Date: Mon, 3 Dec 2018 12:42:09 +0300 From: Alexey Budankov <alexey.budankov@...ux.intel.com> To: Jonathan Corbet <corbet@....net>, Peter Zijlstra <peterz@...radead.org> Cc: Thomas Gleixner <tglx@...utronix.de>, Kees Cook <keescook@...omium.org>, Jann Horn <jannh@...gle.com>, Ingo Molnar <mingo@...hat.com>, 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 Hi Peter, On 27.11.2018 22:13, Alexey Budankov wrote: > On 27.11.2018 21:11, Jonathan Corbet wrote: >> 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. > > Thanks for meaningful comments! Looking forward to ack from perf world. May I ask you to review v4 of the patches? Your comments on v1 have been addressed in there. Thanks, Alexey > >> >> 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 >> >
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