Arm: Trustzone
- doc
- Enforcing Isolation
- devices
- Trusted Base System Architecture (TBSA)
- software architecture
- boot and chain of trust
- example use case
doc
核心是区分了Non-Secure, Secure的Physical Address Space
Translation Lookaside Buffer: Tag, Translation Regime(EL1, EL2, …), NS (1, 0), VMID, ASID, Descriptor
SMC: Secure Monitor Call
Enforcing Isolation
Secure, Non-Secure, Boot time configurable (启动时配置device是S/NS), Trustzone aware
Trustzone aware => Trustzone Address Space Controller (TZASC) => 分配DDR
balance cost, usability and security
devices
OTP(one-time programmable memory) or fuse
Non-volatile counter: anti-rollback
Trusted ROM: first boot code, attacker cannot replace it. can not reprogram it.
Trusted RAM: SRAM, on-chip, running in secure state, attack hard to gain access to its content.
Trusted Base System Architecture (TBSA)
guidelines for system designers
software architecture
软件架构图比较关键。
user-space application 不会直接访问trustzone，而是通过service api library调用。
srvice library <-> trusted service 之间通过message queues / mailboxes in memory 通信。
注意，Non-secure state can only see Non-secure memory.
有一些driver通过secure state, 底层EL3的smc传递到Trusted Kernel.
boot and chain of trust
first stage: boot ROM, 主要是load and verify { second stage boot code from flash } -> second stage: boot code from flash, 一般为off-chip dram建立memory Controller。load and verify { the images that will run in secure and non-secure state }, 例如TEE, UEFI. -> third: TEE -> third: UEFI -> OS/hypervisor
Trusted Board Boot Requirement (TBBR)
example use case
encrypted file system
authentication 之后，encrypted filesystem key 被读入 on-chip secure memory。使用master device unique key解密后，存储于on-chip.
filesystem key is provisioned, 只能由crypto engine / memory controller 安全访问
the provisioned key is used for filesystem encrypt/decrypt
Trustzone never expose the filesystem keys to Non-secure state software.
