[PATCH v3 0/2] s390: Warn if kernel command line contains non-printable EBCDIC

[PATCH v3 0/2] s390: Warn if kernel command line contains non-printable EBCDIC

[Ilya Leoshkevich]

v2: https://lore.kernel.org/all/20260826150702.949956-1-iii@linux.ibm.com/
v2 -> v3: Check whether source EBCDIC characters are printable
          (David, Heiko).

v1: https://lore.kernel.org/all/20260825150840.537653-1-iii@linux.ibm.com/
v1 -> v2: Account for newlines (Heiko).
          Minor stylistic improvements: inline int i, bool return type,
          comment modality.

Hi,

This series adds a warning for unintentional EBCDIC -> ASCII kernel
command line translations. Patch 1 adds EBCDIC character classes.
Patch 2 uses them for determining whether the command line is
printable.

Best regards,
Ilya

Ilya Leoshkevich (2):
  s390/ebcdic: Add character classes for the invariant subset of EBCDIC
  s390: Warn if kernel command line contains non-printable EBCDIC
    characters

 arch/s390/boot/ipl_parm.c      | 13 ++++++++++-
 arch/s390/include/asm/ebcdic.h |  5 +++++
 arch/s390/kernel/ebcdic.c      | 40 +++++++++++++++++++++++++++++++++-
 3 files changed, 56 insertions(+), 2 deletions(-)

-- 
2.55.0

[PATCH v3 1/2] s390/ebcdic: Add character classes for the invariant subset of EBCDIC

[Ilya Leoshkevich]

Add _ctypes-like array for the invariant subset of EBCDIC, which
consists of characters that should have the same assignments on all
EBCDIC code pages that use the Latin alphabet [1].

[1] https://en.wikipedia.org/wiki/EBCDIC#Code_page_layout

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 arch/s390/include/asm/ebcdic.h |  5 +++++
 arch/s390/kernel/ebcdic.c      | 40 +++++++++++++++++++++++++++++++++-
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/arch/s390/include/asm/ebcdic.h b/arch/s390/include/asm/ebcdic.h
index 7164cb6584355..9b7e3a58ca738 100644
--- a/arch/s390/include/asm/ebcdic.h
+++ b/arch/s390/include/asm/ebcdic.h
@@ -10,6 +10,7 @@
 #ifndef _EBCDIC_H
 #define _EBCDIC_H
 
+#include <linux/ctype.h>
 #include <linux/types.h>
 
 extern __u8 _ascebc_500[256];   /* ASCII -> EBCDIC 500 conversion table */
@@ -18,6 +19,10 @@ extern __u8 _ascebc[256];   /* ASCII -> EBCDIC conversion table */
 extern __u8 _ebcasc[256];   /* EBCDIC -> ASCII conversion table */
 extern __u8 _ebc_tolower[256]; /* EBCDIC -> lowercase */
 extern __u8 _ebc_toupper[256]; /* EBCDIC -> uppercase */
+extern const __u8 _ebctype_inv[256]; /* EBCDIC -> character classes */
+
+#define __ismask_ebc_inv(x) (_ebctype_inv[(int)(unsigned char)(x)])
+#define isprint_ebc_inv(c) ((__ismask_ebc_inv(c)&(_P|_U|_L|_D|_SP)) != 0)
 
 static inline void
 codepage_convert(const __u8 *codepage, volatile char *addr, unsigned long nr)
diff --git a/arch/s390/kernel/ebcdic.c b/arch/s390/kernel/ebcdic.c
index 0e51fa537262b..15cbb0b42aa6e 100644
--- a/arch/s390/kernel/ebcdic.c
+++ b/arch/s390/kernel/ebcdic.c
@@ -392,10 +392,48 @@ __u8 _ebc_toupper[256] =
 	0xF8, 0xF9, 0xFA, 0xFB, 0xFC, 0xFD, 0xFE, 0xFF
 };
 
+/*
+ * EBCDIC -> character classes
+ */
+const __u8 _ebctype_inv[256] = {
+	_C,     _C,    _C,    _C,    _C,    _C|_S, _C,    _C,	/* 0x00-0x07 */
+	_C,     _C,    _C,    _C|_S, _C|_S, _C|_S, _C,    _C,	/* 0x08-0x0f */
+	_C,     _C,    _C,    _C,    _C,    _C|_S, _C,    _C,	/* 0x10-0x17 */
+	_C,     _C,    _C,    _C,    _C,    _C,    _C,    _C,	/* 0x18-0x1f */
+	_C,     _C,    _C,    _C,    _C,    _C|_S, _C,    _C,	/* 0x20-0x27 */
+	_C,     _C,    _C,    _C,    _C,    _C,    _C,    _C,	/* 0x28-0x2f */
+	0,      0,     _C,    _C,    _C,    _C,    _C,    _C,	/* 0x30-0x37 */
+	_C,     _C,    _C,    _C,    _C,    _C,    0,     _C,	/* 0x38-0x3f */
+	_S|_SP, 0,     0,     0,     0,     0,     0,     0,	/* 0x40-0x47 */
+	0,      0,     _P,    _P,    _P,    _P,    _P,    _P,	/* 0x48-0x4f */
+	_P,     0,     0,     0,     0,     0,     0,     0,	/* 0x50-0x57 */
+	0,      0,     _P,    _P,    _P,    _P,    _P,    _P,	/* 0x58-0x5f */
+	_P,     _P,    0,     0,     0,     0,     0,     0,	/* 0x60-0x67 */
+	0,      0,     _P,    _P,    _P,    _P,    _P,    _P,	/* 0x68-0x6f */
+	0,      0,     0,     0,     0,     0,     0,     0,	/* 0x70-0x77 */
+	0,      _P,    _P,    _P,    _P,    _P,    _P,    _P,	/* 0x78-0x7f */
+	0,      _L|_X, _L|_X, _L|_X, _L|_X, _L|_X, _L|_X, _L,	/* 0x80-0x87 */
+	_L,     _L,    0,     0,     0,     0,     0,     _P,	/* 0x88-0x8f */
+	0,      _L,    _L,    _L,    _L,    _L,    _L,    _L,	/* 0x90-0x97 */
+	_L,     _L,    0,     0,     0,     0,     0,     0,	/* 0x98-0x9f */
+	0,      _P,    _L,    _L,    _L,    _L,    _L,    _L,	/* 0xa0-0xa7 */
+	_L,     _L,    0,     0,     0,     0,     0,     0,	/* 0xa8-0xaf */
+	_P,     0,     0,     0,     0,     0,     0,     0,	/* 0xb0-0xb7 */
+	0,      0,     _P,    _P,    0,     0,     0,     0,	/* 0xb8-0xbf */
+	_P,     _U|_X, _U|_X, _U|_X, _U|_X, _U|_X, _U|_X, _U,	/* 0xc0-0xc7 */
+	_U,     _U,    0,     0,     0,     0,     0,     0,	/* 0xc8-0xcf */
+	_P,     _U,    _U,    _U,    _U,    _U,    _U,    _U,	/* 0xd0-0xd7 */
+	_U,     _U,    0,     0,     0,     0,     0,     0,	/* 0xd8-0xdf */
+	_P,     0,     _U,    _U,    _U,    _U,    _U,    _U,	/* 0xe0-0xe7 */
+	_U,     _U,    0,     0,     0,     0,     0,     0,	/* 0xe8-0xef */
+	_D,     _D,    _D,    _D,    _D,    _D,    _D,    _D,	/* 0xf0-0xf7 */
+	_D,     _D,    0,     0,     0,     0,     0,     _C,	/* 0xf8-0xff */
+};
+
 EXPORT_SYMBOL(_ascebc_500);
 EXPORT_SYMBOL(_ebcasc_500);
 EXPORT_SYMBOL(_ascebc);
 EXPORT_SYMBOL(_ebcasc);
 EXPORT_SYMBOL(_ebc_tolower);
 EXPORT_SYMBOL(_ebc_toupper);
-
+EXPORT_SYMBOL(_ebctype_inv);
-- 
2.55.0

[PATCH v3 2/2] 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.

The current solution deliberately makes the following tradeoffs:

* Do not make this a hard failure, there may be a very small number
  of users who put characters with diacritics on their EBCDIC-encoded
  command lines.
* Do not use heuristics with arbitrary thresholds, these may fail
  intermittently on, e.g., punctuation-heavy command lines, and having
  to tune thresholds in subsequent patches is not desirable.
* Use the invariant subset of EBCDIC to determine whether characters
  are printable, the vast majority of command lines will contain
  characters from this subset.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 arch/s390/boot/ipl_parm.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/s390/boot/ipl_parm.c b/arch/s390/boot/ipl_parm.c
index 6bc950b92be76..24573307263ca 100644
--- a/arch/s390/boot/ipl_parm.c
+++ b/arch/s390/boot/ipl_parm.c
@@ -173,12 +173,23 @@ static inline int has_ebcdic_char(const char *str)
 	return 0;
 }
 
+static inline bool has_nonprintable_ebcdic_char(const char *str)
+{
+	for (; *str; str++)
+		if (!isprint_ebc_inv(*str))
+			return true;
+	return false;
+}
+
 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)) {
+		if (has_nonprintable_ebcdic_char(parmarea.command_line))
+			boot_warn("Kernel command line was treated as EBCDIC, but contains non-printable characters\n");
 		EBCASC(parmarea.command_line, COMMAND_LINE_SIZE);
+	}
 	/* copy arch command line */
 	strscpy(early_command_line, strim(parmarea.command_line));
 
-- 
2.55.0