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).

4 files changed, 47 insertions, 3 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index b0a5631549d..8f739a264ea 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -19,6 +19,7 @@ use rustc_middle::ty::print::{with_no_trimmed_paths, with_no_visible_paths};
 use rustc_middle::ty::{self, Instance, Ty, TypeFoldable};
 use rustc_span::source_map::Span;
 use rustc_span::{sym, Symbol};
+use rustc_symbol_mangling::typeid_for_fnabi;
 use rustc_target::abi::call::{ArgAbi, FnAbi, PassMode};
 use rustc_target::abi::{self, HasDataLayout, WrappingRange};
 use rustc_target::spec::abi::Abi;
@@ -818,12 +819,43 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             self.codegen_argument(&mut bx, location, &mut llargs, last_arg);
         }
 
-        let fn_ptr = match (llfn, instance) {
-            (Some(llfn), _) => llfn,
-            (None, Some(instance)) => bx.get_fn_addr(instance),
+        let (is_indirect_call, fn_ptr) = match (llfn, instance) {
+            (Some(llfn), _) => (true, llfn),
+            (None, Some(instance)) => (false, bx.get_fn_addr(instance)),
             _ => span_bug!(span, "no llfn for call"),
         };
 
+        // For backends that support CFI using type membership (i.e., testing whether a given
+        // pointer is associated with a type identifier).
+        if bx.tcx().sess.is_sanitizer_cfi_enabled() && is_indirect_call {
+            // Emit type metadata and checks.
+            // FIXME(rcvalle): Add support for generalized identifiers.
+            // FIXME(rcvalle): Create distinct unnamed MDNodes for internal identifiers.
+            let typeid = typeid_for_fnabi(bx.tcx(), fn_abi);
+            let typeid_metadata = bx.typeid_metadata(typeid.clone());
+
+            // Test whether the function pointer is associated with the type identifier.
+            let cond = bx.type_test(fn_ptr, typeid_metadata);
+            let mut bx_pass = bx.build_sibling_block("type_test.pass");
+            let mut bx_fail = bx.build_sibling_block("type_test.fail");
+            bx.cond_br(cond, bx_pass.llbb(), bx_fail.llbb());
+
+            helper.do_call(
+                self,
+                &mut bx_pass,
+                fn_abi,
+                fn_ptr,
+                &llargs,
+                destination.as_ref().map(|&(_, target)| (ret_dest, target)),
+                cleanup,
+            );
+
+            bx_fail.abort();
+            bx_fail.unreachable();
+
+            return;
+        }
+
         helper.do_call(
             self,
             &mut bx,
diff --git a/compiler/rustc_codegen_ssa/src/mir/mod.rs b/compiler/rustc_codegen_ssa/src/mir/mod.rs
index 476ddbd9398..1cd400eecfb 100644
--- a/compiler/rustc_codegen_ssa/src/mir/mod.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/mod.rs
@@ -4,6 +4,7 @@ use rustc_middle::mir;
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, TyAndLayout};
 use rustc_middle::ty::{self, Instance, Ty, TypeFoldable};
+use rustc_symbol_mangling::typeid_for_fnabi;
 use rustc_target::abi::call::{FnAbi, PassMode};
 
 use std::iter;
@@ -244,6 +245,13 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     for (bb, _) in traversal::reverse_postorder(&mir) {
         fx.codegen_block(bb);
     }
+
+    // For backends that support CFI using type membership (i.e., testing whether a given  pointer
+    // is associated with a type identifier).
+    if cx.tcx().sess.is_sanitizer_cfi_enabled() {
+        let typeid = typeid_for_fnabi(cx.tcx(), fn_abi);
+        bx.type_metadata(llfn, typeid.clone());
+    }
 }
 
 /// Produces, for each argument, a `Value` pointing at the
diff --git a/compiler/rustc_codegen_ssa/src/traits/builder.rs b/compiler/rustc_codegen_ssa/src/traits/builder.rs
index e7da96f0ada..158e658301e 100644
--- a/compiler/rustc_codegen_ssa/src/traits/builder.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/builder.rs
@@ -158,6 +158,8 @@ pub trait BuilderMethods<'a, 'tcx>:
 
     fn range_metadata(&mut self, load: Self::Value, range: WrappingRange);
     fn nonnull_metadata(&mut self, load: Self::Value);
+    fn type_metadata(&mut self, function: Self::Function, typeid: String);
+    fn typeid_metadata(&mut self, typeid: String) -> Self::Value;
 
     fn store(&mut self, val: Self::Value, ptr: Self::Value, align: Align) -> Self::Value;
     fn store_with_flags(
diff --git a/compiler/rustc_codegen_ssa/src/traits/intrinsic.rs b/compiler/rustc_codegen_ssa/src/traits/intrinsic.rs
index 777436ad2ae..78bf22ef9f2 100644
--- a/compiler/rustc_codegen_ssa/src/traits/intrinsic.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/intrinsic.rs
@@ -24,6 +24,8 @@ pub trait IntrinsicCallMethods<'tcx>: BackendTypes {
     ///
     /// Currently has any effect only when LLVM versions prior to 12.0 are used as the backend.
     fn sideeffect(&mut self);
+    /// Trait method used to test whether a given pointer is associated with a type identifier.
+    fn type_test(&mut self, pointer: Self::Value, typeid: Self::Value) -> Self::Value;
     /// Trait method used to inject `va_start` on the "spoofed" `VaListImpl` in
     /// Rust defined C-variadic functions.
     fn va_start(&mut self, val: Self::Value) -> Self::Value;