On Tue, 2 Jun 2020 at 20:14, James Bottomley jejb@linux.ibm.com wrote:
On Tue, 2020-06-02 at 19:48 +0530, Sumit Garg wrote:
Add support for TEE based trusted keys where TEE provides the functionality to seal and unseal trusted keys using hardware unique key. Also, this is an alternative in case platform doesn't possess a TPM device.
So here's a meta problem: in the case when the platform possesses both TEE and TPM what should it do?
IMO, trust source (either a TPM or a TEE) should be unique and carefully chosen as per platform security policy corresponding to a particular threat model.
And moreover TEEs have been mostly used in the embedded world where having a hardware TPM is cumbersome given constraints regarding BoM cost and hardware resources.
Things like this:
--- a/security/keys/trusted-keys/trusted_core.c +++ b/security/keys/trusted-keys/trusted_core.c @@ -25,6 +25,8 @@
#if defined(CONFIG_TRUSTED_TPM) static struct trusted_key_ops *trusted_key_ops = &tpm_trusted_key_ops; +#elif defined(CONFIG_TRUSTED_TEE) +static struct trusted_key_ops *trusted_key_ops = &tee_trusted_key_ops; #else
Say it's either/or at a Kconfig level: so if you select both TEE and TPM based trusted keys at compile time, we intall the TPM ops and ignore the TEE ops, is that right? Surely this should be runtime selectable based on what the platform has ...
This dynamic selection was already part of v4 patch-set but after objection from Jarrko here [1], I switched to compile time mode instead.
[1] https://lkml.org/lkml/2020/6/2/139
perhaps it should even be selectable per key?
Once it is runtime selectable, what should be selected in the both case? Or should we allow the user to decide, if so, how?
when you pipe a trusted key, I think the subtype (TEE or TPM) should be part of the piped information, so it loads again seamlessly. This would actually be fixed by something like the ASN.1 scheme I'm trying to upstream, at least for TPM keys, but do TEE keys have a recognized ASN.1 format?
I guess this is something which we can refine later if there are real platforms that have a particular security requirement to support both TPM and a TEE.
-Sumit
James