linux-kernel - [PATCH v4] clk: mvebu: Prevent division by zero in clk_double_div_recalc

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Message-Id: <20240930104934.4342-1-adiupina@astralinux.ru>
Date: Mon, 30 Sep 2024 13:49:34 +0300
From: Alexandra Diupina <adiupina@...ralinux.ru>
To: Andrew Lunn <andrew@...n.ch>
Cc: Alexandra Diupina <adiupina@...ralinux.ru>,
	Gregory Clement <gregory.clement@...tlin.com>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-clk@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	lvc-project@...uxtesting.org
Subject: [PATCH v4] clk: mvebu: Prevent division by zero in clk_double_div_recalc_rate()

get_div() may return zero, so it is necessary to check
before calling DIV_ROUND_UP_ULL().

Return value of get_div() depends on reg1, reg2, shift1, shift2
fields of clk_double_div structure which are filled using the
PERIPH_DOUBLEDIV macro. This macro is called from the
PERIPH_CLK_FULL_DD and PERIPH_CLK_MUX_DD macros (the last 4 arguments).

It is not known exactly what values can be contained in the registers
at the addresses DIV_SEL0, DIV_SEL1, DIV_SEL2, so the final value of
div can be zero. Print an error message and return 0 in this case.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 8ca4746a78ab ("clk: mvebu: Add the peripheral clock driver for Armada 3700")
Signed-off-by: Alexandra Diupina <adiupina@...ralinux.ru>
---
v4: replace hw->init->name with clk_hw_get_name(hw)
v3: fix indentation
v2: added explanations to the commit message and printing 
of an error message when div==0
 drivers/clk/mvebu/armada-37xx-periph.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/mvebu/armada-37xx-periph.c b/drivers/clk/mvebu/armada-37xx-periph.c
index 13906e31bef8..2f0145a76f22 100644
--- a/drivers/clk/mvebu/armada-37xx-periph.c
+++ b/drivers/clk/mvebu/armada-37xx-periph.c
@@ -343,7 +343,12 @@ static unsigned long clk_double_div_recalc_rate(struct clk_hw *hw,
 	div = get_div(double_div->reg1, double_div->shift1);
 	div *= get_div(double_div->reg2, double_div->shift2);
 
-	return DIV_ROUND_UP_ULL((u64)parent_rate, div);
+	if (!div) {
+		pr_err("Can't recalculate the rate of clock %s\n", clk_hw_get_name(hw));
+		return 0;
+	} else {
+		return DIV_ROUND_UP_ULL((u64)parent_rate, div);
+	}
 }
 
 static const struct clk_ops clk_double_div_ops = {
-- 
2.30.2