Check SGX availability

sgx_avail.c

#include <stdio.h>

/*
 * This program checks SGX availability by checking CPUID
 * Relevant spec sections: 1.7 (and 1.7.1 and 1.7.2)
 * 2015-08-14 Nico Weichbrodt
 */

/*
 * Helper function for CPUID querying
 */
void cpuid(int eax, int ecx, int *eax_out, int *ebx_out, int *ecx_out, int *edx_out)
{
    asm("pushq %%rbx\n\t"
        "cpuid\n\t"
        "movl %%ebx,%1\n\t"
        "popq %%rbx\n\t"
        : "=a"(*eax_out), "=r"(*ebx_out), "=c"(*ecx_out), "=d"(*edx_out)
        : "a"(eax), "c"(ecx));
    printf("EAX: %x\nEBX: %x\nECX: %x\nEDX: %x\n", *eax_out, *ebx_out, *ecx_out, *edx_out);
}

typedef struct
{
    int fsgsbase:1;
    int reserved1:1;
    int sgx:1;
    int bmi1:1;
    int hle:1;
    int avx2:1;
    int reserved6:1;
    int smep:1;
    int bmi2:1;
    int erms:1;
    int invpcid:1;
    int rtm:1;
    int reserved12:1;
    int reserved13:1;
    int mpx:1;
    int reserved15:1;
    int avx512f:1;
    int avx512dq:1;
    int rdseed:1;
    int adx:1;
    int smap:1;
    int avx512ifma:1;
    int pcommit:1;
    int clflushopt:1;
    int clwb:1;
    int intel_processor_trace:1;
    int avx512pf:1;
    int avx512er:1;
    int avx512cd:1;
    int sha:1;
    int avx512bw:1;
    int avx512vl:1;
} sgx_cap_7_0_ebx_t;

typedef struct
{
    int sgxv1:1;
    int sgxv2:1;
    int reserved:30;
} sgx_cap_12_0__eax_t;


int main()
{
    int eax_out, ebx_out, ecx_out, edx_out;

    // Check general SGX availability
    cpuid(0x07, 0x00, &eax_out, &ebx_out, &ecx_out, &edx_out);

    // Bit 2 of EBX informs of SGX availability.
    // The spec does not say if they count from 0 or 1, but looking at the tables 1-4, 1-5 and 1-6
    // I assume they start counting at 0.
    sgx_cap_7_0_ebx_t *sgx_avail = (sgx_cap_7_0_ebx_t *) &ebx_out;

    printf("SGX availability: %d\n", sgx_avail->sgx);
    if (!sgx_avail->sgx)
    {
        return 0;
    }

    // Check which SGX version is supported
    cpuid(0x12, 0x00, &eax_out, &ebx_out, &ecx_out, &edx_out);
    sgx_cap_12_0__eax_t *sgx_version = (sgx_cap_12_0__eax_t *) &eax_out;

    printf("SGX v1 support: %d\nSGX v2 support: %d\n", sgx_version->sgxv1, sgx_version->sgxv2);
}