Snippets part of DWSec blog:

check_sip.c

uint32_t get_sip(void) {
    const char *sip_path = "/usr/lib/libSystem.dylib";
    const char *sip_function = "csr_get_active_config";

    void *libSystem = dlopen(sip_path, RTLD_LAZY);
    if (!libSystem) {
        printf("get_sip: Error loading libSystem.dylib\n");
        return -1;
    };

    void *csr_get_active_config = dlsym(libSystem, sip_function);
    if (!csr_get_active_config) {
        printf("get_sip: Error loading csr_get_active_config\n");
        return -1;
    };

    int (*csr_get_active_config_ptr)(uint32_t *) = (int (*)(uint32_t *))csr_get_active_config;
    uint32_t sip = 0;
    int err = csr_get_active_config_ptr(&sip);
    if (err) {
        printf("get_sip: Error calling csr_get_active_config\n");
        return -1;
    };

    dlclose(libSystem);

    return sip;
}

bool is_sip_enabled(uint32_t sip){
   return sip ? false : true;
}

csr.h

/* CSR configuration flags */
#define CSR_ALLOW_UNTRUSTED_KEXTS               (1 << 0)
#define CSR_ALLOW_UNRESTRICTED_FS               (1 << 1)
#define CSR_ALLOW_TASK_FOR_PID                  (1 << 2)
#define CSR_ALLOW_KERNEL_DEBUGGER               (1 << 3)
#define CSR_ALLOW_APPLE_INTERNAL                (1 << 4)
#define CSR_ALLOW_DESTRUCTIVE_DTRACE                    (1 << 5) /* name deprecated */
#define CSR_ALLOW_UNRESTRICTED_DTRACE                   (1 << 5)
#define CSR_ALLOW_UNRESTRICTED_NVRAM                    (1 << 6)
#define CSR_ALLOW_DEVICE_CONFIGURATION                  (1 << 7)
#define CSR_ALLOW_ANY_RECOVERY_OS                       (1 << 8)
#define CSR_ALLOW_UNAPPROVED_KEXTS                      (1 << 9)
#define CSR_ALLOW_EXECUTABLE_POLICY_OVERRIDE    (1 << 10)
#define CSR_ALLOW_UNAUTHENTICATED_ROOT                  (1 << 11)

#define CSR_VALID_FLAGS (CSR_ALLOW_UNTRUSTED_KEXTS | \
	                         CSR_ALLOW_UNRESTRICTED_FS | \
	                         CSR_ALLOW_TASK_FOR_PID | \
	                         CSR_ALLOW_KERNEL_DEBUGGER | \
	                         CSR_ALLOW_APPLE_INTERNAL | \
	                         CSR_ALLOW_UNRESTRICTED_DTRACE | \
	                         CSR_ALLOW_UNRESTRICTED_NVRAM | \
	                         CSR_ALLOW_DEVICE_CONFIGURATION | \
	                         CSR_ALLOW_ANY_RECOVERY_OS | \
	                         CSR_ALLOW_UNAPPROVED_KEXTS | \
	                         CSR_ALLOW_EXECUTABLE_POLICY_OVERRIDE | \
	                         CSR_ALLOW_UNAUTHENTICATED_ROOT)

#define CSR_ALWAYS_ENFORCED_FLAGS (CSR_ALLOW_DEVICE_CONFIGURATION | CSR_ALLOW_ANY_RECOVERY_OS)

/* Flags set by `csrutil disable`. */
#define CSR_DISABLE_FLAGS (CSR_ALLOW_UNTRUSTED_KEXTS | \
	                   CSR_ALLOW_UNRESTRICTED_FS | \
	                   CSR_ALLOW_TASK_FOR_PID | \
	                   CSR_ALLOW_KERNEL_DEBUGGER | \
	                   CSR_ALLOW_APPLE_INTERNAL | \
	                   CSR_ALLOW_UNRESTRICTED_DTRACE | \
	                   CSR_ALLOW_UNRESTRICTED_NVRAM)

/* CSR capabilities that a booter can give to the system */
#define CSR_CAPABILITY_UNLIMITED                        (1 << 0)
#define CSR_CAPABILITY_CONFIG                           (1 << 1)
#define CSR_CAPABILITY_APPLE_INTERNAL                   (1 << 2)

#define CSR_VALID_CAPABILITIES (CSR_CAPABILITY_UNLIMITED | CSR_CAPABILITY_CONFIG | CSR_CAPABILITY_APPLE_INTERNAL)