perf/x86: Fix possible Spectre-v1 indexing for x86_pmu::event_map()

> arch/x86/events/intel/cstate.c:307 cstate_pmu_event_init() warn: potential spectre issue 'pkg_msr' (local cap)
> arch/x86/events/intel/core.c:337 intel_pmu_event_map() warn: potential spectre issue 'intel_perfmon_event_map'
> arch/x86/events/intel/knc.c:122 knc_pmu_event_map() warn: potential spectre issue 'knc_perfmon_event_map'
> arch/x86/events/intel/p4.c:722 p4_pmu_event_map() warn: potential spectre issue 'p4_general_events'
> arch/x86/events/intel/p6.c:116 p6_pmu_event_map() warn: potential spectre issue 'p6_perfmon_event_map'
> arch/x86/events/amd/core.c:132 amd_pmu_event_map() warn: potential spectre issue 'amd_perfmon_event_map'

Userspace controls @attr, sanitize @attr->config before passing it on
to x86_pmu::event_map().

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <stable@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/events/core.c

@@ -27,6 +27,7 @@
 #include <linux/cpu.h>
 #include <linux/bitops.h>
 #include <linux/device.h>
+#include <linux/nospec.h>
 
 #include <asm/apic.h>
 #include <asm/stacktrace.h>
@@ -424,6 +425,8 @@ int x86_setup_perfctr(struct perf_event *event)
 	if (attr->config >= x86_pmu.max_events)
 		return -EINVAL;
 
+	attr->config = array_index_nospec((unsigned long)attr->config, x86_pmu.max_events);
+
 	/*
 	 * The generic map:
 	 */