linux-kernel - [RFC 1/4] perf: Move some access checks later in perf_event

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Date:   Tue, 26 Jun 2018 16:36:39 +0100
From:   Tvrtko Ursulin <tursulin@...ulin.net>
To:     linux-kernel@...r.kernel.org
Cc:     Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        x86@...nel.org
Subject: [RFC 1/4] perf: Move some access checks later in perf_event_open

From: Tvrtko Ursulin <tvrtko.ursulin@...el.com>

To enable per-PMU access controls in a following patch first move all call
sites of perf_paranoid_kernel() to after the event has been created.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org
Cc: x86@...nel.org
---
 kernel/events/core.c | 36 ++++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index f490caca9aa4..12de95b0472e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10189,10 +10189,6 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
 			 */
 			attr->branch_sample_type = mask;
 		}
-		/* privileged levels capture (kernel, hv): check permissions */
-		if ((mask & PERF_SAMPLE_BRANCH_PERM_PLM)
-		    && perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
-			return -EACCES;
 	}
 
 	if (attr->sample_type & PERF_SAMPLE_REGS_USER) {
@@ -10409,11 +10405,6 @@ SYSCALL_DEFINE5(perf_event_open,
 	if (err)
 		return err;
 
-	if (!attr.exclude_kernel) {
-		if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
-			return -EACCES;
-	}
-
 	if (attr.namespaces) {
 		if (!capable(CAP_SYS_ADMIN))
 			return -EACCES;
@@ -10427,11 +10418,6 @@ SYSCALL_DEFINE5(perf_event_open,
 			return -EINVAL;
 	}
 
-	/* Only privileged users can get physical addresses */
-	if ((attr.sample_type & PERF_SAMPLE_PHYS_ADDR) &&
-	    perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
-		return -EACCES;
-
 	/*
 	 * In cgroup mode, the pid argument is used to pass the fd
 	 * opened to the cgroup directory in cgroupfs. The cpu argument
@@ -10501,6 +10487,28 @@ SYSCALL_DEFINE5(perf_event_open,
 		goto err_cred;
 	}
 
+	if (!attr.exclude_kernel) {
+		if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN)) {
+			err = -EACCES;
+			goto err_alloc;
+		}
+	}
+
+	/* Only privileged users can get physical addresses */
+	if ((attr.sample_type & PERF_SAMPLE_PHYS_ADDR) &&
+	    perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN)) {
+		err = -EACCES;
+		goto err_alloc;
+	}
+
+	/* privileged levels capture (kernel, hv): check permissions */
+	if ((attr.sample_type & PERF_SAMPLE_BRANCH_STACK) &&
+	    (attr.branch_sample_type & PERF_SAMPLE_BRANCH_PERM_PLM) &&
+	    perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN)) {
+		err = -EACCES;
+		goto err_alloc;
+	}
+
 	if (is_sampling_event(event)) {
 		if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) {
 			err = -EOPNOTSUPP;
-- 
2.17.1