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Date: Tue, 14 Jul 2020 12:27:38 -0300 From: Arnaldo Carvalho de Melo <acme@...nel.org> To: Peter Zijlstra <peterz@...radead.org> Cc: Alexey Budankov <alexey.budankov@...ux.intel.com>, Ravi Bangoria <ravi.bangoria@...ux.ibm.com>, Alexei Starovoitov <ast@...nel.org>, Ingo Molnar <mingo@...hat.com>, James Morris <jmorris@...ei.org>, Namhyung Kim <namhyung@...nel.org>, Serge Hallyn <serge@...lyn.com>, Jiri Olsa <jolsa@...hat.com>, Song Liu <songliubraving@...com>, Andi Kleen <ak@...ux.intel.com>, Stephane Eranian <eranian@...gle.com>, Igor Lubashev <ilubashe@...mai.com>, Thomas Gleixner <tglx@...utronix.de>, linux-kernel <linux-kernel@...r.kernel.org>, "linux-security-module@...r.kernel.org" <linux-security-module@...r.kernel.org>, "selinux@...r.kernel.org" <selinux@...r.kernel.org>, "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, linux-man@...r.kernel.org Subject: Re: [PATCH v8 00/12] Introduce CAP_PERFMON to secure system performance monitoring and observability Em Tue, Jul 14, 2020 at 12:59:34PM +0200, Peter Zijlstra escreveu: > On Mon, Jul 13, 2020 at 03:51:52PM -0300, Arnaldo Carvalho de Melo wrote: > > > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > > > index 856d98c36f56..a2397f724c10 100644 > > > > --- a/kernel/events/core.c > > > > +++ b/kernel/events/core.c > > > > @@ -11595,7 +11595,7 @@ SYSCALL_DEFINE5(perf_event_open, > > > > * perf_event_exit_task() that could imply). > > > > */ > > > > err = -EACCES; > > > > - if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) > > > > + if (!perfmon_capable() && !ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) > > > > goto err_cred; > > > > } > > > >> makes monitoring simpler and even more secure to use since Perf tool need > > > >> not to start/stop/single-step and read/write registers and memory and so on > > > >> like a debugger or strace-like tool. What do you think? > > > > I tend to agree, Peter? > So this basically says that if CAP_PERFMON, we don't care about the > ptrace() permissions? Just like how CAP_SYS_PTRACE would always allow > the ptrace checks? > I suppose that makes sense. Yeah, it in fact addresses the comment right above it: if (task) { err = mutex_lock_interruptible(&task->signal->exec_update_mutex); if (err) goto err_task; /* * Reuse ptrace permission checks for now. * * We must hold exec_update_mutex across this and any potential * perf_install_in_context() call for this new event to * serialize against exec() altering our credentials (and the * perf_event_exit_task() that could imply). */ err = -EACCES; if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) goto err_cred; } that "for now" part :-) Idea is to not require CAP_PTRACE for that, i.e. the attack surface for the perf binary is reduced. - Arnaldo
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