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internal commit: 14ac2bc2299032fa6714d1fefa7cf0987b3e3085 Signed-off-by: Eddie Dong <eddie.dong@intel.com>
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Eddie Dong
lijinxia
157
hypervisor/Documentation/Trusty.txt
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157
hypervisor/Documentation/Trusty.txt
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Trusty on ACRN
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Overview
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Trusty Architecture
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Trusty specific Hypercalls
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Trusty Boot flow
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EPT Hierarchy
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********
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Overview
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********
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Trusty is a set of software components supporting a Trusted Execution Environment (TEE).
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Trusty consists of:
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1. An operating system (the Trusty OS) that runs on a processor intended to provide a TEE
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2. Drivers for the Android kernel (Linux) to facilitate communication with applications
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running under the Trusty OS
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3. A set of libraries for Android/Linux systems software to facilitate communication with
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trusted applications executed within the Trusty OS using the kernel drivers
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LK (Little Kernel) is a tiny operating system suited for small embedded devices, bootloaders,
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and other environments where OS primitives like threads, mutexes, and timers are needed, but
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there's a desire to keep things small and lightweight. LK has been chosen as the Trusty OS kernel.
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*******************
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Trusty Architecture
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*******************
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+---------------------------+
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|VMn |
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| ...... |
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+------------+ +---------------------------+ |
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|VM0 | |VM1 | |
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| | | +--------+ +--------+ | |
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| | | | | | | | |
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| SOS | | | Normal | | Secure | | |
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| | | | World | | World | |-+
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| | | | | | | |
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| | | +--------+ +--------+ |
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+------------+ +---------------------------+
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+-------------------------------------------+
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| ACRN Hypervisor |
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+-------------------------------------------+
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+-------------------------------------------+
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| HW |
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+-------------------------------------------+
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Note: Trusty OS is running in Secure World in the architecture above.
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**************************
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Trusty specific Hypercalls
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**************************
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1. HC_LAUNCH_TRUSTY
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->This Hypercall is used by UOSloader to request ACRN to launch Trusty.
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->The Trusty memory region range, entry point must be specified.
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->Hypervisor needs to save current vCPU contexts (Normal World).
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2. HC_WORLD_SWITCH
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->Simulate ARM SMC (Secure Monitor Call, or SMC) instruction to do world switch.
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->Hypervisor needs to save current world vCPU contexts, and load next world vCPU contexts.
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->Update rdi, rsi, rdx, rbx to next world vCPU contexts.
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API
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---
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1. hcall_launch_trusty(vm_t *vm);
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2. hcall_world_switch(vm_t *vm);
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****************
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Trusty Boot flow
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****************
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Per design, AOSloader will trigger boot of Trusty. So the boot flow will be:
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AOSloader --> ACRN --> Trusty --> ACRN --> AOSloader
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Detail:
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1. UOSloader
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1.1 load and verify trusty image from virtual disk.
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1.2 allocate runtime memory for trusty.
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1.3 do ELF relocation of trusty image and get entry address.
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1.4 call HC_LAUNCH_TRUSTY with trusty memory base and entry address.
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2. ACRN(HC_LAUNCH_TRUSTY)
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2.1 save World context for Normal World.
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2.2 init World context for Secure World(RIP, RSP, EPT, etc.).
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2.3 resume to Secure World.
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3. Trusty
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3.1 booting up
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3.2 call HC_WORLD_SWITCH to switch back to Normal World if boot completed.
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4. ACRN(HC_WORLD_SWITCH)
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4.1 save World context for the World which caused this vmexit(Secure World)
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4.2 restore World context for next World(Normal World(UOSloader))
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4.3 resume to next World(UOSloader)
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5. UOSloader
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5.1 continue to boot.
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*************
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EPT Hierarchy
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*************
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Per Trusty design, Trusty can access Normal World's memory, but Normal World cannot
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access Secure World's memory. Hence it means Secure World EPTP page table hierarchy
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must contain normal world GPA address space, while Trusty world's GPA address space
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must be removed from the Normal world EPTP page table hierarchy.
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Design:
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Put Secure World's GPA to very high position: 511G-512G. The PML4/PDPT for Trusty
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World are separated from Normal World. PD/PT for low memory (<511G) are shared in
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both Trusty World's EPT and Normal World's EPT. PD/PT for high memory (>=511G) are
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valid for Trusty World's EPT only.
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Benefit:
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This design will benefit the EPT changes of Normal World. There are requirement to
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modify Normal World's EPT during runtime such as memory increasing, attribute
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change, etc. If such behavior happened, only PD and PT for Normal World need to
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be updated.
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ABSTRACT EPT hierarchy for 2 Worlds:
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==================================================================== ==================================================
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: Normal World : : Secure World :
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: PML4 : : PML4 :
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: +--------+ : : +--------+ :
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: | | : : | | :
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: | | : : PD | | :
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: | | : : +-------+ | | :
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: | | : : | | | | :
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: | 0-512G |--+ : : | | +--| 0-512G | :
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:EPTP -->+--------+ | : : | | | +--------+<-- EPTP :
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: | PDPT : : | | PDPT | :
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: | +--------+ : : | | +--------+ | :
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: | | >=511G |---> Not present : : +-------+<--| >=511G | | :
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: | |________| : : |________| | :
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: | | | : : | | | :
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: | | <511G |->+<----------------------------:--------:--------------| <511G | | :
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: | | | | : : | | | :
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: +-->+--------+ | PD PT : : +--------+<-+ :
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: | ... ... : ==================================================
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: | +-------+ +-------+ :
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: | +-------+| +-------+| :
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: | | || | || :
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: | | || | || :
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: | | PDE |--+ | || :
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: | | || | | || :
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: | | |+ | | |+ :
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: +-->+-------+ +-->+-------+ :
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: :
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====================================================================
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API
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----
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/*
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Create Secure World EPT hierarchy, construct new PML4/PDPT, reuse PD/PT parse from
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vm->arch_vm->ept
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Parameters:
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vm: VM with 2 Worlds
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gpa: original gpa allocated from vSBL
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size: LK size(16M by default)
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rebase_offset: rebase the gpa to offset xxx(511G_OFFSET)
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*/
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int create_secure_world_ept(vm_t *vm, uint64_t gpa, uint64_t size, uint64_t rebase_offset)
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