bus: arm-ccn: Do not attempt to configure XPs for cycle counter

commit b7c1beb278e8e3dc664ed3df3fc786db126120a9 upstream.

Fuzzing the CCN perf driver revealed a small but definitely dangerous
mistake in the event setup code. When a cycle counter is requested, the
driver should not reconfigure the events bus at all, otherwise it will
corrupt (in most but the simplest cases) its configuration and may end
up accessing XP array out of its bounds and corrupting control
registers.

Reported-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/bus/arm-ccn.c b/drivers/bus/arm-ccn.c
index 27f9d0587d4a67ec70d3dcb4d8ea45dcb6e2f567..0c22a03c9e57fa02bd8053fa7a64d77c7e4ea875 100644 (file)
--- a/drivers/bus/arm-ccn.c
+++ b/drivers/bus/arm-ccn.c
@@ -895,6 +895,10 @@ static void arm_ccn_pmu_xp_dt_config(struct perf_event *event, int enable)
        struct arm_ccn_component *xp;
        u32 val, dt_cfg;
 
+       /* Nothing to do for cycle counter */
+       if (hw->idx == CCN_IDX_PMU_CYCLE_COUNTER)
+               return;
+
        if (CCN_CONFIG_TYPE(event->attr.config) == CCN_TYPE_XP)
                xp = &ccn->xp[CCN_CONFIG_XP(event->attr.config)];
        else