Re: [PATCH] s390: Warn if kernel command line contains non-printable EBCDIC characters

[David Laight <david.laight.linux@gmail.com>]

On Tue, 25 Aug 2026 17:08:08 +0200
Ilya Leoshkevich <iii@linux.ibm.com> wrote:

> Users may accidentally add multi-byte UTF-8 characters to zipl.conf
> parmline, for example, by copying snippets containing non-breaking
> spaces (\xC2\xA0) from web pages.
> 
> The kernel will then interpret the entire command line as EBCDIC,
> making it unusable. Distinguish this situation from the legitimate
> EBCDIC conversion by looking for non-printable characters and issue
> a warning.

Would it be better to check for the entire line being printable ebcdic?
All of EBCDIC a-zA-Z0-9 have the 0x80 bit set and most of 0x20..0x7f
are invalid or control characters (or punctuation).

David

> 
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>  arch/s390/boot/ipl_parm.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/boot/ipl_parm.c b/arch/s390/boot/ipl_parm.c
> index 6bc950b92be76..71c0c26d56bba 100644
> --- a/arch/s390/boot/ipl_parm.c
> +++ b/arch/s390/boot/ipl_parm.c
> @@ -173,12 +173,29 @@ static inline int has_ebcdic_char(const char *str)
>  	return 0;
>  }
>  
> +static inline int has_nonprintable_char(const char *str)
> +{
> +	int i;
> +
> +	for (i = 0; str[i]; i++) {
> +		unsigned char c = (unsigned char)str[i];
> +
> +		/* isprint() is Latin-1, and we need ASCII here */
> +		if (c < 0x20 || c > 0x7e)
> +			return 1;
> +	}
> +	return 0;
> +}
> +
>  void setup_boot_command_line(void)
>  {
>  	parmarea.command_line[COMMAND_LINE_SIZE - 1] = 0;
>  	/* convert arch command line to ascii if necessary */
> -	if (has_ebcdic_char(parmarea.command_line))
> +	if (has_ebcdic_char(parmarea.command_line)) {
>  		EBCASC(parmarea.command_line, COMMAND_LINE_SIZE);
> +		if (has_nonprintable_char(parmarea.command_line))
> +			boot_warn("Kernel command line was treated as EBCDIC, but contains non-printable characters\n");
> +	}
>  	/* copy arch command line */
>  	strscpy(early_command_line, strim(parmarea.command_line));
>