Add detection for FSGSBASE enablement in PAL

src/pal/src/pal_api.c

@@ -7,6 +7,7 @@
 #include "pal_sig_handler.h"
 #include "pal_syscall.h"
 #include "pal_thread_counter.h"
+#include "pal_check_fsgsbase.h"
 #include "errno2str.h"
 #include <linux/limits.h>
 
@@ -77,6 +78,14 @@ int occlum_pal_init(const struct occlum_pal_attr *attr) {
         return -1;
     }
 
+// Check only for SGX hardware mode
+#ifdef SGX_MODE_HW
+    if (check_fsgsbase_enablement() != 0) {
+        PAL_ERROR("FSGSBASE enablement check failed.");
+        return -1;
+    }
+#endif
+
     sgx_enclave_id_t eid = pal_get_enclave_id();
     if (eid != SGX_INVALID_ENCLAVE_ID) {
         PAL_ERROR("Enclave has been initialized.");

src/pal/src/pal_check_fsgsbase.c

@@ -0,0 +1,63 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <signal.h>
+#include <assert.h>
+#include <string.h>
+#include <ucontext.h>
+#include <setjmp.h>
+#include <stdlib.h>
+#include <errno.h>
+
+#include "pal_log.h"
+#include "pal_check_fsgsbase.h"
+
+#define RC 0xffff
+static jmp_buf env_buf;
+
+static void handle_sigill(int num) {
+    assert(num == SIGILL);
+
+    longjmp(env_buf, RC);
+}
+
+int check_fsgsbase_enablement(void) {
+    int gs_read_data = 0;
+    int gs_write_data = 0x0f;
+    int __seg_gs *offset_ptr = 0;   // offset relative to GS. support since gcc-6
+
+    sighandler_t handler_orig = signal(SIGILL, handle_sigill);
+    if (handler_orig == SIG_ERR) {
+        PAL_ERROR("registering signal handler failed, errno = %d", errno);
+        return errno;
+    }
+
+    int ret = setjmp(env_buf);
+    if (ret == RC) {
+        // return from SIGILL handler
+        PAL_ERROR("\tSIGILL Caught !");
+        return -1;
+    }
+    if (ret != 0) {
+        PAL_ERROR("setjmp failed");
+        return -1;
+    }
+
+    // Check if kernel supports FSGSBASE
+    asm("rdgsbase %0" :: "r" (&gs_read_data));
+    asm("wrgsbase %0" :: "r" (&gs_write_data));
+
+    if (*offset_ptr != 0x0f) {
+        PAL_ERROR("GS register data not match\n");
+        return -1;
+    };
+
+    // Restore the GS register and original signal handler
+    asm("wrgsbase %0" :: "r" (&gs_read_data));
+    handler_orig = signal(SIGILL, handler_orig);
+    if (handler_orig == SIG_ERR) {
+        PAL_ERROR("restoring default signal handler failed, errno = %d", errno);
+        return errno;
+    }
+
+    return 0;
+}

src/pal/src/pal_check_fsgsbase.h

@@ -0,0 +1,8 @@
+#ifndef __PAL_CHECK_FSGSBASE_H__
+#define __PAL_CHECK_FSGSBASE_H__
+
+// Check if FSGSBASE instructions are supported.
+// Return 0 if the check pass.
+int check_fsgsbase_enablement(void);
+
+#endif