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

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

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