alexey > > jon >
