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

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

On Wed, 26 Aug 2026 16:08:50 +0200
Ilya Leoshkevich <iii@linux.ibm.com> wrote:

> On 8/26/26 15:51, David Laight wrote:
> > 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  
> 
> I actually started with that, but this required introducing a new
> _ctype-like table (unfortunately it's not as simple as checking a
> couple ranges), so I decided against that and took a shortcut via
> ASCII.

Could you get the conversion function to return an error if it found
invalid EBCDIC characters?
If there is a single UTF8 character (eg non-breaking space) you really
want to treat the line as ASCII.
Actually you could count the number of characters with the 0x80 bit set.
If more than 1/2 assume EBCDIC (all of 0-9a-zA-Z have the bit set).

(I didn't realise anyone still used EBCDIC.
I guess the unix implementation(s) use ASCII (otherwise too much code
is broken) but the old IBM OS uses EBCDIC.
I worked for ICL for a while, their old 1900 series (from the early
1970s) used 6bit characters (4 in a 24bit word) that were ACSII codes
32-95. The replacement 2900 series (very late 1970s) used EBCDIC internally
(I guess because IBM used it...) but all the peripherals were ASCII.)

David

> 
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