perf/x86/msr: Fix possible Spectre-v1 indexing in the MSR driver

commit 06ce6e9b6d6c09d4129c6e24a1314a395d816c10 upstream.

> arch/x86/events/msr.c:178 msr_event_init() warn: potential spectre issue 'msr' (local cap)

Userspace controls @attr, sanitize cfg (attr->config) before using it
to index an array.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/cpu/perf_event_msr.c b/arch/x86/kernel/cpu/perf_event_msr.c
index ec863b9a9f780c7507634353d64f9c2f76f1a0e1..067427384a63a93b39b9a45d096b3db87df8c33e 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event_msr.c
+++ b/arch/x86/kernel/cpu/perf_event_msr.c
@@ -1,4 +1,5 @@
 #include <linux/perf_event.h>
+#include <linux/nospec.h>
 
 enum perf_msr_id {
        PERF_MSR_TSC                    = 0,
@@ -115,9 +116,6 @@ static int msr_event_init(struct perf_event *event)
        if (event->attr.type != event->pmu->type)
                return -ENOENT;
 
-       if (cfg >= PERF_MSR_EVENT_MAX)
-               return -EINVAL;
-
        /* unsupported modes and filters */
        if (event->attr.exclude_user   ||
            event->attr.exclude_kernel ||
@@ -128,6 +126,11 @@ static int msr_event_init(struct perf_event *event)
            event->attr.sample_period) /* no sampling */
                return -EINVAL;
 
+       if (cfg >= PERF_MSR_EVENT_MAX)
+               return -EINVAL;
+
+       cfg = array_index_nospec((unsigned long)cfg, PERF_MSR_EVENT_MAX);
+
        if (!msr[cfg].attr)
                return -EINVAL;