[Pal/Linux-SGX] Drop unused SGX_HAS_FSGSBASE flag

SGX_HAS_FSGSBASE has been hardcoded to 1 since the beginning.

Also the Intel SDM doesn't mention that the FS/GS handling in SGX can be
unavailable on some hardware.

So just drop it.

Closes #545.

Pal/src/host/Linux-SGX/db_exception.c

@@ -190,13 +190,6 @@ void restore_sgx_context (sgx_context_t * uc)
 
 void _DkExceptionHandler (unsigned int exit_info, sgx_context_t * uc)
 {
-#if SGX_HAS_FSGSBASE == 0
-    /* set the FS first if necessary */
-    uint64_t fsbase = (uint64_t) GET_ENCLAVE_TLS(fsbase);
-    if (fsbase)
-        wrfsbase(fsbase);
-#endif
-
     union {
         sgx_arch_exitinfo_t info;
         int intval;

Pal/src/host/Linux-SGX/enclave_entry.S

@@ -97,26 +97,6 @@ enclave_entry:
 	cmpl $0, %edi
 	jne .Lhandle_exception
 
-#if SGX_HAS_FSGSBASE == 0
-	movq %gs:SGX_FSBASE, %rdi
-	cmpq $0, %rdi
-	je .Ljust_resume
-
-	movq SGX_GPR_RSP(%rbx), %rsi
-	subq $16, %rsi
-	movq %rsi, SGX_GPR_RSP(%rbx)
-
-	# try to push rip and fsbase onto the stack
-	movq %rdi, (%rsi)
-	movq SGX_GPR_RIP(%rbx), %rdi
-	movq %rdi, 8(%rsi)
-
-	# new RIP is the resume point
-	leaq .Lafter_resume(%rip), %rdi
-	movq %rdi, SGX_GPR_RIP(%rbx)
-
-.Ljust_resume:
-#endif
 	# clear the registers
 	xorq %rdi, %rdi
 	xorq %rsi, %rsi
@@ -126,15 +106,6 @@ enclave_entry:
 	movq $EEXIT, %rax
 	ENCLU
 
-#if SGX_HAS_FSGSBASE == 0
-.Lafter_resume:
-	movq %rbx, -8(%rsp)
-	popq %rbx
-	.byte 0xf3, 0x48, 0x0f, 0xae, 0xd3 /* WRFSBASE %RBX */
-	movq -16(%rsp), %rbx
-	retq
-#endif
-
 	## There is a race between host signal delivery and restoring %rsp
 	## in this entry code. We must be careful to setup %rsp.
 	##

Pal/src/host/Linux-SGX/pal_linux_defs.h

@@ -15,8 +15,6 @@
 #define DEBUG_ECALL         (0)
 #define DEBUG_OCALL         (0)
 
-#define SGX_HAS_FSGSBASE    (1)
-
 #define TRUSTED_STUB_SIZE   (PRESET_PAGESIZE * 4)
 
 #define CACHE_FILE_STUBS    (1)

Pal/src/host/Linux-SGX/sgx_arch.h

@@ -101,10 +101,8 @@ typedef struct {
     uint64_t urbp;
     uint32_t exitinfo;
     uint32_t reserved;
-#if SGX_HAS_FSGSBASE == 1
     uint64_t fsbase;
     uint64_t gsbase;
-#endif
 } sgx_arch_gpr_t;
 
 typedef struct {

Pal/src/host/Linux-SGX/sgx_entry.S

@@ -26,38 +26,6 @@ sgx_ecall:
 	.global async_exit_pointer
 	.type async_exit_pointer, @function
 
-#if SGX_HAS_FSGSBASE == 0
-async_exit_pointer:
-	# because ERESUME doesn't restore FS/GS, we must do EENTER
-
-	movq current_tcs@gottpoff(%rip), %rbx
-	movq %fs:(%rbx), %rbx
-
-	leaq double_async_exit(%rip), %rcx
-
-	# put the exit address in RDX
-	leaq .Lreal_resume(%rip), %rdx
-
-	movq $EENTER, %rax
-	ENCLU
-
-.Lreal_resume:
-	# RBX has to be the TCS of the thread
-	movq current_tcs@gottpoff(%rip), %rbx
-	movq %fs:(%rbx), %rbx
-
-	# RCX has to be the AEP (Asynchronous Exit Pointer)
-	leaq async_exit_pointer(%rip), %rcx
-
-	movq $ERESUME, %rax
-	ENCLU
-
-	.global double_async_exit
-	.type double_async_exit, @function
-
-double_async_exit:
-	ENCLU
-#else
 async_exit_pointer:
 	ENCLU
 
@@ -70,7 +38,6 @@ sgx_raise:
 
 .Lafter_resume:
 	retq
-#endif
 
 sgx_entry:
 	# arguments: RDI - code, RSI - ms

Pal/src/host/Linux-SGX/sgx_exception.c

@@ -204,21 +204,12 @@ static void _DkTerminateSighandler (int signum, siginfo_t * info,
 {
     unsigned long rip = uc->uc_mcontext.gregs[REG_RIP];
 
-#if SGX_HAS_FSGSBASE == 0
-    if (rip != (unsigned long) async_exit_pointer &&
-        rip != (unsigned long) double_async_exit) {
-#else
     if (rip != (unsigned long) async_exit_pointer) {
-#endif
         uc->uc_mcontext.gregs[REG_RIP] = (uint64_t) sgx_entry_return;
         uc->uc_mcontext.gregs[REG_RDI] = -PAL_ERROR_INTERRUPTED;
         uc->uc_mcontext.gregs[REG_RSI] = get_event_num(signum);
     } else {
-#if SGX_HAS_FSGSBASE != 0
         sgx_raise(get_event_num(signum));
-#else
-        uc->uc_mcontext.gregs[REG_R9]  = get_event_num(signum);
-#endif
     }
 }
 
@@ -227,12 +218,7 @@ static void _DkResumeSighandler (int signum, siginfo_t * info,
 {
     unsigned long rip = uc->uc_mcontext.gregs[REG_RIP];
 
-#if SGX_HAS_FSGSBASE == 0
-    if (rip != (unsigned long) async_exit_pointer &&
-        rip != (unsigned long) double_async_exit) {
-#else
     if (rip != (unsigned long) async_exit_pointer) {
-#endif
         switch (signum) {
             case SIGSEGV:
                 SGX_DBG(DBG_E, "Segmentation Fault in Untrusted Code (RIP = %08lx)\n", rip);
@@ -254,11 +240,7 @@ static void _DkResumeSighandler (int signum, siginfo_t * info,
     }
 
     int event = get_event_num(signum);
-#if SGX_HAS_FSGSBASE != 0
     sgx_raise(event);
-#else
-    uc->uc_mcontext.gregs[REG_R9] = event;
-#endif
 }
 
 int sgx_signal_setup (void)

Pal/src/host/Linux-SGX/sgx_internal.h

@@ -112,9 +112,6 @@ int sgx_ecall (long ecall_no, void * ms);
 int sgx_raise (int event);
 
 void async_exit_pointer (void);
-#if SGX_HAS_FSGSBASE == 0
-void double_async_exit (void);
-#endif
 
 int interrupt_thread (void * tcs);
 int clone_thread (void);