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Subject: [PATCH v6 09/10] drivers/perf: open access for CAP_PERFMON privileged
 process
From:   Alexey Budankov <alexey.budankov@linux.intel.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
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        Michael Ellerman <mpe@ellerman.id.au>,
        "james.bottomley@hansenpartnership.com" 
        <james.bottomley@hansenpartnership.com>,
        Serge Hallyn <serge@hallyn.com>, Will Deacon <will@kernel.org>,
        Robert Richter <rric@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>
Cc:     "intel-gfx@lists.freedesktop.org" <intel-gfx@lists.freedesktop.org>,
        Jiri Olsa <jolsa@redhat.com>, Andi Kleen <ak@linux.intel.com>,
        Stephane Eranian <eranian@google.com>,
        Igor Lubashev <ilubashe@akamai.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Namhyung Kim <namhyung@kernel.org>,
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References: <74d524ab-ac11-a7b8-1052-eba10f117e09@linux.intel.com>
Organization: Intel Corp.
Message-ID: <f2877038-da53-f981-4ddb-4e6c1c27c60f@linux.intel.com>
Date:   Tue, 28 Jan 2020 09:13:38 +0300
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Open access to monitoring for CAP_PERFMON privileged process.
Providing the access under CAP_PERFMON capability singly, without the
rest of CAP_SYS_ADMIN credentials, excludes chances to misuse the
credentials and makes operation more secure.

CAP_PERFMON implements the principal of least privilege for performance
monitoring and observability operations (POSIX IEEE 1003.1e 2.2.2.39 principle
of least privilege: A security design principle that states that a process
or program be granted only those privileges (e.g., capabilities) necessary
to accomplish its legitimate function, and only for the time that such
privileges are actually required)

For backward compatibility reasons access to the monitoring remains open
for CAP_SYS_ADMIN privileged processes but CAP_SYS_ADMIN usage for secure
monitoring is discouraged with respect to CAP_PERFMON capability.

Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
---
 drivers/perf/arm_spe_pmu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
index 4e4984a55cd1..5dff81bc3324 100644
--- a/drivers/perf/arm_spe_pmu.c
+++ b/drivers/perf/arm_spe_pmu.c
@@ -274,7 +274,7 @@ static u64 arm_spe_event_to_pmscr(struct perf_event *event)
 	if (!attr->exclude_kernel)
 		reg |= BIT(SYS_PMSCR_EL1_E1SPE_SHIFT);
 
-	if (IS_ENABLED(CONFIG_PID_IN_CONTEXTIDR) && capable(CAP_SYS_ADMIN))
+	if (IS_ENABLED(CONFIG_PID_IN_CONTEXTIDR) && perfmon_capable())
 		reg |= BIT(SYS_PMSCR_EL1_CX_SHIFT);
 
 	return reg;
@@ -700,7 +700,7 @@ static int arm_spe_pmu_event_init(struct perf_event *event)
 		return -EOPNOTSUPP;
 
 	reg = arm_spe_event_to_pmscr(event);
-	if (!capable(CAP_SYS_ADMIN) &&
+	if (!perfmon_capable() &&
 	    (reg & (BIT(SYS_PMSCR_EL1_PA_SHIFT) |
 		    BIT(SYS_PMSCR_EL1_CX_SHIFT) |
 		    BIT(SYS_PMSCR_EL1_PCT_SHIFT))))
-- 
2.20.1