OPP: fix dev_pm_opp_find_bw_*() when bandwidth table not initialized

JIRA: https://issues.redhat.com/browse/RHEL-84805
CVE: CVE-2024-58068

commit b44b9bc
Author: Neil Armstrong <[email protected]>
Date:   Tue Dec 3 09:13:00 2024 +0100

    OPP: fix dev_pm_opp_find_bw_*() when bandwidth table not initialized

    If a driver calls dev_pm_opp_find_bw_ceil/floor() the retrieve bandwidth
    from the OPP table but the bandwidth table was not created because the
    interconnect properties were missing in the OPP consumer node, the
    kernel will crash with:

    Unable to handle kernel NULL pointer dereference at virtual address 0000000000000004
    ...
    pc : _read_bw+0x8/0x10
    lr : _opp_table_find_key+0x9c/0x174
    ...
    Call trace:
      _read_bw+0x8/0x10 (P)
      _opp_table_find_key+0x9c/0x174 (L)
      _find_key+0x98/0x168
      dev_pm_opp_find_bw_ceil+0x50/0x88
    ...

    In order to fix the crash, create an assert function to check
    if the bandwidth table was created before trying to get a
    bandwidth with _read_bw().

    Fixes: add1dc0 ("OPP: Use generic key finding helpers for bandwidth key")
    Signed-off-by: Neil Armstrong <[email protected]>
    Signed-off-by: Viresh Kumar <[email protected]>

Signed-off-by: Jared Kangas <[email protected]>

Author: rh-jkangas

drivers/opp/core.c

@@ -116,6 +116,15 @@ static bool assert_clk_index(struct opp_table *opp_table,
 	return opp_table->clk_count > index;
 }
 
+/*
+ * Returns true if bandwidth table is large enough to contain the bandwidth index.
+ */
+static bool assert_bandwidth_index(struct opp_table *opp_table,
+				   unsigned int index)
+{
+	return opp_table->path_count > index;
+}
+
 /**
  * dev_pm_opp_get_voltage() - Gets the voltage corresponding to an opp
  * @opp:	opp for which voltage has to be returned for
@@ -890,7 +899,8 @@ struct dev_pm_opp *dev_pm_opp_find_bw_ceil(struct device *dev, unsigned int *bw,
 	unsigned long temp = *bw;
 	struct dev_pm_opp *opp;
 
-	opp = _find_key_ceil(dev, &temp, index, true, _read_bw, NULL);
+	opp = _find_key_ceil(dev, &temp, index, true, _read_bw,
+			     assert_bandwidth_index);
 	*bw = temp;
 	return opp;
 }
@@ -921,7 +931,8 @@ struct dev_pm_opp *dev_pm_opp_find_bw_floor(struct device *dev,
 	unsigned long temp = *bw;
 	struct dev_pm_opp *opp;
 
-	opp = _find_key_floor(dev, &temp, index, true, _read_bw, NULL);
+	opp = _find_key_floor(dev, &temp, index, true, _read_bw,
+			      assert_bandwidth_index);
 	*bw = temp;
 	return opp;
 }