c037b6c818
A PCI device is "external_facing" if it's a Root Port with the ACPI "ExternalFacingPort" property or if it has the DT "external-facing" property. We consider everything downstream from such a device to be removable by user. We're mainly concerned with consumer platforms with user accessible Thunderbolt ports that are vulnerable to DMA attacks, and we expect those ports to be identified by firmware as "ExternalFacingPort". Devices in traditional hotplug slots can technically be removed, but the expectation is that unless the port is marked with "ExternalFacingPort", such devices are less accessible to user / may not be removed by end user, and thus not exposed as "removable" to userspace. This can be used to implement userspace policies tailored for user removable devices. Eg usage: https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2591812 https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2795038 (code uses such an attribute to remove external PCI devices or disable features on them as needed by the policy desired) Acked-by: Bjorn Helgaas <bhelgaas@google.com> Signed-off-by: Rajat Jain <rajatja@google.com> Link: https://lore.kernel.org/r/20210524171812.18095-2-rajatja@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
19 lines
797 B
Plaintext
19 lines
797 B
Plaintext
What: /sys/devices/.../removable
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Date: May 2021
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Contact: Rajat Jain <rajatxjain@gmail.com>
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Description:
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Information about whether a given device can be removed from the
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platform by the user. This is determined by its subsystem in a
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bus / platform-specific way. This attribute is only present for
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devices that can support determining such information:
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"removable": device can be removed from the platform by the user
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"fixed": device is fixed to the platform / cannot be removed
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by the user.
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"unknown": The information is unavailable / cannot be deduced.
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Currently this is only supported by USB (which infers the
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information from a combination of hub descriptor bits and
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platform-specific data such as ACPI) and PCI (which gets this
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from ACPI / device tree).
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