On Thu, Aug 1, 2019 at 10:40 AM Sumit Garg sumit.garg@linaro.org wrote:
I chose the userspace plugin due to this, you can use userspace aids to provide any type of service. Use the crypto library you desire to do the magic you want.
Here TEE isn't similar to a user-space crypto library. In our case TEE is based on ARM TrustZone which only allows TEE communications to be initiated from privileged mode. So why would you like to route communications via user-mode (which is less secure) when we have standardised TEE interface available in kernel?
The physical access guards for reading/writing the involved critical memory are identical as far as I know? Layered security is generally a good thing, and the userspace pass actually adds a layer, so not sure which is really safer?
In my case the rerouting was to done generalize it. Any type of trust source, anywhere.
Isn't actual purpose to have trusted keys is to protect user-space from access to kernel keys in plain format? Doesn't user mode helper defeat that purpose in one way or another?
Not really. CPU is in the user mode while running the code, but the code or the secure keydata being is not available to the 'normal' userspace. It's like microkernel service/driver this way. The usermode driver is part of the kernel image and it runs on top of a invisible rootfs.
Can you elaborate here with an example regarding how this user-mode helper will securely communicate with a hardware based trust source with other user-space processes denied access to that trust source?
The other user mode processes will never see the device node to open. There is none in existence for them; it only exists in the ramfs based root for the user mode helper.
-- Janne