⚠️ The code is based on: https://gitlab.com/riseproject/riscv-optee/opensbi/-/tree/dev-optee-mpxy

Commit ID: 7d4c90953afe3bd86f9e2501bd4c2501e8db1898

  • mpxy_opteed_init()

    • Match compatible string: "riscv,sbi-mpxy-opteed".

    • Allocate channel.

    • opteed_domain_setup()

      • Setup domain for OP-TEE dispatcher by looking up the domain specified by opensbi-domain-instance phandle in DTS.
      • Assign the domain name to opteed_domain_name.

    • Get channel ID from DTS property: riscv,sbi-mpxy-channel-id.

    • Initialize channel:

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      // lib/utils/mpxy/fdt_mpxy_opteed.c

channel->channel_id = channel_id;
channel->send_message = mpxy_opteed_send_message;
channel->attrs.msg_proto_id = SBI_MPXY_MSGPROTO_TEE_ID;
channel->attrs.msg_data_maxlen = PAGE_SIZE;

    • Register channel: sbi_mpxy_register_channel()

    • Assign tdomain (Trusted domain).

      • Look up the domain with the name specified in opteed_domain_name.

    • Assign udomain (Untrusted domain).

      • Look up the domain with the name "untrusted-domain".
  • mpxy_opteed_send_message()
    • If message ID is OPTEED_MSG_COMMUNICATE (0x1) (Called from udomain):
      • If tdomain’s shared memory is NOT valid, return SBI_EINVAL.
      • Otherwise:
        • Direction: udomain -> OpenSBI
        • Copy the source data from udomain to tdomain’s shared memory.
      • Call sbi_ecall_tee_domain_enter() to switch to tdomain.
        • Direction: udomain -> tdomain.
        • The entry point to be switched to is defined by the function type:
          • Function type is defined by the first unsigned long in udomain’s shared memory: ((ulong *)shmem_base)[0].
          • If function type is: ABI_ENTRY_TYPE_FAST (i.e. ARM_SMCCC_FAST_CALL)
          • Otherwise:
    • If message ID is OPTEED_MSG_COMPLETE (0x2) (Called from tdomain):
      • If udomain’s shared memory is NOT valid:
        • Direction: tdomain -> OpenSBI.
        • If ((ulong *)msgbuf)[0] (from tdomain’s shared memory, i.e. $a0) is TEEABI_OPTEED_RETURN_CALL_DONE (0xbe000000):
          • Register OP-TEE entry table:
            • Set entry_vector_table to ((ulong *)msgbuf)[1] (i.e. $a1), i.e. thread_vector_table defined in OP-TEE.
      • Otherwise, copy the source data from tdomain to udomain’s shared memory.
        • Direction: tdomain -> udomain.
        • Only $a1 ~ $a4 (from tdomain’s shared memory) are copied to udomain’s shared memory, $a0 is skipped.
      • Call sbi_ecall_tee_domain_exit() to exit from the current tdomain.
        • The domain to switch to:
          • Switch to the previous domain
          • Switch to the use-define next domain.
          • Fallback to the root domain.
    • P.S. Domain switching only involves domain contexts save and restore. The mode is switched by mret in the trap handler.
  • sbi_mpxy_register_channel()
    • Initialize channel’s attributes: mpxy_std_attrs_init()
      • Check whether MSI, SSE and Events State capabilities are available in the domain.
    • Add the allocated channel to mpxy_channel_list list.
  • sbi_mpxy_set_shmem()
    • Validate passed in shared memory address and size.
    • Set current hart’s sbi_domain shared memory address and size.
  • sbi_mpxy_send_message()
  • sbi_ecall_tee_domain_enter()
    • The domain is tdomain.
    • sbi_domain_context_set_mepc()
      • Set mepc to the entry point.
    • sbi_domain_context_enter()
      • Switch to tdomain.

  • Example DTS:

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        chosen {
        opensbi-domains {

            .....

            trusted-domain {
                compatible = "opensbi,domain,instance";
                regions = <0x04 0x3f>;
                possible-harts = <0x03 0x01>;
                next-addr = <0x00 0xf1000000>;
                next-mode = <0x01>;
                phandle = <0x02>;
            };

            .....
        };
    };

    sbi-mpxy-opteed {
        opensbi-domain-instance = <0x02>;
        riscv,sbi-mpxy-channel-id = <0x02>;
        compatible = "riscv,sbi-mpxy-opteed";
    };