Date: Tue, 27 Nov 2018 11:11:48 -0700 From: Jonathan Corbet <corbet@....net> To: Alexey Budankov <alexey.budankov@...ux.intel.com> Cc: Thomas Gleixner <tglx@...utronix.de>, Kees Cook <keescook@...omium.org>, Jann Horn <jannh@...gle.com>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Andi Kleen <ak@...ux.intel.com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, Tvrtko Ursulin <tursulin@...ulin.net>, linux-kernel <linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org> Subject: Re: [PATCH v4 1/2] Documentation/admin-guide: introduce perf-security.rst file On Tue, 27 Nov 2018 11:15:37 +0300 Alexey Budankov <alexey.budankov@...ux.intel.com> wrote: > +To perform security checks, the Linux implementation splits processes into two > +categories _ : 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 _ (usually: effective UID, effective GID, and > +supplementary group list). > + > +Linux divides the privileges traditionally associated with superuser into > +distinct units, known as capabilities _ , 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 _ , 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
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