[PATCH v2] kunit: Taint kernel if any tests run

[David Gow <davidgow@google.com>]

KUnit tests are not supposed to run on production systems: they may do
deliberately illegal things to trigger errors, and have security
implications (assertions will often deliberately leak kernel addresses).

Add a new taint type, TAINT_KUNIT to signal that a KUnit test has been
run. This will be printed as 'N' (for kuNit, as K, U and T were already
taken).

This should discourage people from running KUnit tests on production
systems, and to make it easier to tell if tests have been run
accidentally (by loading the wrong configuration, etc.)

Signed-off-by: David Gow <davidgow@google.com>
---

Changes since v1:
https://lore.kernel.org/linux-kselftest/20220429043913.626647-1-davidgow@google.com/
- Make the taint per-module, to handle the case when tests are in
  (longer lasting) modules. (Thanks Greg KH).

Note that this still has checkpatch.pl warnings around bracket
placement, which are intentional as part of matching the surrounding
code.

---
 Documentation/admin-guide/tainted-kernels.rst | 1 +
 include/linux/panic.h                         | 3 ++-
 kernel/panic.c                                | 1 +
 lib/kunit/test.c                              | 4 ++++
 4 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/tainted-kernels.rst b/Documentation/admin-guide/tainted-kernels.rst
index ceeed7b0798d..8f18fc4659d4 100644
--- a/Documentation/admin-guide/tainted-kernels.rst
+++ b/Documentation/admin-guide/tainted-kernels.rst
@@ -100,6 +100,7 @@ Bit  Log  Number  Reason that got the kernel tainted
  15  _/K   32768  kernel has been live patched
  16  _/X   65536  auxiliary taint, defined for and used by distros
  17  _/T  131072  kernel was built with the struct randomization plugin
+ 18  _/N  262144  a KUnit test has been run
 ===  ===  ======  ========================================================
 
 Note: The character ``_`` is representing a blank in this table to make reading
diff --git a/include/linux/panic.h b/include/linux/panic.h
index f5844908a089..1d316c26bf27 100644
--- a/include/linux/panic.h
+++ b/include/linux/panic.h
@@ -74,7 +74,8 @@ static inline void set_arch_panic_timeout(int timeout, int arch_default_timeout)
 #define TAINT_LIVEPATCH			15
 #define TAINT_AUX			16
 #define TAINT_RANDSTRUCT		17
-#define TAINT_FLAGS_COUNT		18
+#define TAINT_KUNIT			18
+#define TAINT_FLAGS_COUNT		19
 #define TAINT_FLAGS_MAX			((1UL << TAINT_FLAGS_COUNT) - 1)
 
 struct taint_flag {
diff --git a/kernel/panic.c b/kernel/panic.c
index eb4dfb932c85..9a026d98a00c 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -404,6 +404,7 @@ const struct taint_flag taint_flags[TAINT_FLAGS_COUNT] = {
 	[ TAINT_LIVEPATCH ]		= { 'K', ' ', true },
 	[ TAINT_AUX ]			= { 'X', ' ', true },
 	[ TAINT_RANDSTRUCT ]		= { 'T', ' ', true },
+	[ TAINT_KUNIT ]			= { 'N', ' ', true },
 };
 
 /**
diff --git a/lib/kunit/test.c b/lib/kunit/test.c
index 0f66c13d126e..ea8e9162445d 100644
--- a/lib/kunit/test.c
+++ b/lib/kunit/test.c
@@ -11,6 +11,7 @@
 #include <kunit/test-bug.h>
 #include <linux/kernel.h>
 #include <linux/moduleparam.h>
+#include <linux/panic.h>
 #include <linux/sched/debug.h>
 #include <linux/sched.h>
 
@@ -498,6 +499,9 @@ int kunit_run_tests(struct kunit_suite *suite)
 	struct kunit_result_stats suite_stats = { 0 };
 	struct kunit_result_stats total_stats = { 0 };
 
+	/* Taint the kernel so we know we've run tests. */
+	add_taint(TAINT_KUNIT, LOCKDEP_STILL_OK);
+
 	kunit_print_subtest_start(suite);
 
 	kunit_suite_for_each_test_case(suite, test_case) {
-- 
2.36.0.464.gb9c8b46e94-goog