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. Starting in version 4.5.0 and prior to version 4.11.0, the RSA-OAEP decryption implementation in the Hisilicon HPRE crypto driver uses non-constant-time memcmp() for label hash verification and has multiple distinguishable error paths. This creates a Manger-style padding oracle that allows an attacker to recover RSA-OAEP plaintext with approximately 1000-2000 adaptive chosen ciphertext queries. Only affects plat-d06 with CFG_HISILICON_ACC_V3=y, which seems to be disabled by default. Version 4.11.0 contains a patch. As a workaround, disable Hisilicon HPRE RSA driver with CFG_HISILICON_ACC_V3=n.