Time-of-check time-of-use race condition in Rockchip RK3588s

Summary

Secure BootROM of RK3588s SoC is vulnerable to a time-of-check to time-of-use attack in case of booting from external media (SPI NOR or NAND, EMMC or SD). The code reads the header of the next-stage loader twice. The header contains hashes of the executable modules and is signed with a private key, the public part of which is verified against the SHA256 digest blown in the OTP. The first read is only partial and contains only the hashes of the executable modules. The second is complete, including the header signature. Although the header is verified based on the fully read data, the authenticity of the executable modules is checked against the partial data from the first read. An attacker with physical access to a device containing RK3588s SoC can easily modify the next-stage loader data on-the-fly using a low-cost SD-card or SPI NOR/NAND or EMMC emulator. Even a simple ultra low-cost circuit comprising two memory chips (containing the same data but different headers - the original and the modified one) and a multiplexer can be used to carry out an attack. This can lead to arbitrary code execution with the highest privileges available (EL3). This issue affects RK3588s: RK3588s SoC BootROM (secure) 350B20210512V100 and possibly others. As remediation apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable https://www.rock-chips.com/a/en/products/RK35_Series/2022/0926/1660.html