[PATCH 08/14] taint: add taint for direct hardware access

Ben Widawsky
2021-01-30T10:20:34Z

For drivers that moderate access to the underlying hardware it is
sometimes desirable to allow userspace to bypass restrictions. Once
userspace has done this, the driver can no longer guarantee the sanctity
of either the OS or the hardware. When in this state, it is helpful for
kernel developers to be made aware (via this taint flag) of this fact
for subsequent bug reports.

Example usage:
- Hardware xyzzy accepts 2 commands, waldo and fred.
- The xyzzy driver provides an interface for using waldo, but not fred.
- quux is convinced they really need the fred command.
- xyzzy driver allows quux to frob hardware to initiate fred.
- kernel gets tainted.
- turns out fred command is borked, and scribbles over memory.
- developers laugh while closing quux's subsequent bug report.

Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
---
Documentation/admin-guide/sysctl/kernel.rst | 1 +
Documentation/admin-guide/tainted-kernels.rst | 6 +++++-
include/linux/kernel.h | 3 ++-
kernel/panic.c | 1 +
4 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 1d56a6b73a4e..3e1eada53504 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -1352,6 +1352,7 @@ ORed together. The letters are seen in "Tainted" line of Oops reports.
32768 `(K)` kernel has been live patched
65536 `(X)` Auxiliary taint, defined and used by for distros
131072 `(T)` The kernel was built with the struct randomization plugin
+262144 `(H)` The kernel has allowed vendor shenanigans
====== ===== ==============================================================

See :doc:`/admin-guide/tainted-kernels` for more information.
diff --git a/Documentation/admin-guide/tainted-kernels.rst b/Documentation/admin-guide/tainted-kernels.rst
index ceeed7b0798d..ee2913316344 100644
--- a/Documentation/admin-guide/tainted-kernels.rst
+++ b/Documentation/admin-guide/tainted-kernels.rst
@@ -74,7 +74,7 @@ a particular type of taint. It's best to leave that to the aforementioned
script, but if you need something quick you can use this shell command to check
which bits are set::

- $ for i in $(seq 18); do echo $(($i-1)) $(($(cat /proc/sys/kernel/tainted)>>($i-1)&1));done
+ $ for i in $(seq 19); do echo $(($i-1)) $(($(cat /proc/sys/kernel/tainted)>>($i-1)&1));done

Table for decoding tainted state
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -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 _/H 262144 kernel has allowed vendor shenanigans
=== === ====== ========================================================

Note: The character ``_`` is representing a blank in this table to make reading
@@ -175,3 +176,6 @@ More detailed explanation for tainting
produce extremely unusual kernel structure layouts (even performance
pathological ones), which is important to know when debugging. Set at
build time.
+
+ 18) ``H`` Kernel has allowed direct access to hardware and can no longer make
+ any guarantees about the stability of the device or driver.
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index f7902d8c1048..bc95486f817e 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -443,7 +443,8 @@ extern enum system_states {
#define TAINT_LIVEPATCH 15
#define TAINT_AUX 16
#define TAINT_RANDSTRUCT 17
-#define TAINT_FLAGS_COUNT 18
+#define TAINT_RAW_PASSTHROUGH 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 332736a72a58..dff22bd80eaf 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -386,6 +386,7 @@ const struct taint_flag taint_flags[TAINT_FLAGS_COUNT] = {
[ TAINT_LIVEPATCH ] = { 'K', ' ', true },
[ TAINT_AUX ] = { 'X', ' ', true },
[ TAINT_RANDSTRUCT ] = { 'T', ' ', true },
+ [ TAINT_RAW_PASSTHROUGH ] = { 'H', ' ', true },
};

/**
--
2.30.0