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Date: Wed, 18 Feb 2009 21:26:53 +1100
From: Paul Mackerras <paulus@...ba.org>
To: Ingo Molnar <mingo@...e.hu>
CC: linux-kernel@...r.kernel.org
Subject: [PATCH] perfcounters: allow sysadmin to restrict non-root counting of kernel events
Impact: security feature
This allows the sysadmin to prevent non-root users from counting
hardware events that occur in kernel or hypervisor mode via a sysfs file:
/sys/devices/system/cpu/perf_counters/restrict_kernel_events
This defaults to off (0), allowing users to count kernel and hypervisor
events, but if the sysadmin writes 1 to that file, any new counters
created by non-root users will automatically be set to ignore kernel
and hypervisor events.
This could be useful if there is a concern that allowing non-root users
to count kernel or hypervisor events might leak sensitive information.
Signed-off-by: Paul Mackerras <paulus@...ba.org>
---
This is available in my perfcounters.git tree master branch at:
git://git.kernel.org/pub/scm/linux/kernel/git/paulus/perfcounters.git master
kernel/perf_counter.c | 46 +++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 45 insertions(+), 1 deletions(-)
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index ad62965..7967272 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -31,6 +31,7 @@ DEFINE_PER_CPU(struct perf_cpu_context, perf_cpu_context);
int perf_max_counters __read_mostly = 1;
static int perf_reserved_percpu __read_mostly;
static int perf_overcommit __read_mostly = 1;
+static int perf_counters_strict __read_mostly;
/*
* Mutex for (sysadmin-configurable) counter reservations:
@@ -1670,8 +1671,21 @@ perf_counter_alloc(struct perf_counter_hw_event *hw_event,
hw_ops = NULL;
if (!hw_event->raw && hw_event->type < 0)
hw_ops = sw_perf_counter_init(counter);
- else
+ else {
+ /*
+ * If the user is not root and the restrict_kernel_events
+ * policy is in force, make sure we exclude kernel and
+ * hypervisor events from hardware events. (We don't have
+ * any capability to distinguish user, kernel and hypervisor
+ * events in our software counters.)
+ */
+ if (!capable(CAP_SYS_ADMIN) && perf_counters_strict) {
+ counter->hw_event.exclude_kernel = 1;
+ counter->hw_event.exclude_hv = 1;
+ }
+
hw_ops = hw_perf_counter_init(counter);
+ }
if (!hw_ops) {
kfree(counter);
@@ -2175,6 +2189,28 @@ perf_set_overcommit(struct sysdev_class *class, const char *buf, size_t count)
return count;
}
+static ssize_t perf_show_strict(struct sysdev_class *class, char *buf)
+{
+ return sprintf(buf, "%d\n", perf_counters_strict);
+}
+
+static ssize_t
+perf_set_strict(struct sysdev_class *class, const char *buf, size_t count)
+{
+ unsigned long val;
+ int err;
+
+ err = strict_strtoul(buf, 10, &val);
+ if (err)
+ return err;
+ if (val > 1)
+ return -EINVAL;
+
+ perf_counters_strict = val;
+
+ return count;
+}
+
static SYSDEV_CLASS_ATTR(
reserve_percpu,
0644,
@@ -2189,9 +2225,17 @@ static SYSDEV_CLASS_ATTR(
perf_set_overcommit
);
+static SYSDEV_CLASS_ATTR(
+ restrict_kernel_events,
+ 0644,
+ perf_show_strict,
+ perf_set_strict
+ );
+
static struct attribute *perfclass_attrs[] = {
&attr_reserve_percpu.attr,
&attr_overcommit.attr,
+ &attr_restrict_kernel_events.attr,
NULL
};
--
1.5.6.3
--
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