x86/boot: validate console=uart8250 baud rate to avoid early boot hang

[PATCH] x86/boot: validate console=uart8250 baud rate to avoid early boot hang

Posted by Thorsten Blum 4 weeks ago

When the baud rate is empty, 0, invalid, or overflows to 0 when stored
as an int, the system will hang during early boot because of a division
by zero in early_serial_init().

Fall back to DEFAULT_BAUD when the resulting baud rate is 0 to prevent
an early system hang.

Fixes: ce0aa5dd20e4 ("x86, setup: Make the setup code also accept console=uart8250")
Cc: stable@vger.kernel.org
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 arch/x86/boot/early_serial_console.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/early_serial_console.c b/arch/x86/boot/early_serial_console.c
index 023bf1c3de8b..28a887af430d 100644
--- a/arch/x86/boot/early_serial_console.c
+++ b/arch/x86/boot/early_serial_console.c
@@ -117,7 +117,7 @@ static unsigned int probe_baud(int port)
 static void parse_console_uart8250(void)
 {
 	char optstr[64], *options;
-	int baud = DEFAULT_BAUD;
+	int baud;
 	int port = 0;
 
 	/*
@@ -136,9 +136,11 @@ static void parse_console_uart8250(void)
 	else
 		return;
 
-	if (options && (options[0] == ','))
-		baud = simple_strtoull(options + 1, &options, 0);
-	else
+	if (options && (options[0] == ',')) {
+		baud = simple_strtoull(options + 1, NULL, 0);
+		if (!baud)
+			baud = DEFAULT_BAUD;
+	} else
 		baud = probe_baud(port);
 
 	if (port)

Re: [PATCH] x86/boot: validate console=uart8250 baud rate to avoid early boot hang

Posted by Thorsten Blum 2 weeks, 1 day ago

On Thu, May 14, 2026 at 04:30:15PM +0200, Thorsten Blum wrote:
> When the baud rate is empty, 0, invalid, or overflows to 0 when stored
> as an int, the system will hang during early boot because of a division
> by zero in early_serial_init().
> 
> Fall back to DEFAULT_BAUD when the resulting baud rate is 0 to prevent
> an early system hang.
> 
> Fixes: ce0aa5dd20e4 ("x86, setup: Make the setup code also accept console=uart8250")
> Cc: stable@vger.kernel.org
> Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
> ---
>  arch/x86/boot/early_serial_console.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/boot/early_serial_console.c b/arch/x86/boot/early_serial_console.c
> index 023bf1c3de8b..28a887af430d 100644
> --- a/arch/x86/boot/early_serial_console.c
> +++ b/arch/x86/boot/early_serial_console.c
> @@ -117,7 +117,7 @@ static unsigned int probe_baud(int port)
>  static void parse_console_uart8250(void)
>  {
>  	char optstr[64], *options;
> -	int baud = DEFAULT_BAUD;
> +	int baud;
>  	int port = 0;
>  
>  	/*
> @@ -136,9 +136,11 @@ static void parse_console_uart8250(void)
>  	else
>  		return;
>  
> -	if (options && (options[0] == ','))
> -		baud = simple_strtoull(options + 1, &options, 0);
> -	else
> +	if (options && (options[0] == ',')) {
> +		baud = simple_strtoull(options + 1, NULL, 0);
> +		if (!baud)
> +			baud = DEFAULT_BAUD;
> +	} else
>  		baud = probe_baud(port);
>  
>  	if (port)

Gentle ping?

I also tested this and verified that it works.