Commit a7bed27a authored Nov 17, 2017 by Kees Cook Committed by Linus Torvalds Nov 17, 2017

bug: fix "cut here" location for __WARN_TAINT architectures

Prior to v4.11, x86 used warn_slowpath_fmt() for handling WARN()s.
After WARN() was moved to using UD0 on x86, the warning text started
appearing _before_ the "cut here" line.  This appears to have been a
long-standing bug on architectures that used __WARN_TAINT, but it didn't
get fixed.

v4.11 and earlier on x86:

  ------------[ cut here ]------------
  WARNING: CPU: 0 PID: 2956 at drivers/misc/lkdtm_bugs.c:65 lkdtm_WARNING+0x21/0x30
  This is a warning message
  Modules linked in:

v4.12 and later on x86:

  This is a warning message
  ------------[ cut here ]------------
  WARNING: CPU: 1 PID: 2982 at drivers/misc/lkdtm_bugs.c:68 lkdtm_WARNING+0x15/0x20
  Modules linked in:

With this fix:

  ------------[ cut here ]------------
  This is a warning message
  WARNING: CPU: 3 PID: 3009 at drivers/misc/lkdtm_bugs.c:67 lkdtm_WARNING+0x15/0x20

Since the __FILE__ reporting happens as part of the UD0 handler, it
isn't trivial to move the message to after the WARNING line, but at
least we can fix the position of the "cut here" line so all the various
logging tools will start including the actual runtime warning message
again, when they follow the instruction and "cut here".

Link: http://lkml.kernel.org/r/1510100869-73751-4-git-send-email-keescook@chromium.org


Fixes: 9a93848f ("x86/debug: Implement __WARN() using UD0")
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 2a8358d8

include/asm-generic/bug.h

+3 −2

Original line number	Diff line number	Diff line
		@@ -92,10 +92,11 @@ extern void warn_slowpath_null(const char *file, const int line);
		#define __WARN_printf_taint(taint, arg...) \
		warn_slowpath_fmt_taint(__FILE__, __LINE__, taint, arg)
		#else
		extern __printf(1, 2) void __warn_printk(const char *fmt, ...);
		#define __WARN() __WARN_TAINT(TAINT_WARN)
		#define __WARN_printf(arg...) do { printk(arg); __WARN(); } while (0)
		#define __WARN_printf(arg...) do { __warn_printk(arg); __WARN(); } while (0)
		#define __WARN_printf_taint(taint, arg...) \
		do { printk(arg); __WARN_TAINT(taint); } while (0)
		do { __warn_printk(arg); __WARN_TAINT(taint); } while (0)
		#endif

		/* used internally by panic.c */

kernel/panic.c

+15 −1

Original line number	Diff line number	Diff line
		@@ -520,6 +520,7 @@ void __warn(const char file, int line, void caller, unsigned taint,
		{
		disable_trace_on_warning();

		if (args)
		pr_warn(CUT_HERE);

		if (file)
		@@ -584,9 +585,22 @@ EXPORT_SYMBOL(warn_slowpath_fmt_taint);

		void warn_slowpath_null(const char *file, int line)
		{
		pr_warn(CUT_HERE);
		__warn(file, line, __builtin_return_address(0), TAINT_WARN, NULL, NULL);
		}
		EXPORT_SYMBOL(warn_slowpath_null);
		#else
		void __warn_printk(const char *fmt, ...)
		{
		va_list args;

		pr_warn(CUT_HERE);

		va_start(args, fmt);
		vprintk(fmt, args);
		va_end(args);
		}
		EXPORT_SYMBOL(__warn_printk);
		#endif

		#ifdef CONFIG_BUG

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