[PATCH v6 1/4] panic: Taint kernel if tests are run

David Gow
2022-07-08T04:49:14Z

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

Add a new taint type, TAINT_TEST to signal that a test has been run.
This will be printed as 'N' (originally for kuNit, as every other
sensible letter was taken.)

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

Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: David Gow <davidgow@google.com>
---

This is v6 of the "make tests taint the kernel" patchset. The only
changes since v5 (which is the version in linux-next at time of writing)
are some rather critical fixes to patch 2/4, where the cruicial check
was inverted. (Oops!)

The 'N' character for the taint is even less useful now that it's no
longer short for kuNit, but all the letters in TEST are taken. :-(

No changes since v5:
https://lore.kernel.org/linux-kselftest/20220702040959.3232874-1-davidgow@google.com/

No changes since v4:
https://lore.kernel.org/linux-kselftest/20220701084744.3002019-1-davidgow@google.com/

Changes since v3:
https://lore.kernel.org/lkml/20220513083212.3537869-1-davidgow@google.com/
- Remove the mention of KUnit from the documentation.
- Add Luis and Brendan's Acked/Reviewed-by tags.

Changes since v2:
https://lore.kernel.org/linux-kselftest/20220430030019.803481-1-davidgow@google.com/
- Rename TAINT_KUNIT -> TAINT_TEST.
- Split into separate patches for adding the taint, and triggering it.
- Taint on a kselftest_module being loaded (patch 3/3)

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 +
3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/tainted-kernels.rst b/Documentation/admin-guide/tainted-kernels.rst
index ceeed7b0798d..7d80e8c307d1 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 an in-kernel 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 e71161da69c4..c7759b3f2045 100644
--- a/include/linux/panic.h
+++ b/include/linux/panic.h
@@ -68,7 +68,8 @@ 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_TEST 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 a3c758dba15a..6b3369e21026 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -428,6 +428,7 @@ const struct taint_flag taint_flags[TAINT_FLAGS_COUNT] = {
[ TAINT_LIVEPATCH ] = { 'K', ' ', true },
[ TAINT_AUX ] = { 'X', ' ', true },
[ TAINT_RANDSTRUCT ] = { 'T', ' ', true },
+ [ TAINT_TEST ] = { 'N', ' ', true },
};

/**
--
2.37.0.rc0.161.g10f37bed90-goog