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

[Ilya Leoshkevich <iii@linux.ibm.com>]

On 8/26/26 11:29, Heiko Carstens wrote:
> 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@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;
> 
> 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.

Unfortunately isprint() matches some extra ASCII upper-half characters,
e.g.:

   const unsigned char _ctype[] = {
   [...]
   _P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,        /* 176-191 */

> 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:

I completely forgot about newlines, thanks!

> 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;
> }