Add LLVM CFI support to the Rust compiler

This commit adds LLVM Control Flow Integrity (CFI) support to the Rust
compiler. It initially provides forward-edge control flow protection for
Rust-compiled code only by aggregating function pointers in groups
identified by their number of arguments.

Forward-edge control flow protection for C or C++ and Rust -compiled
code "mixed binaries" (i.e., for when C or C++ and Rust -compiled code
share the same virtual address space) will be provided in later work as
part of this project by defining and using compatible type identifiers
(see Type metadata in the design document in the tracking issue #89653).

LLVM CFI can be enabled with -Zsanitizer=cfi and requires LTO (i.e.,
-Clto).

compiler/rustc_codegen_llvm/src/builder.rs

@@ -604,6 +604,32 @@ impl BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         }
     }
 
+    fn type_metadata(&mut self, function: &'ll Value, typeid: String) {
+        let typeid_metadata = self.typeid_metadata(typeid);
+        let v = [self.const_usize(0), typeid_metadata];
+        unsafe {
+            llvm::LLVMGlobalSetMetadata(
+                function,
+                llvm::MD_type as c_uint,
+                llvm::LLVMValueAsMetadata(llvm::LLVMMDNodeInContext(
+                    self.cx.llcx,
+                    v.as_ptr(),
+                    v.len() as c_uint,
+                )),
+            )
+        }
+    }
+
+    fn typeid_metadata(&mut self, typeid: String) -> Self::Value {
+        unsafe {
+            llvm::LLVMMDStringInContext(
+                self.cx.llcx,
+                typeid.as_ptr() as *const c_char,
+                typeid.as_bytes().len() as c_uint,
+            )
+        }
+    }
+
     fn store(&mut self, val: &'ll Value, ptr: &'ll Value, align: Align) -> &'ll Value {
         self.store_with_flags(val, ptr, align, MemFlags::empty())
     }

compiler/rustc_codegen_llvm/src/context.rs

@@ -221,6 +221,15 @@ pub unsafe fn create_module(
         llvm::LLVMRustAddModuleFlag(llmod, avoid_plt, 1);
     }
 
+    if sess.is_sanitizer_cfi_enabled() {
+        // FIXME(rcvalle): Add support for non canonical jump tables.
+        let canonical_jump_tables = "CFI Canonical Jump Tables\0".as_ptr().cast();
+        // FIXME(rcvalle): Add it with Override behavior flag--LLVMRustAddModuleFlag adds it with
+        // Warning behavior flag. Add support for specifying the behavior flag to
+        // LLVMRustAddModuleFlag.
+        llvm::LLVMRustAddModuleFlag(llmod, canonical_jump_tables, 1);
+    }
+
     // Control Flow Guard is currently only supported by the MSVC linker on Windows.
     if sess.target.is_like_msvc {
         match sess.opts.cg.control_flow_guard {
@@ -779,6 +788,8 @@ impl CodegenCx<'b, 'tcx> {
             ifn!("llvm.instrprof.increment", fn(i8p, t_i64, t_i32, t_i32) -> void);
         }
 
+        ifn!("llvm.type.test", fn(i8p, self.type_metadata()) -> i1);
+
         if self.sess().opts.debuginfo != DebugInfo::None {
             ifn!("llvm.dbg.declare", fn(self.type_metadata(), self.type_metadata()) -> void);
             ifn!("llvm.dbg.value", fn(self.type_metadata(), t_i64, self.type_metadata()) -> void);

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -401,6 +401,14 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
         }
     }
 
+    fn type_test(&mut self, pointer: Self::Value, typeid: Self::Value) -> Self::Value {
+        // Test the called operand using llvm.type.test intrinsic. The LowerTypeTests link-time
+        // optimization pass replaces calls to this intrinsic with code to test type membership.
+        let i8p_ty = self.type_i8p();
+        let bitcast = self.bitcast(pointer, i8p_ty);
+        self.call_intrinsic("llvm.type.test", &[bitcast, typeid])
+    }
+
     fn va_start(&mut self, va_list: &'ll Value) -> &'ll Value {
         self.call_intrinsic("llvm.va_start", &[va_list])
     }

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -389,6 +389,7 @@ pub enum MetadataType {
     MD_nontemporal = 9,
     MD_mem_parallel_loop_access = 10,
     MD_nonnull = 11,
+    MD_type = 19,
 }
 
 /// LLVMRustAsmDialect
@@ -975,6 +976,8 @@ extern "C" {
     pub fn LLVMSetValueName2(Val: &Value, Name: *const c_char, NameLen: size_t);
     pub fn LLVMReplaceAllUsesWith(OldVal: &'a Value, NewVal: &'a Value);
     pub fn LLVMSetMetadata(Val: &'a Value, KindID: c_uint, Node: &'a Value);
+    pub fn LLVMGlobalSetMetadata(Val: &'a Value, KindID: c_uint, Metadata: &'a Metadata);
+    pub fn LLVMValueAsMetadata(Node: &'a Value) -> &Metadata;
 
     // Operations on constants of any type
     pub fn LLVMConstNull(Ty: &Type) -> &Value;