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devices and drivers
The ability to add and remove devices from a driver through the sysfs
"bind" and "unbind" files was created all those decades ago as a way
that kernel developers can iterate faster, and provide a debugging way
for users to attempt to add a new device to a driver without having to
rebuild their kernel.
This api over the years has been abused and recently come under a major
fuzzing "attack" through tools like syzbot which decided that it would
attempt to just randomly bind any driver to any type of device, causing
loads of unneeded errors and pointless kernel patches to be generated by
unsuspecting new developers.
Handle all of this by adding a new taint flag, TAINT_FORCED_BIND, which
will be set on the driver if the bind/unbind sysfs files are ever
written to. This lets kernel developers "know" that a user is
attempting to do something that is not normal, and as such, if the
kernel breaks they get to keep the shiny pieces laying around on the
floor.
The flag is 'Y' which was unused, and can remembered as the user is
"yeeting" the device being operated on here (thrown with force without
regard for the thing being thrown).
Note, the taint flag gets set _BEFORE_ the bind/unbind callback happens,
as many times crashes/oops/warnings/failures happen within the callback,
and the taint flag needs to be there to show what was being attempted.
If it were to be set after the callback happens, the oops report would
not properly reflect what foolishness was being attempted.
Fuzzing tools like syzbot, that doesn't have hand-crafted rules to keep
the tool from hitting bind/unbind, should be run with panic_on_taint
enabled so that they fall over and don't continue on, thinking that they
actually found a real issue.
Userspace operations that rely on the bind/unbind files to work around
the lack of will to upgrade a kernel image to a newer version with
proper support for new devices, or the lack of will to submit valid
device ids to driver authors, will still work properly, but now the
kernel will be flagged in a way that will show that perhaps those users
should reconsider their behavior and work to have the drivers properly
support these devices in a "native" manner.
Finally, the bind/unbind files can find real use-after-free issues with
some drivers by forcing the process to happen virtually without having
to rely on manual removal processes. Those real bugs should still be
worked on, but by adding this taint flag, developers can more easily
determine bug reports that are actually worth looking at.
Reviewed-by: Johan Hovold <johan@kernel.org>
Tested-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Aaron Tomlin <atomlin@atomlin.com>
Reviewed-by: Bradley Morgan <brads@mainlining.org>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patch.msgid.link/20260914-bind_taint-v4-3-eadf8a090903@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Check all loaded modules and report any that have their 'taint'
flags set. The tainted module output format is:
* <module_name> (<taint_flags>)
Example output:
Kernel is "tainted" for the following reasons:
* externally-built ('out-of-tree') module was loaded (#12)
* unsigned module was loaded (#13)
Raw taint value as int/string: 12288/'G OE '
Tainted modules:
* dump_test (OE)
Link: https://lkml.kernel.org/r/20260115064756.531592-1-rdunlap@infradead.org
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Thorsten Leemhuis <linux@leemhuis.info>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Requesting a fwctl scope of access that includes mutating device debug
data will cause the kernel to be tainted. Changing the device operation
through things in the debug scope may cause the device to malfunction in
undefined ways. This should be reflected in the TAINT flags to help any
debuggers understand that something has been done.
Link: https://patch.msgid.link/r/4-v5-642aa0c94070+4447f-fwctl_jgg@nvidia.com
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>
Tested-by: Dave Jiang <dave.jiang@intel.com>
Tested-by: Shannon Nelson <shannon.nelson@amd.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
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Commit c272612cb4a2 ("kunit: Taint the kernel when KUnit tests are run")
added a new taint flag for when in-kernel tests run. This commit adds
recognition of this new flag in kernel-chktaint.
With this change the correct reason will be reported if the kernel is
tainted because of a test run.
Amended Commit log: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Joe Fradley <joefradley@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
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There is a double "the" in a message in kernel-chktaint, fix it.
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210613202059.80403-1-colin.king@canonical.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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This patch fixes a spelling typo in kernel-chktaint
Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20210402070514.336376-1-standby24x7@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Here's a patch updating the meaning of TAINT_CPU_OUT_OF_SPEC after
Borislav introduced changes in a7e1f67ed29f and upcoming patches in tip.
TAINT_CPU_OUT_OF_SPEC now means a bit more what it implies as the
flag isn't set just because of a CPU misconfiguration or mismatch.
Historically it was for SMP kernel oops on an officially SMP incapable
processor but now it also covers CPUs whose MSRs have been incorrectly
poked at from userspace, drivers being used on non supported
architectures, broken firmware, mismatched CPUs, ...
Update documentation and script to reflect that.
Signed-off-by: Mathieu Chouquet-Stringer <me@mathieu.digital>
Link: https://lore.kernel.org/r/20201202153244.709752-1-me@mathieu.digital
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Add a script to the tools/ directory that shows if or why the running
kernel was tainted. The script was mostly written by Randy Dunlap; I
enhanced the script a bit. There does not appear to be a good home for
this script. so create tools/debugging for tools of this nature.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
[ jc: fixed conflicts, rewrote changelog ]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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