linux-kernel - [PATCH v2 2/2] OPP: fix dev_pm_opp_find_bw_*() when bandwidth table not initialized

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Message-Id: <20241129-topic-opp-fix-assert-index-check-v2-2-386b2dcbb9a6@linaro.org>
Date: Fri, 29 Nov 2024 16:06:25 +0100
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>, 
 Stephen Boyd <sboyd@...nel.org>, 
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Viresh Kumar <viresh.kumar@...aro.org>, linux-pm@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Neil Armstrong <neil.armstrong@...aro.org>
Subject: [PATCH v2 2/2] 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: add1dc094a74 ("OPP: Use generic key finding helpers for bandwidth key")
Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
---
 drivers/opp/core.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/opp/core.c b/drivers/opp/core.c
index 52c6a45ceb7479c3ef0ed97ab43a37546d695c7f..c7d16b2c5110089aeb35012be1dc35dfd209963e 100644
--- a/drivers/opp/core.c
+++ b/drivers/opp/core.c
@@ -114,6 +114,14 @@ static bool assert_clk_index(struct opp_table *opp_table, int index)
 	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, int index)
+{
+	return opp_table->path_count > index;
+}
+
 /**
  * dev_pm_opp_get_bw() - Gets the bandwidth corresponding to an opp
  * @opp:	opp for which bandwidth has to be returned for
@@ -913,7 +921,8 @@ 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;
 }
@@ -944,7 +953,8 @@ 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;
 }

-- 
2.34.1