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157
Documentation/admin-guide/tainted-kernels.rst
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@ -1,59 +1,164 @@
Tainted kernels
---------------
Some oops reports contain the string **'Tainted: '** after the program
counter. This indicates that the kernel has been tainted by some
mechanism. The string is followed by a series of position-sensitive
characters, each representing a particular tainted value.
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.
1) ``G`` if all modules loaded have a GPL or compatible license, ``P`` if
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 above example it looks like this::
Tainted: P W O
The meaning of those characters is explained in the table below. In tis 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 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 SMP kernel oops on an officially SMP incapable processor
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
=== === ====== ========================================================
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.
2) ``F`` if any module was force loaded by ``insmod -f``, ``' '`` if all
1) ``F`` if any module was force loaded by ``insmod -f``, ``' '`` if all
modules were loaded normally.
3) ``S`` if the oops occurred on an SMP kernel running on hardware that
2) ``S`` if the oops occurred on an SMP kernel running on hardware that
hasn't been certified as safe to run multiprocessor.
Currently this occurs only on various Athlons that are not
SMP capable.
4) ``R`` if a module was force unloaded by ``rmmod -f``, ``' '`` if all
3) ``R`` if a module was force unloaded by ``rmmod -f``, ``' '`` if all
modules were unloaded normally.
5) ``M`` if any processor has reported a Machine Check Exception,
4) ``M`` if any processor has reported a Machine Check Exception,
``' '`` if no Machine Check Exceptions have occurred.
6) ``B`` if a page-release function has found a bad page reference or
some unexpected page flags.
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
occured.
7) ``U`` if a user or user application specifically requested that the
6) ``U`` if a user or user application specifically requested that the
Tainted flag be set, ``' '`` otherwise.
8) ``D`` if the kernel has died recently, i.e. there was an OOPS or BUG.
7) ``D`` if the kernel has died recently, i.e. there was an OOPS or BUG.
9) ``A`` if the ACPI table has been overridden.
8) ``A`` if an ACPI table has been overridden.
10) ``W`` if a warning has previously been issued by the kernel.
9) ``W`` if a warning has previously been issued by the kernel.
(Though some warnings may set more specific taint flags.)
11) ``C`` if a staging driver has been loaded.
10) ``C`` if a staging driver has been loaded.
12) ``I`` if the kernel is working around a severe bug in the platform
11) ``I`` if the kernel is working around a severe bug in the platform
firmware (BIOS or similar).
13) ``O`` if an externally-built ("out-of-tree") module has been loaded.
12) ``O`` if an externally-built ("out-of-tree") module has been loaded.
14) ``E`` if an unsigned module has been loaded in a kernel supporting
13) ``E`` if an unsigned module has been loaded in a kernel supporting
module signature.
15) ``L`` if a soft lockup has previously occurred on the system.
14) ``L`` if a soft lockup has previously occurred on the system.
16) ``K`` if the kernel has been live patched.
15) ``K`` if the kernel has been live patched.
The primary reason for the **'Tainted: '** string is to tell kernel
debuggers if this is a clean kernel or if anything unusual has
occurred. Tainting is permanent: even if an offending module is
unloaded, the tainted value remains to indicate that the kernel is not
trustworthy.
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.

50
Documentation/sysctl/kernel.txt
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@ -94,7 +94,7 @@ show up in /proc/sys/kernel:
- stop-a [ SPARC only ]
- sysrq ==> Documentation/admin-guide/sysrq.rst
- sysctl_writes_strict
- tainted
- tainted ==> Documentation/admin-guide/tainted-kernels.rst
- threads-max
- unknown_nmi_panic
- watchdog
@ -1019,39 +1019,33 @@ compilation sees a 1% slowdown, other systems and workloads may vary.
1: kernel stack erasing is enabled (default), it is performed before
returning to the userspace at the end of syscalls.
==============================================================
tainted:
tainted
Non-zero if the kernel has been tainted. Numeric values, which can be
ORed together. The letters are seen in "Tainted" line of Oops reports.
1 (P): A module with a non-GPL license has been loaded, this
includes modules with no license.
Set by modutils >= 2.4.9 and module-init-tools.
2 (F): A module was force loaded by insmod -f.
Set by modutils >= 2.4.9 and module-init-tools.
4 (S): Unsafe SMP processors: SMP with CPUs not designed for SMP.
8 (R): A module was forcibly unloaded from the system by rmmod -f.
16 (M): A hardware machine check error occurred on the system.
32 (B): A bad page was discovered on the system.
64 (U): The user has asked that the system be marked "tainted". This
could be because they are running software that directly modifies
the hardware, or for other reasons.
128 (D): The system has died.
256 (A): The ACPI DSDT has been overridden with one supplied by the user
instead of using the one provided by the hardware.
512 (W): A kernel warning has occurred.
1024 (C): A module from drivers/staging was loaded.
2048 (I): The system is working around a severe firmware bug.
4096 (O): An out-of-tree module has been loaded.
8192 (E): An unsigned module has been loaded in a kernel supporting module
signature.
16384 (L): A soft lockup has previously occurred on the system.
32768 (K): The 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.
1 (P): proprietary module was loaded
2 (F): module was force loaded
4 (S): SMP kernel oops on an officially SMP incapable processor
8 (R): module was force unloaded
16 (M): processor reported a Machine Check Exception (MCE)
32 (B): bad page referenced or some unexpected page flags
64 (U): taint requested by userspace application
128 (D): kernel died recently, i.e. there was an OOPS or BUG
256 (A): an ACPI table was overridden by user
512 (W): kernel issued warning
1024 (C): staging driver was loaded
2048 (I): workaround for bug in platform firmware applied
4096 (O): externally-built ("out-of-tree") module was loaded
8192 (E): unsigned module was loaded
16384 (L): soft lockup occurred
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
See Documentation/admin-guide/tainted-kernels.rst for more information.
==============================================================

14
tools/Makefile
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@ -12,6 +12,7 @@ help:
@echo ' acpi - ACPI tools'
@echo ' cgroup - cgroup tools'
@echo ' cpupower - a tool for all things x86 CPU power'
@echo ' debugging - tools for debugging'
@echo ' firewire - the userspace part of nosy, an IEEE-1394 traffic sniffer'
@echo ' firmware - Firmware tools'
@echo ' freefall - laptop accelerometer program for disk protection'
@ -61,7 +62,7 @@ acpi: FORCE
cpupower: FORCE
$(call descend,power/$@)
cgroup firewire hv guest spi usb virtio vm bpf iio gpio objtool leds wmi pci firmware: FORCE
cgroup firewire hv guest spi usb virtio vm bpf iio gpio objtool leds wmi pci firmware debugging: FORCE
$(call descend,$@)
liblockdep: FORCE
@ -96,7 +97,8 @@ kvm_stat: FORCE
all: acpi cgroup cpupower gpio hv firewire liblockdep \
perf selftests spi turbostat usb \
virtio vm bpf x86_energy_perf_policy \
tmon freefall iio objtool kvm_stat wmi pci
tmon freefall iio objtool kvm_stat wmi \
pci debugging
acpi_install:
$(call descend,power/$(@:_install=),install)
@ -104,7 +106,7 @@ acpi_install:
cpupower_install:
$(call descend,power/$(@:_install=),install)
cgroup_install firewire_install gpio_install hv_install iio_install perf_install spi_install usb_install virtio_install vm_install bpf_install objtool_install wmi_install pci_install:
cgroup_install firewire_install gpio_install hv_install iio_install perf_install spi_install usb_install virtio_install vm_install bpf_install objtool_install wmi_install pci_install debugging_install:
$(call descend,$(@:_install=),install)
liblockdep_install:
@ -130,7 +132,7 @@ install: acpi_install cgroup_install cpupower_install gpio_install \
perf_install selftests_install turbostat_install usb_install \
virtio_install vm_install bpf_install x86_energy_perf_policy_install \
tmon_install freefall_install objtool_install kvm_stat_install \
wmi_install pci_install
wmi_install pci_install debugging_install
acpi_clean:
$(call descend,power/acpi,clean)
@ -138,7 +140,7 @@ acpi_clean:
cpupower_clean:
$(call descend,power/cpupower,clean)
cgroup_clean hv_clean firewire_clean spi_clean usb_clean virtio_clean vm_clean wmi_clean bpf_clean iio_clean gpio_clean objtool_clean leds_clean pci_clean firmware_clean:
cgroup_clean hv_clean firewire_clean spi_clean usb_clean virtio_clean vm_clean wmi_clean bpf_clean iio_clean gpio_clean objtool_clean leds_clean pci_clean firmware_clean debugging_clean:
$(call descend,$(@:_clean=),clean)
liblockdep_clean:
@ -176,6 +178,6 @@ clean: acpi_clean cgroup_clean cpupower_clean hv_clean firewire_clean \
perf_clean selftests_clean turbostat_clean spi_clean usb_clean virtio_clean \
vm_clean bpf_clean iio_clean x86_energy_perf_policy_clean tmon_clean \
freefall_clean build_clean libbpf_clean libsubcmd_clean liblockdep_clean \
gpio_clean objtool_clean leds_clean wmi_clean pci_clean firmware_clean
gpio_clean objtool_clean leds_clean wmi_clean pci_clean firmware_clean debugging_clean
.PHONY: FORCE

16
tools/debugging/Makefile Normal file
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@ -0,0 +1,16 @@
# SPDX-License-Identifier: GPL-2.0
# Makefile for debugging tools
PREFIX ?= /usr
BINDIR ?= bin
INSTALL ?= install
TARGET = kernel-chktaint
all: $(TARGET)
clean:
install: kernel-chktaint
$(INSTALL) -D -m 755 $(TARGET) $(DESTDIR)$(PREFIX)/$(BINDIR)/$(TARGET)

202
tools/debugging/kernel-chktaint Executable file
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@ -0,0 +1,202 @@
#! /bin/sh
# SPDX-License-Identifier: GPL-2.0
#
# Randy Dunlap <rdunlap@infradead.org>, 2018
# Thorsten Leemhuis <linux@leemhuis.info>, 2018
usage()
{
cat <<EOF
usage: ${0##*/}
${0##*/} <int>
Call without parameters to decode /proc/sys/kernel/tainted.
Call with a positive integer as parameter to decode a value you
retrieved from /proc/sys/kernel/tainted on another system.
EOF
}
if [ "$1"x != "x" ]; then
if [ "$1"x == "--helpx" ] || [ "$1"x == "-hx" ] ; then
usage
exit 1
elif [ $1 -ge 0 ] 2>/dev/null ; then
taint=$1
else
echo "Error: Parameter '$1' not a positive interger. Aborting." >&2
exit 1
fi
else
TAINTFILE="/proc/sys/kernel/tainted"
if [ ! -r $TAINTFILE ]; then
echo "No file: $TAINTFILE"
exit
fi
taint=`cat $TAINTFILE`
fi
if [ $taint -eq 0 ]; then
echo "Kernel not Tainted"
exit
else
echo "Kernel is \"tainted\" for the following reasons:"
fi
T=$taint
out=
addout() {
out=$out$1
}
if [ `expr $T % 2` -eq 0 ]; then
addout "G"
else
addout "P"
echo " * proprietary module was loaded (#0)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "F"
echo " * module was force loaded (#1)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "S"
echo " * SMP kernel oops on an officially SMP incapable processor (#2)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "R"
echo " * module was force unloaded (#3)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "M"
echo " * processor reported a Machine Check Exception (MCE) (#4)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "B"
echo " * bad page referenced or some unexpected page flags (#5)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "U"
echo " * taint requested by userspace application (#6)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "D"
echo " * kernel died recently, i.e. there was an OOPS or BUG (#7)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "A"
echo " * an ACPI table was overridden by user (#8)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "W"
echo " * kernel issued warning (#9)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "C"
echo " * staging driver was loaded (#10)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "I"
echo " * workaround for bug in platform firmware applied (#11)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "O"
echo " * externally-built ('out-of-tree') module was loaded (#12)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "E"
echo " * unsigned module was loaded (#13)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "L"
echo " * soft lockup occurred (#14)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "K"
echo " * kernel has been live patched (#15)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "X"
echo " * auxiliary taint, defined for and used by distros (#16)"
fi
T=`expr $T / 2`
if [ `expr $T % 2` -eq 0 ]; then
addout " "
else
addout "T"
echo " * kernel was built with the struct randomization plugin (#17)"
fi
echo "For a more detailed explanation of the various taint flags see"
echo " Documentation/admin-guide/tainted-kernels.rst in the the Linux kernel sources"
echo " or https://kernel.org/doc/html/latest/admin-guide/tainted-kernels.html"
echo "Raw taint value as int/string: $taint/'$out'"
#EOF#