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254ef9541d
To avoid the following types of error messages due to a failure by the TPM driver to use the TPM, suspend TPM PCR extensions and the appending of entries to the IMA log once IMA's reboot notifier has been called. This avoids trying to use the TPM after the TPM subsystem has been shut down. [111707.685315][ T1] ima: Error Communicating to TPM chip, result: -19 [111707.685960][ T1] ima: Error Communicating to TPM chip, result: -19 Synchronization with the ima_extend_list_mutex to set ima_measurements_suspended ensures that the TPM subsystem is not shut down when IMA holds the mutex while appending to the log and extending the PCR. The alternative of reading the system_state variable would not provide this guarantee. This error could be observed on a ppc64 machine running SuSE Linux where processes are still accessing files after devices have been shut down. Suspending the IMA log and PCR extensions shortly before reboot does not seem to open a significant measurement gap since neither TPM quoting would work for attestation nor that new log entries could be written to anywhere after devices have been shut down. However, there's a time window between the invocation of the reboot notifier and the shutdown of devices. This includes all subsequently invoked reboot notifiers as well as kernel_restart_prepare() where __usermodehelper_disable() waits for all running_helpers to exit. During this time window IMA could now miss log entries even though attestation would still work. The reboot of the system shortly after may make this small gap insignificant. Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org> Signed-off-by: Mimi Zohar <zohar@linux.ibm.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.