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[92.238.24.70]) by smtp.googlemail.com with ESMTPSA id a640c23a62f3a-a9957d955f8sm99206066b.74.2024.10.07.03.00.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Oct 2024 03:00:48 -0700 (PDT) Message-ID: <6181060a-ae36-4d0f-bfe0-c1e5c8a8ab3c@gmail.com> Date: Mon, 7 Oct 2024 11:00:46 +0100 Precedence: bulk X-Mailing-List: imx@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH][next] clk: imx: pll14xx: Fix potential integer overflow on multiplication To: Dan Carpenter Cc: Abel Vesa , Peng Fan , Michael Turquette , Stephen Boyd , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , linux-clk@vger.kernel.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org References: <20241007084840.1167527-1-colin.i.king@gmail.com> <3e0def9f-ebb6-4171-9395-1da118b0ea29@stanley.mountain> Content-Language: en-US From: "Colin King (gmail)" In-Reply-To: <3e0def9f-ebb6-4171-9395-1da118b0ea29@stanley.mountain> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 07/10/2024 10:54, Dan Carpenter wrote: > On Mon, Oct 07, 2024 at 09:48:40AM +0100, Colin Ian King wrote: >> The calculation of fout is using int multiplication and assigning >> the result to a u64, this can potentially overflow if the int variable >> mdiv is too large. Fix this by making the 65536 a u64 value to ensure a >> u64 multiplication is being performed to avoid the overflow. >> >> Fixes: 53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation") >> Signed-off-by: Colin Ian King > > mdiv is always clamped in then 0-1023 range by one of these: > > mdiv = FIELD_GET(MDIV_MASK, pll_div_ctl0); > mdiv = clamp(mdiv, 64, 1023); > > so it can't overflow and the Fixes tag is unnecessary. Good point. > > I think the reason why "fout" is declared as a u64 is because we were worried > that on 32 bit systems the "fout *=" operation could overflow. That looks > reasonable to me. Yes, that makes perfect sense. NAK my patch. Apologies for the noise. Colin > > regards, > dan carpenter >