sgxutils.c

#include <unistd.h>
#include <stdint.h>
#include <stdbool.h>
#include "sgx.h"

static inline void cpuid(int *eax, int *ebx, int *ecx, int *edx)
{
#if defined(__x86_64__)
	asm volatile ("cpuid"
		: "=a" (*eax),
		"=b" (*ebx),
		"=c" (*ecx),
		"=d" (*edx)
		: "0" (*eax), "2" (*ecx)
		: "memory");
#else
	/*on 32bit, ebx can NOT be used as PIC code*/
	asm volatile ("xchgl %%ebx, %1; cpuid; xchgl %%ebx, %1"
		: "=a" (*eax), "=r" (*ebx), "=c" (*ecx), "=d" (*edx)
		: "0" (*eax), "2" (*ecx)
		: "memory");
#endif
}

static inline void __cpuid(int a[4], int b)
{
    a[0] = b;
    a[2] = 0;
    cpuid(&a[0], &a[1], &a[2], &a[3]);
}

static inline void __cpuidex(int a[4], int b, int c)
{
    a[0] = b;
    a[2] = c;
    cpuid(&a[0], &a[1], &a[2], &a[3]);
}

static inline uint64_t xgetbv(uint32_t index)
{
    uint32_t eax, edx;

    asm volatile(".byte 0x0f,0x01,0xd0" /* xgetbv */
		: "=a" (eax), "=d" (edx)
		: "c" (index));

    return eax + ((uint64_t)edx << 32);
}

static inline uint64_t get_xcr0()
{
    return xgetbv(0);
}

static bool try_get_xcr0(uint64_t *value)
{
    int cpu_info[4] = {0, 0, 0, 0};

    *value = SGX_XFRM_LEGACY;

    // check if xgetbv instruction is supported
    __cpuid(cpu_info, 1);
    // ecx[27:26] indicate whether support xsave/xrstor, and whether enable xgetbv, xsetbv
    if (!(cpu_info[2] & (1<<XSAVE_SHIFT)) || !(cpu_info[2] & (1<<OSXSAVE_SHIFT)))
        return false;

    *value = get_xcr0();

    // check if xsavec is supported
    // Assume that XSAVEC is always supported if XSAVE is supported
    cpu_info[0] = cpu_info[1] = cpu_info[2] = cpu_info[3] = 0;
    __cpuidex(cpu_info, 0xD, 1);
    if (!(cpu_info[0] & (1<<XSAVEC_SHIFT)))
        return false;

    return true;
}

void get_sgx_xfrm_by_cpuid(uint64_t *xfrm)
{
    int cpu_info[4] = {0, 0, 0, 0};

    __cpuidex(cpu_info, SGX_LEAF, 1);

    if (false == try_get_xcr0(xfrm))
    {
	// if XSAVE is supported, while XSAVEC is not supported,
	// set xfrm to legacy, because XSAVEC cannot be executed within enclave.
	*xfrm = SGX_XFRM_LEGACY;
    } else {
	// If x-feature is supported and enabled by OS, we need make sure it is also supported in enclave.
	*xfrm &= (((uint64_t)cpu_info[3] << 32) | cpu_info[2]);
    }
}