The patch titled
Subject: bug: move WARN_ON() "cut here" into exception handler
has been added to the -mm tree. Its filename is
bug-move-warn_on-cut-here-into-exception-handler.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/bug-move-warn_on-cut-here-into-exception-handler.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/bug-move-warn_on-cut-here-into-exception-handler.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Kees Cook <keescook@xxxxxxxxxxxx>
Subject: bug: move WARN_ON() "cut here" into exception handler
The original clean up of "cut here" missed the WARN_ON() case (that does
not have a printk message), which was fixed recently by adding an explicit
printk of "cut here". This had the downside of adding a printk() to every
WARN_ON() caller, which reduces the utility of using an instruction
exception to streamline the resulting code. By making this a new BUGFLAG,
all of these can be removed and "cut here" can be handled by the exception
handler.
This was very pronounced on PowerPC, but the effect can be seen on x86 as
well. The resulting text size of a defconfig build shows some small
savings from this patch:
text data bss dec hex filename
19691167 5134320 1646664 26472151 193eed7 vmlinux.before
19676362 5134260 1663048 26473670 193f4c6 vmlinux.after
This change also opens the door for creating something like BUG_MSG(),
where a custom printk() before issuing BUG(), without confusing the "cut
here" line.
Link: http://lkml.kernel.org/r/201908200943.601DD59DCE@keescook
Fixes: 6b15f678fb7d ("include/asm-generic/bug.h: fix "cut here" for WARN_ON for __WARN_TAINT architectures")
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reported-by: Christophe Leroy <christophe.leroy@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxx>
Cc: Drew Davenport <ddavenport@xxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
Cc: Feng Tang <feng.tang@xxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab+samsung@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: YueHaibing <yuehaibing@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/asm-generic/bug.h | 8 +++-----
lib/bug.c | 11 +++++++++--
2 files changed, 12 insertions(+), 7 deletions(-)
--- a/include/asm-generic/bug.h~bug-move-warn_on-cut-here-into-exception-handler
+++ a/include/asm-generic/bug.h
@@ -10,6 +10,7 @@
#define BUGFLAG_WARNING (1 << 0)
#define BUGFLAG_ONCE (1 << 1)
#define BUGFLAG_DONE (1 << 2)
+#define BUGFLAG_NO_CUT_HERE (1 << 3) /* CUT_HERE already sent */
#define BUGFLAG_TAINT(taint) ((taint) << 8)
#define BUG_GET_TAINT(bug) ((bug)->flags >> 8)
#endif
@@ -86,13 +87,10 @@ void warn_slowpath_fmt(const char *file,
warn_slowpath_fmt(__FILE__, __LINE__, taint, arg)
#else
extern __printf(1, 2) void __warn_printk(const char *fmt, ...);
-#define __WARN() do { \
- printk(KERN_WARNING CUT_HERE); \
- __WARN_FLAGS(BUGFLAG_TAINT(TAINT_WARN)); \
- } while (0)
+#define __WARN() __WARN_FLAGS(BUGFLAG_TAINT(TAINT_WARN))
#define __WARN_printf(taint, arg...) do { \
__warn_printk(arg); \
- __WARN_FLAGS(BUGFLAG_TAINT(taint)); \
+ __WARN_FLAGS(BUGFLAG_NO_CUT_HERE | BUGFLAG_TAINT(taint));\
} while (0)
#define WARN_ON_ONCE(condition) ({ \
int __ret_warn_on = !!(condition); \
--- a/lib/bug.c~bug-move-warn_on-cut-here-into-exception-handler
+++ a/lib/bug.c
@@ -181,6 +181,15 @@ enum bug_trap_type report_bug(unsigned l
}
}
+ /*
+ * BUG() and WARN_ON() families don't print a custom debug message
+ * before triggering the exception handler, so we must add the
+ * "cut here" line now. WARN() issues its own "cut here" before the
+ * extra debugging message it writes before triggering the handler.
+ */
+ if ((bug->flags & BUGFLAG_NO_CUT_HERE) == 0)
+ printk(KERN_DEFAULT CUT_HERE);
+
if (warning) {
/* this is a WARN_ON rather than BUG/BUG_ON */
__warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
@@ -188,8 +197,6 @@ enum bug_trap_type report_bug(unsigned l
return BUG_TRAP_TYPE_WARN;
}
- printk(KERN_DEFAULT CUT_HERE);
-
if (file)
pr_crit("kernel BUG at %s:%u!\n", file, line);
else
_
Patches currently in -mm which might be from keescook@xxxxxxxxxxxx are
strscpy-reject-buffer-sizes-larger-than-int_max.patch
bug-refactor-away-warn_slowpath_fmt_taint.patch
bug-rename-__warn_printf_taint-to-__warn_printf.patch
bug-consolidate-warn_slowpath_fmt-usage.patch
bug-lift-cut-here-out-of-__warn.patch
bug-clean-up-helper-macros-to-remove-__warn_taint.patch
bug-consolidate-__warn_flags-usage.patch
bug-move-warn_on-cut-here-into-exception-handler.patch
