From:   Sergio Paracuellos <sergio.paracuellos@gmail.com>
To:     linux-clk@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, sboyd@kernel.org,
        mturquette@baylibre.com, matthias.bgg@gmail.com
Subject: [PATCH] clk: ralink: fix 'mt7621_gate_is_enabled()' function
Date:   Mon,  6 Feb 2023 09:33:05 +0100
Message-Id: <20230206083305.147582-1-sergio.paracuellos@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Compiling clock driver with CONFIG_UBSAN enabled shows the following trace:

UBSAN: shift-out-of-bounds in drivers/clk/ralink/clk-mt7621.c:121:15
shift exponent 131072 is too large for 32-bit type 'long unsigned int'
CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.15.86 #0
Stack : ...

Call Trace:
[<80009a58>] show_stack+0x38/0x118
[<8045ce04>] dump_stack_lvl+0x60/0x80
[<80458868>] ubsan_epilogue+0x10/0x54
[<804590e0>] __ubsan_handle_shift_out_of_bounds+0x118/0x190
[<804c9a10>] mt7621_gate_is_enabled+0x98/0xa0
[<804bb774>] clk_core_is_enabled+0x34/0x90
[<80aad73c>] clk_disable_unused_subtree+0x98/0x1e4
[<80aad6d4>] clk_disable_unused_subtree+0x30/0x1e4
[<80aad6d4>] clk_disable_unused_subtree+0x30/0x1e4
[<80aad900>] clk_disable_unused+0x78/0x120
[<80002030>] do_one_initcall+0x54/0x1f0
[<80a922a4>] kernel_init_freeable+0x280/0x31c
[<808047c4>] kernel_init+0x20/0x118
[<80003e58>] ret_from_kernel_thread+0x14/0x1c

Shifting a value (131032) larger than the type (32 bit unsigned integer)
is undefined behaviour in C.

The problem is in 'mt7621_gate_is_enabled()' function which is using the
'BIT()' kernel macro with the bit index for the clock gate to check if the
bit is set. When the clock gates structure is created driver is already
setting 'bit_idx' using 'BIT()' macro, so we are wrongly applying an extra
'BIT()' mask here. Removing it solve the problem and makes this function
correct. However when clock gating is correctly working, the kernel starts
disabling those clocks that are not requested. Some drivers for this SoC
are older than this clock driver itself. So to avoid the kernel to disable
clocks that have been enabled until now, we must apply 'CLK_IS_CRITICAL'
flag on gates initialization code.

Fixes: 48df7a26f470 ("clk: ralink: add clock driver for mt7621 SoC")
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
---
 drivers/clk/ralink/clk-mt7621.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/ralink/clk-mt7621.c b/drivers/clk/ralink/clk-mt7621.c
index 99256659dd96..d95a33293b0a 100644
--- a/drivers/clk/ralink/clk-mt7621.c
+++ b/drivers/clk/ralink/clk-mt7621.c
@@ -121,7 +121,7 @@ static int mt7621_gate_is_enabled(struct clk_hw *hw)
 	if (regmap_read(sysc, SYSC_REG_CLKCFG1, &val))
 		return 0;
 
-	return val & BIT(clk_gate->bit_idx);
+	return val & clk_gate->bit_idx;
 }
 
 static const struct clk_ops mt7621_gate_ops = {
@@ -133,8 +133,14 @@ static const struct clk_ops mt7621_gate_ops = {
 static int mt7621_gate_ops_init(struct device *dev,
 				struct mt7621_gate *sclk)
 {
+	/*
+	 * There are drivers for this SoC that are older
+	 * than clock driver and are not prepared for the clock.
+	 * We don't want the kernel to disable anything so we
+	 * add CLK_IS_CRITICAL flag here.
+	 */
 	struct clk_init_data init = {
-		.flags = CLK_SET_RATE_PARENT,
+		.flags = CLK_SET_RATE_PARENT | CLK_IS_CRITICAL,
 		.num_parents = 1,
 		.parent_names = &sclk->parent_name,
 		.ops = &mt7621_gate_ops,
-- 
2.25.1