linux-kernel - [PATCH 4.19 292/338] clk: Enforce that disjoints limits are invalid

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Date:   Thu, 14 Apr 2022 15:13:15 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Maxime Ripard <maxime@...no.tech>,
        Stephen Boyd <sboyd@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 292/338] clk: Enforce that disjoints limits are invalid

From: Maxime Ripard <maxime@...no.tech>

[ Upstream commit 10c46f2ea914202482d19cf80dcc9c321c9ff59b ]

If we were to have two users of the same clock, doing something like:

clk_set_rate_range(user1, 1000, 2000);
clk_set_rate_range(user2, 3000, 4000);

The second call would fail with -EINVAL, preventing from getting in a
situation where we end up with impossible limits.

However, this is never explicitly checked against and enforced, and
works by relying on an undocumented behaviour of clk_set_rate().

Indeed, on the first clk_set_rate_range will make sure the current clock
rate is within the new range, so it will be between 1000 and 2000Hz. On
the second clk_set_rate_range(), it will consider (rightfully), that our
current clock is outside of the 3000-4000Hz range, and will call
clk_core_set_rate_nolock() to set it to 3000Hz.

clk_core_set_rate_nolock() will then call clk_calc_new_rates() that will
eventually check that our rate 3000Hz rate is outside the min 3000Hz max
2000Hz range, will bail out, the error will propagate and we'll
eventually return -EINVAL.

This solely relies on the fact that clk_calc_new_rates(), and in
particular clk_core_determine_round_nolock(), won't modify the new rate
allowing the error to be reported. That assumption won't be true for all
drivers, and most importantly we'll break that assumption in a later
patch.

It can also be argued that we shouldn't even reach the point where we're
calling clk_core_set_rate_nolock().

Let's make an explicit check for disjoints range before we're doing
anything.

Signed-off-by: Maxime Ripard <maxime@...no.tech>
Link: https://lore.kernel.org/r/20220225143534.405820-4-maxime@cerno.tech
Signed-off-by: Stephen Boyd <sboyd@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/clk/clk.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index a9490c8e82a7..32606d1094fe 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -523,6 +523,24 @@ static void clk_core_get_boundaries(struct clk_core *core,
 		*max_rate = min(*max_rate, clk_user->max_rate);
 }

+static bool clk_core_check_boundaries(struct clk_core *core,
+				      unsigned long min_rate,
+				      unsigned long max_rate)
+{
+	struct clk *user;
+
+	lockdep_assert_held(&prepare_lock);
+
+	if (min_rate > core->max_rate || max_rate < core->min_rate)
+		return false;
+
+	hlist_for_each_entry(user, &core->clks, clks_node)
+		if (min_rate > user->max_rate || max_rate < user->min_rate)
+			return false;
+
+	return true;
+}
+
 void clk_hw_set_rate_range(struct clk_hw *hw, unsigned long min_rate,
 			   unsigned long max_rate)
 {
@@ -2066,6 +2084,11 @@ int clk_set_rate_range(struct clk *clk, unsigned long min, unsigned long max)
 	clk->min_rate = min;
 	clk->max_rate = max;

+	if (!clk_core_check_boundaries(clk->core, min, max)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
 	rate = clk_core_get_rate_nolock(clk->core);
 	if (rate < min || rate > max) {
 		/*
@@ -2094,6 +2117,7 @@ int clk_set_rate_range(struct clk *clk, unsigned long min, unsigned long max)
 		}
 	}

+out:
 	if (clk->exclusive_count)
 		clk_core_rate_protect(clk->core);

-- 
2.35.1