185 lines
8.8 KiB
ReStructuredText
185 lines
8.8 KiB
ReStructuredText
Tainted kernels
|
|
---------------
|
|
|
|
The kernel will mark itself as 'tainted' when something occurs that might be
|
|
relevant later when investigating problems. Don't worry too much about this,
|
|
most of the time it's not a problem to run a tainted kernel; the information is
|
|
mainly of interest once someone wants to investigate some problem, as its real
|
|
cause might be the event that got the kernel tainted. That's why bug reports
|
|
from tainted kernels will often be ignored by developers, hence try to reproduce
|
|
problems with an untainted kernel.
|
|
|
|
Note the kernel will remain tainted even after you undo what caused the taint
|
|
(i.e. unload a proprietary kernel module), to indicate the kernel remains not
|
|
trustworthy. That's also why the kernel will print the tainted state when it
|
|
notices an internal problem (a 'kernel bug'), a recoverable error
|
|
('kernel oops') or a non-recoverable error ('kernel panic') and writes debug
|
|
information about this to the logs ``dmesg`` outputs. It's also possible to
|
|
check the tainted state at runtime through a file in ``/proc/``.
|
|
|
|
|
|
Tainted flag in bugs, oops or panics messages
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
You find the tainted state near the top in a line starting with 'CPU:'; if or
|
|
why the kernel was tainted is shown after the Process ID ('PID:') and a shortened
|
|
name of the command ('Comm:') that triggered the event::
|
|
|
|
BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
|
|
Oops: 0002 [#1] SMP PTI
|
|
CPU: 0 PID: 4424 Comm: insmod Tainted: P W O 4.20.0-0.rc6.fc30 #1
|
|
Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
|
|
RIP: 0010:my_oops_init+0x13/0x1000 [kpanic]
|
|
[...]
|
|
|
|
You'll find a 'Not tainted: ' there if the kernel was not tainted at the
|
|
time of the event; if it was, then it will print 'Tainted: ' and characters
|
|
either letters or blanks. In the example above it looks like this::
|
|
|
|
Tainted: P W O
|
|
|
|
The meaning of those characters is explained in the table below. In this case
|
|
the kernel got tainted earlier because a proprietary Module (``P``) was loaded,
|
|
a warning occurred (``W``), and an externally-built module was loaded (``O``).
|
|
To decode other letters use the table below.
|
|
|
|
|
|
Decoding tainted state at runtime
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
At runtime, you can query the tainted state by reading
|
|
``cat /proc/sys/kernel/tainted``. If that returns ``0``, the kernel is not
|
|
tainted; any other number indicates the reasons why it is. The easiest way to
|
|
decode that number is the script ``tools/debugging/kernel-chktaint``, which your
|
|
distribution might ship as part of a package called ``linux-tools`` or
|
|
``kernel-tools``; if it doesn't, you can download the script from
|
|
`git.kernel.org <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/tools/debugging/kernel-chktaint>`_
|
|
and execute it with ``sh kernel-chktaint``, which would print something like
|
|
this on the machine that had the statements in the logs that were quoted earlier::
|
|
|
|
Kernel is Tainted for following reasons:
|
|
* Proprietary module was loaded (#0)
|
|
* Kernel issued warning (#9)
|
|
* Externally-built ('out-of-tree') module was loaded (#12)
|
|
See Documentation/admin-guide/tainted-kernels.rst in the Linux kernel or
|
|
https://www.kernel.org/doc/html/latest/admin-guide/tainted-kernels.html for
|
|
a more details explanation of the various taint flags.
|
|
Raw taint value as int/string: 4609/'P W O '
|
|
|
|
You can try to decode the number yourself. That's easy if there was only one
|
|
reason that got your kernel tainted, as in this case you can find the number
|
|
with the table below. If there were multiple reasons you need to decode the
|
|
number, as it is a bitfield, where each bit indicates the absence or presence of
|
|
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
|
|
|
|
Table for decoding tainted state
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
=== === ====== ========================================================
|
|
Bit Log Number Reason that got the kernel tainted
|
|
=== === ====== ========================================================
|
|
0 G/P 1 proprietary module was loaded
|
|
1 _/F 2 module was force loaded
|
|
2 _/S 4 kernel running on an out of specification system
|
|
3 _/R 8 module was force unloaded
|
|
4 _/M 16 processor reported a Machine Check Exception (MCE)
|
|
5 _/B 32 bad page referenced or some unexpected page flags
|
|
6 _/U 64 taint requested by userspace application
|
|
7 _/D 128 kernel died recently, i.e. there was an OOPS or BUG
|
|
8 _/A 256 ACPI table overridden by user
|
|
9 _/W 512 kernel issued warning
|
|
10 _/C 1024 staging driver was loaded
|
|
11 _/I 2048 workaround for bug in platform firmware applied
|
|
12 _/O 4096 externally-built ("out-of-tree") module was loaded
|
|
13 _/E 8192 unsigned module was loaded
|
|
14 _/L 16384 soft lockup occurred
|
|
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
|
|
easier.
|
|
|
|
More detailed explanation for tainting
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
0) ``G`` if all modules loaded have a GPL or compatible license, ``P`` if
|
|
any proprietary module has been loaded. Modules without a
|
|
MODULE_LICENSE or with a MODULE_LICENSE that is not recognised by
|
|
insmod as GPL compatible are assumed to be proprietary.
|
|
|
|
1) ``F`` if any module was force loaded by ``insmod -f``, ``' '`` if all
|
|
modules were loaded normally.
|
|
|
|
2) ``S`` if the kernel is running on a processor or system that is out of
|
|
specification: hardware has been put into an unsupported configuration,
|
|
therefore proper execution cannot be guaranteed.
|
|
Kernel will be tainted if, for example:
|
|
|
|
- on x86: PAE is forced through forcepae on intel CPUs (such as Pentium M)
|
|
which do not report PAE but may have a functional implementation, an SMP
|
|
kernel is running on non officially capable SMP Athlon CPUs, MSRs are
|
|
being poked at from userspace.
|
|
- on arm: kernel running on certain CPUs (such as Keystone 2) without
|
|
having certain kernel features enabled.
|
|
- on arm64: there are mismatched hardware features between CPUs, the
|
|
bootloader has booted CPUs in different modes.
|
|
- certain drivers are being used on non supported architectures (such as
|
|
scsi/snic on something else than x86_64, scsi/ips on non
|
|
x86/x86_64/itanium, have broken firmware settings for the
|
|
irqchip/irq-gic on arm64 ...).
|
|
- x86/x86_64: Microcode late loading is dangerous and will result in
|
|
tainting the kernel. It requires that all CPUs rendezvous to make sure
|
|
the update happens when the system is as quiescent as possible. However,
|
|
a higher priority MCE/SMI/NMI can move control flow away from that
|
|
rendezvous and interrupt the update, which can be detrimental to the
|
|
machine.
|
|
|
|
3) ``R`` if a module was force unloaded by ``rmmod -f``, ``' '`` if all
|
|
modules were unloaded normally.
|
|
|
|
4) ``M`` if any processor has reported a Machine Check Exception,
|
|
``' '`` if no Machine Check Exceptions have occurred.
|
|
|
|
5) ``B`` If a page-release function has found a bad page reference or some
|
|
unexpected page flags. This indicates a hardware problem or a kernel bug;
|
|
there should be other information in the log indicating why this tainting
|
|
occurred.
|
|
|
|
6) ``U`` if a user or user application specifically requested that the
|
|
Tainted flag be set, ``' '`` otherwise.
|
|
|
|
7) ``D`` if the kernel has died recently, i.e. there was an OOPS or BUG.
|
|
|
|
8) ``A`` if an ACPI table has been overridden.
|
|
|
|
9) ``W`` if a warning has previously been issued by the kernel.
|
|
(Though some warnings may set more specific taint flags.)
|
|
|
|
10) ``C`` if a staging driver has been loaded.
|
|
|
|
11) ``I`` if the kernel is working around a severe bug in the platform
|
|
firmware (BIOS or similar).
|
|
|
|
12) ``O`` if an externally-built ("out-of-tree") module has been loaded.
|
|
|
|
13) ``E`` if an unsigned module has been loaded in a kernel supporting
|
|
module signature.
|
|
|
|
14) ``L`` if a soft lockup has previously occurred on the system.
|
|
|
|
15) ``K`` if the kernel has been live patched.
|
|
|
|
16) ``X`` Auxiliary taint, defined for and used by Linux distributors.
|
|
|
|
17) ``T`` Kernel was build with the randstruct plugin, which can intentionally
|
|
produce extremely unusual kernel structure layouts (even performance
|
|
pathological ones), which is important to know when debugging. Set at
|
|
build time.
|