Commit e427cd0a authored Feb 25, 2022 by Maxime Ripard Committed by Greg Kroah-Hartman Apr 15, 2022

clk: Enforce that disjoints limits are invalid



[ 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@cerno.tech>
Link: https://lore.kernel.org/r/20220225143534.405820-4-maxime@cerno.tech


Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 8a7462b5

drivers/clk/clk.c

+24 −0

Original line number	Diff line number	Diff line
		@@ -637,6 +637,24 @@ 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)
		{
		@@ -2306,6 +2324,11 @@ 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) {
		/*
		@@ -2334,6 +2357,7 @@ 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);