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

[Heiko Carstens]

On Tue, Aug 25, 2026 at 05:08:08PM +0200, Ilya Leoshkevich 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.
> 
> Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> ---
>  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;

Hm, I guess the comment refers to a different implementation than the
kernel internal one? Since isprint() (see include/linux/ctype.h) is
true for exactly the range you open-coded, as far as I can tell.

Furthermore kernel command line parsing also allows for all sorts of
spaces, tabs, and line feeds (see e.g. next_arg()). So I guess the
above should be changed (and shortened :) ) to something like:

static inline int has_nonprintable_char(const char *str)
{
	for (int i = 0; str[i]; i++) {
		if (isprint(str[i]) || isspace(str[i]))
			return 1;
	}
	return 0;
}