Vulnerability Advisory : OP-TEE vulnerable to ECDH private key recovery with HIGH Attack Complexity

OP-TEE is a Trusted Execution Environment (TEE) designed as companion to a non-secure Linux kernel running on Arm; Cortex-A cores using the TrustZone technology. Prior to version 4.11.0, on many of the ECDH shared secret paths, the public key isn't verified to be a point on the correct curve. By passing approximately 30-40 crafted public keys to OP-TEE, the private key can be reconstructed by a normal world attacker. When calling TEE_DeriveKey the public key is provided with full X and Y values, but the (X, Y) point might not satisfy the `Y^2 == X^3 + aX + b mod P` math for the specific curve that is used. When those public keys aren't rejected, the attacker can select public keys such that each DeriveKey call will leak `d % r` where `d` is the private key and `r` comes from the relationship between the correct curve and the attacker selected curve. With enough leaked data the Chinese remainder theorem can be used to recover the full private key. Version 4.11.0 fixes the issue.