Manually patch ret instruction for LVI

Author: Jethro Beekman

src/probestack.rs

@@ -109,8 +109,22 @@ macro_rules! define_rust_probestack {
 //
 // The ABI here is that the stack frame size is located in `%rax`. Upon
 // return we're not supposed to modify `%rsp` or `%rax`.
+#[cfg(all(
+    target_arch = "x86_64",
+    not(all(target_env = "sgx", target_vendor = "fortanix"))
+))]
+macro_rules! ret ( () => ( "ret" ) );
+#[cfg(all(
+    target_arch = "x86_64",
+    all(target_env = "sgx", target_vendor = "fortanix")
+))]
+macro_rules! ret ( () => ( "
+    pop %r11
+    lfence
+    jmp *%r11
+" ) );
 #[cfg(target_arch = "x86_64")]
-global_asm!(define_rust_probestack!(
+global_asm!(define_rust_probestack!(concat!(
     "
     .cfi_startproc
     pushq  %rbp
@@ -158,10 +172,12 @@ global_asm!(define_rust_probestack!(
     leave
     .cfi_def_cfa_register %rsp
     .cfi_adjust_cfa_offset -8
-    ret
+    ",
+    ret!(),
+    "
     .cfi_endproc
     "
-));
+)));
 
 #[cfg(target_arch = "x86")]
 // This is the same as x86_64 above, only translated for 32-bit sizes. Note