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

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

[Ilya Leoshkevich]

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;
+	}
+	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));
 
-- 
2.55.0

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@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.

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;
}