On Wed, Mar 16, 2022 at 01:48:49PM +0000, Limonciello, Mario wrote: > [Public] > > > > > IOMMU is active > > > > > > > > Hi Mario, > > > > > > > > On Tue, Mar 15, 2022 at 04:30:08PM -0500, Mario Limonciello wrote: > > > > > Historically TBT3 in Linux used "Thunderbolt security levels" as a primary > > > > > means of "security" against DMA attacks. This mean that users would > > need > > > > to > > > > > ack any device plugged in via userspace. In ~2018 machines started to > > use > > > > > the IOMMU for protection, but instead of dropping security levels a > > > > > convoluted flow was introduced: > > > > > * User hotplugs device > > > > > * Driver discovers supported tunnels > > > > > * Driver emits a uevent to userspace that a PCIe tunnel is present > > > > > * Userspace reads 'iommu_dma_protection' attribute (which currently > > > > > indicates an Intel IOMMU is present and was enabled pre-boot not > > that > > > > > it's active "now") > > > > > * Based on that value userspace then authorizes automatically or > > prompts > > > > > the user like how security level based support worked. > > > > > > > > There are legitimate reasons to disable PCIe tunneling even if the > > IOMMU > > > > bits are in place. The ACPI _OSC allows the boot firmware to do so and > > > > our "security levels" allows the userspace policy to do the same. I > > > > would not like to change that unless absolutely necessary. > > > > > > Actually I intentionally left that in the RFC patch, to only do this based off > > > of tb_acpi_may_tunnel_pcie, so I think that should still work as you > > described > > > if boot firmware turned off PCIe tunneling. > > > > Right but if the user still wants to disable it, like say you are > > travelling and you want to be sure that no PCIe devices get attached > > while your laptop is charging from a public "charging station" (whatever > > is the right term). > > So wouldn't you flip the default in BIOS setup to disable PCIe tunnels then for > this use case? What if you are on Chromebook? Or something where this is not user configurable? > Otherwise with how it is today you end up with the PCIe tunnel created in the > boot FW and then coming into the OS if it's the same path the tunnel stays > in place with no opportunity for userspace to authorize it, no? The boot FW does not need to support CM capabilites nor does it need to provide the ACPI _OSC.
