[PATCH] serial: amba-pl011: Fix divide by zero in pl011_console_get_options()

[PATCH] serial: amba-pl011: Fix divide by zero in pl011_console_get_options()

[Dan Carpenter]

When you boot QEMU with -kernel and don't set a baud rate the ibrd and
fbrd values are zero and so clkdiv is also zero.  It results in a divide
by zero.  Most of the time people don't notice because on
qemu-system-arm64 when you divide by zero the result is zero and
everything works.  However, if you enable UBSAN, then the divide by zero
leads to a crash and the boot fails.

Return early when clkdev is zero.  This leaves the baud rate set to its
default value of 38400.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan@cryspen.com>
---
 drivers/tty/serial/amba-pl011.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 7b1f99395f6c..a630d4751628 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2600,6 +2600,9 @@ static void pl011_console_get_options(struct uart_amba_port *uap, int *baud,
 		clkdiv = 64 * ibrd + fbrd;
 	}
 
+	if (!clkdiv)
+		return;
+
 	*baud = uap->port.uartclk * 4 / clkdiv;
 
 	if (uap->vendor->oversampling &&
-- 
2.53.0

Re: [PATCH] serial: amba-pl011: Fix divide by zero in pl011_console_get_options()

[sashiko-bot]

> When you boot QEMU with -kernel and don't set a baud rate the ibrd and
> fbrd values are zero and so clkdiv is also zero.  It results in a divide
> by zero.  Most of the time people don't notice because on
> qemu-system-arm64 when you divide by zero the result is zero and
> everything works.  However, if you enable UBSAN, then the divide by zero
> leads to a crash and the boot fails.
> 
> Return early when clkdev is zero.  This leaves the baud rate set to its
> default value of 38400.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Cc: stable@vger.kernel.org
> Signed-off-by: Dan Carpenter <dan@cryspen.com>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/6fdea544b2fb8f4226e296a952331cd42684474d.1794315353.git.dan@cryspen.com?part=1

Re: [PATCH] serial: amba-pl011: Fix divide by zero in pl011_console_get_options()

[Nicolai Buchwitz]

Hi Dan

On 11.11.2026 10:23, Dan Carpenter wrote:
> When you boot QEMU with -kernel and don't set a baud rate the ibrd and
> fbrd values are zero and so clkdiv is also zero.  It results in a 
> divide
> by zero.  Most of the time people don't notice because on
> qemu-system-arm64 when you divide by zero the result is zero and
> everything works.  However, if you enable UBSAN, then the divide by 
> zero
> leads to a crash and the boot fails.
> 
> Return early when clkdev is zero.  This leaves the baud rate set to its

nit: clkdiv

> default value of 38400.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Cc: stable@vger.kernel.org
> Signed-off-by: Dan Carpenter <dan@cryspen.com>

> [...]

Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>

Thanks,
Nicolai