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| -rw-r--r-- | Documentation/admin-guide/thunderbolt.rst | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/Documentation/admin-guide/thunderbolt.rst b/Documentation/admin-guide/thunderbolt.rst index 613cb24c76c7..f18e881373c4 100644 --- a/Documentation/admin-guide/thunderbolt.rst +++ b/Documentation/admin-guide/thunderbolt.rst @@ -47,6 +47,9 @@ be DMA masters and thus read contents of the host memory without CPU and OS knowing about it. There are ways to prevent this by setting up an IOMMU but it is not always available for various reasons. +Some USB4 systems have a BIOS setting to disable PCIe tunneling. This is +treated as another security level (nopcie). + The security levels are as follows: none @@ -77,6 +80,10 @@ The security levels are as follows: Display Port in a dock. All PCIe links downstream of the dock are removed. + nopcie + PCIe tunneling is disabled/forbidden from the BIOS. Available in some + USB4 systems. + The current security level can be read from ``/sys/bus/thunderbolt/devices/domainX/security`` where ``domainX`` is the Thunderbolt domain the host controller manages. There is typically @@ -153,6 +160,22 @@ If the user still wants to connect the device they can either approve the device without a key or write a new key and write 1 to the ``authorized`` file to get the new key stored on the device NVM. +De-authorizing devices +---------------------- +It is possible to de-authorize devices by writing ``0`` to their +``authorized`` attribute. This requires support from the connection +manager implementation and can be checked by reading domain +``deauthorization`` attribute. If it reads ``1`` then the feature is +supported. + +When a device is de-authorized the PCIe tunnel from the parent device +PCIe downstream (or root) port to the device PCIe upstream port is torn +down. This is essentially the same thing as PCIe hot-remove and the PCIe +toplogy in question will not be accessible anymore until the device is +authorized again. If there is storage such as NVMe or similar involved, +there is a risk for data loss if the filesystem on that storage is not +properly shut down. You have been warned! + DMA protection utilizing IOMMU ------------------------------ Recent systems from 2018 and forward with Thunderbolt ports may natively |