Linux SGX(Intel Software Guard Extension) Support

Build WAMR vmcore (iwasm) for Linux SGX

First of all please install the Intel SGX SDK, v2.8 or later is required, and it is recommended to install the SDK to /opt/intel/sgxsdk.

After installing the dependencies, build the source code:

source <SGX_SDK dir>/environment
cd product-mini/platforms/linux-sgx/
mkdir build && cd build
cmake ..
make

By default the fast interpreter and AOT is enabled. If to enable Fast JIT, run:

mkdir build && cd build
cmake .. -DWAMR_BUILD_FAST_JIT=1
make

This builds two libraries required by SGX application:

• libvmlib.a for Enclave part

• libvmlib_untrusted.a for App part

Note: WAMR provides some features which can be easily configured by passing options to cmake, please see WAMR vmcore cmake building configurations for the details. Currently in Linux SGX, fast interpreter, AOT, libc-builtin, libc-WASI and lib-pthread are enabled by default.

Then build the enclave sample:

source <SGX_SDK dir>/environment
cd enclave-sample
make

Note: By default, the generated SGX application assumes it is signed with production key and running on simulation mode. The user can explicitly specify the relative variables in commandline to overwrite the default settings. For example, to build a debug enclave, please build the enclave with make SGX_DEBUG=1. To build the enclave running on a hardware-based SGX platform, execute make SGX_MODE=HW.

The binary file iwasm will be generated. To run the sample:

source <SGX_SDK dir>/environment
iwasm [-options] wasm_file [args...]
or:
iwasm [-options] aot_file [args...]

Minimal build

The libc-WASI and lib-pthread features require a lot of ocalls, if you don't need so much ocalls in your application, you can use the minimal version

# replace the build files with minimal version
cd product-mini/platforms/linux-sgx/
cp CMakeLists_minimal.txt CMakeLists.txt
cp enclave-sample/Makefile_minimal enclave-sample/Makefile
cp enclave-sample/Enclave/Enclave_minimal.edl enclave-sample/Enclave/Enclave.edl
# follow the building process above

Port WAMR vmcore for Linux SGX

The enclave-sample creates a sample to embed wamr vmlib of Enclave part and App part to an SGX application. To port WAMR vmcore lib to SGX application, there are some steps to do:

Step 1: Add "sgx_wamr.edl" and "sgx_pthread.edl" into EDL file, e.g. Enclave.edl:

This step is not required in minimal version

from "sgx_pthread.edl" import *;
from "sgx_wamr.edl" import *;

The sgx_wamr.edl is under ${WAMR_ROOT}/core/shared/platform/linux-sgx, so please add it to the search path list when generating Enclave_u.c and Enclave_t.c from Enclave.edl:

@cd App && $(SGX_EDGER8R) --untrusted ../Enclave/Enclave.edl \
        --search-path ../Enclave \
        --search-path $(SGX_SDK)/include \
        --search-path $(WAMR_ROOT)/core/shared/platform/linux-sgx

@cd Enclave && $(SGX_EDGER8R) --trusted ../Enclave/Enclave.edl \
        --search-path ../Enclave \
        --search-path $(SGX_SDK)/include \
        --search-path $(WAMR_ROOT)/core/shared/platform/linux-sgx

Step 2: Link libvmlib.a to Enclave part and link libvmlib_untrusted.a to App part:

libvmlib_untrusted.a is not required in minimal version

Enclave_Link_Flags := ... libvmlib.a ...

App_Link_Flags := ... libvmlib_untrusted.a ...

And link SGX pthread lib to Enclave part:

SGX pthread lib is not required in minimal version

Enclave_Link_Flags := ... -lsgx_pthread ...

Step 3: Add WAMR folders and SGX SDK folders to Enclave include path:

Enclave_Include_Paths := ... -I$(WAMR_ROOT)/core/iwasm/include \
                         -I$(WAMR_ROOT)/core/shared/utils \
                         -I$(WAMR_ROOT)/core/shared/platform/linux-sgx \
                         -I$(SGX_SDK)/include \
                         -I$(SGX_SDK)/include/tlibc \
                         -I$(SGX_SDK)/include/stlport

Step 4: Configure reserved memory and thread info in file Enclave config file (e.g. Enclave.config.xml) to support WAMR AOT and multi-thread, e.g:

<ReservedMemMaxSize>0x400000</ReservedMemMaxSize>
<ReservedMemExecutable>1</ReservedMemExecutable>
<TCSNum>10</TCSNum>

Step 5: To support log output and os_printf() function in Enclave, please implement an ocall_print function, e.g. in Enclave.edl, add:

untrusted {
    void ocall_print([in, string]const char* str);
};

In App part, add:

void
ocall_print(const char* str)
{
    printf("%s", str);
}

And in Enclave part, set the print function:

#include "wasm_export.h"
#include "bh_platform.h"

extern "C" {
    typedef void (*os_print_function_t)(const char* message);
    extern void os_set_print_function(os_print_function_t pf);

    void
    enclave_print(const char *message)
    {
        ocall_print(message);
    }
}

// In the beginning of Enclave initialization, add:
os_set_print_function(enclave_print);

Embed WAMR vmcore in Linux SGX

Normally we can embed WAMR vmcore in Linux SGX by calling the vmcore exported API's, see Embed WAMR guide for the details. And the the ecall_iwasm_main() function in file Enclave.cpp of enclave-sample also provides sample to invoke wasm app main function with wasm file buffer:

void
ecall_iwasm_main(uint8_t *wasm_file_buf, uint32_t wasm_file_size);

The enclave-sample also wraps an ecall function to receive commands from App to Enclave, and handle the commands in Enclave by calling the related WAMR vmcore API. The commands and related API's are:

typedef enum EcallCmd {
    CMD_INIT_RUNTIME = 0,     /* wasm_runtime_init/full_init() */
    CMD_LOAD_MODULE,          /* wasm_runtime_load() */
    CMD_INSTANTIATE_MODULE,   /* wasm_runtime_instantiate() */
    CMD_LOOKUP_FUNCTION,      /* wasm_runtime_lookup_function() */
    CMD_CREATE_EXEC_ENV,      /* wasm_runtime_create_exec_env() */
    CMD_CALL_WASM,            /* wasm_runtime_call_wasm */
    CMD_EXEC_APP_FUNC,        /* wasm_application_execute_func() */
    CMD_EXEC_APP_MAIN,        /* wasm_application_execute_main() */
    CMD_GET_EXCEPTION,        /* wasm_runtime_get_exception() */
    CMD_DEINSTANTIATE_MODULE, /* wasm_runtime_deinstantiate() */
    CMD_UNLOAD_MODULE,        /* wasm_runtime_unload() */
    CMD_DESTROY_RUNTIME,      /* wasm_runtime_destroy() */
    CMD_SET_WASI_ARGS,        /* wasm_runtime_set_wasi_args() */
    CMD_SET_LOG_LEVEL,        /* bh_log_set_verbose_level() */
};

SGX Intel Protected File System

Intel SGX introduced a feature called Intel Protection File System Library (IPFS) to create, operate and delete files inside the enclave. WAMR supports the mapping of IPFS on WASI functions related to file interactions, providing seamless persistence with confidentiality and integrity to the hosted WebAssembly applications in the enclave.

The usage of SGX IPFS is an optional feature. To opt-in, the support of IPFS requires the following changes:

• set the flag WAMR_BUILD_SGX_IPFS=1 when running cmake,

• the enclave must be linked with the trusted IPFS library (-lsgx_tprotected_fs),

• the application outside of the enclave must be linked with the untrusted IPFS library (-lsgx_uprotected_fs),

• the EDL file must include the following import statement:

from "sgx_tprotected_fs.edl" import *;

When using the enclave-sample project, setting the flag WAMR_BUILD_SGX_IPFS=1 when running cmake enables these changes automatically.

Verification of SGX IPFS

One can observe the usage of IPFS by running the file sample WebAssembly application. Enabling the SGX IPFS on this sample project leads to the generation of an encrypted text file.

Mapping of WASI/POSIX to IPFS

This table summarizes how WASI is mapped to POSIX and IPFS. Since IPFS is a subset of the WASI/POSIX, emulation is performed to fill the missing implementation.

WASI	POSIX	IPFS
fd_read	readv	sgx_fread
fd_write	writev	sgx_fwrite
fd_close	close	sgx_fclose
path_open	openat	sgx_fopen
fd_datasync	fsync	sgx_fflush
fd_tell	lseek	sgx_ftell
fd_filestat_set_size	ftruncate	Shrinking files is not supported, nor emulated. Extending files is emulated using sgx_fseek/sgx_ftell/sgx_fwrite.
fd_seek	lseek	The POSIX and IPFS behaviors differ. Emulated using sgx_fseek/sgx_ftell/sgx_fwrite.
fd_pwrite	pwrite	Not supported. Emulated using sgx_fseek/sgx_ftell/sgx_fwrite.
fd_pread	pread	Not supported. Emulated using sgx_fseek/sgx_ftell/sgx_fread.
fd_allocate	posix_fallocate	Not supported. Emulated using sgx_fseek/sgx_ftell/sgx_fwrite/sgx_fflush.

Performance overheads

Many benchmarks have assessed the overheads caused by IPFS through WASI functions using Twine, an early and academic adaptation of WAMR in Intel SGX with WASI support. The results can be found in this paper.

Limitations

The threat model and the limitations of SGX IPFS can be found in the official documentation.

Others

• Please add "-sgx" option when generating AoT file for SGX platform, e.g.:

  wamrc -sgx -o test.aot test.wasm

• The default max heap size of Enclave is 16 MB, it might be not enough when executing some workloads, please modify it in Enclave/Enclave.config.xml with a larger size when exception was thrown:

  Exception: fail to enlarge memory.
  or
  Exception: allocate memory failed.

  Enclave/Enclave.config.xml, default max heap size is 16 MB:

  <HeapMaxSize>0x1000000</HeapMaxSize>