On Thu, Jul 26, 2018 at 02:12:04PM +0530, Sumit Garg wrote:
> On Thu, 26 Jul 2018 at 13:20, Daniel Thompson <[email protected]>
> wrote:
> > I guess it could implement a secure monitor call to provide it. In
> > fact I find it a rather pleasing approach. However I think it still loops
> > us round to pretty much the same question as before. Does TF-A "protec
> > " a normal world that makes an SMC to an OP-TEE that isn't there by
> > failing the call in a nice way?
>
> TF-A returns SMC call for OP-TEE as unknown (error code: -1 in "x0"
> register) if OP-TEE is not present.
Be careful here; you can't use an arbitrary SMC since that could be
implemented by another trusted OS (with a completely different meaning).
Assuming you know the system provides SMCCC, you can use the "Call UID
Query" in the trusted OS range, and check that returned value matches
OP-TEE's UID.
i.e
uid = smccc_uid_query(OPTEE_RANGE);
if (uid == OPTEEE_SMCCC_UID) {
[ OP-TEE present ]
} else {
[ unknown/no trusted OS present ]
}
Thanks,
Mark.
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