Add missing module flags for CFI and KCFI sanitizers

Set the cfi-normalize-integers and kcfi-offset module flags when
Control-Flow Integrity sanitizers are used, so functions generated by
the LLVM backend use the same CFI/KCFI options as rustc.

cfi-normalize-integers tells LLVM to also use integer normalization
for generated functions when -Zsanitizer-cfi-normalize-integers is
used.

kcfi-offset specifies the number of prefix nops between the KCFI
type hash and the function entry when -Z patchable-function-entry is
used. Note that LLVM assumes all indirectly callable functions use the
same number of prefix NOPs with -Zsanitizer=kcfi.

Author: samitolvanen

compiler/rustc_codegen_llvm/src/context.rs

@@ -11,6 +11,7 @@ use rustc_data_structures::base_n::{ToBaseN, ALPHANUMERIC_ONLY};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::small_c_str::SmallCStr;
 use rustc_hir::def_id::DefId;
+use rustc_middle::middle::codegen_fn_attrs::PatchableFunctionEntry;
 use rustc_middle::mir::mono::CodegenUnit;
 use rustc_middle::ty::layout::{
     FnAbiError, FnAbiOfHelpers, FnAbiRequest, HasParamEnv, LayoutError, LayoutOfHelpers,
@@ -226,6 +227,20 @@ pub unsafe fn create_module<'ll>(
         }
     }
 
+    // If we're normalizing integers with CFI, ensure LLVM generated functions do the same.
+    // See https://github.com/llvm/llvm-project/pull/104826
+    if sess.is_sanitizer_cfi_normalize_integers_enabled() {
+        let cfi_normalize_integers = c"cfi-normalize-integers".as_ptr().cast();
+        unsafe {
+            llvm::LLVMRustAddModuleFlagU32(
+                llmod,
+                llvm::LLVMModFlagBehavior::Override,
+                cfi_normalize_integers,
+                1,
+            );
+        }
+    }
+
     // Enable LTO unit splitting if specified or if CFI is enabled. (See https://reviews.llvm.org/D53891.)
     if sess.is_split_lto_unit_enabled() || sess.is_sanitizer_cfi_enabled() {
         let enable_split_lto_unit = c"EnableSplitLTOUnit".as_ptr();
@@ -245,6 +260,22 @@ pub unsafe fn create_module<'ll>(
         unsafe {
             llvm::LLVMRustAddModuleFlagU32(llmod, llvm::LLVMModFlagBehavior::Override, kcfi, 1);
         }
+
+        // Add "kcfi-offset" module flag with -Z patchable-function-entry (See
+        // https://reviews.llvm.org/D141172).
+        let pfe =
+            PatchableFunctionEntry::from_config(sess.opts.unstable_opts.patchable_function_entry);
+        if pfe.prefix() > 0 {
+            let kcfi_offset = c"kcfi-offset".as_ptr().cast();
+            unsafe {
+                llvm::LLVMRustAddModuleFlagU32(
+                    llmod,
+                    llvm::LLVMModFlagBehavior::Override,
+                    kcfi_offset,
+                    pfe.prefix().into(),
+                );
+            }
+        }
     }
 
     // Control Flow Guard is currently only supported by the MSVC linker on Windows.

tests/codegen/sanitizer/cfi/add-cfi-normalize-integers-flag.rs

@@ -0,0 +1,10 @@
+// Verifies that "cfi-normalize-integers" module flag is added.
+//
+//@ needs-sanitizer-cfi
+//@ compile-flags: -Clto -Ctarget-feature=-crt-static -Zsanitizer=cfi -Zsanitizer-cfi-normalize-integers
+
+#![crate_type = "lib"]
+
+pub fn foo() {}
+
+// CHECK: !{{[0-9]+}} = !{i32 4, !"cfi-normalize-integers", i32 1}

tests/codegen/sanitizer/kcfi/add-cfi-normalize-integers-flag.rs

@@ -0,0 +1,21 @@
+// Verifies that "cfi-normalize-integers" module flag is added.
+//
+//@ revisions: aarch64 x86_64
+//@ [aarch64] compile-flags: --target aarch64-unknown-none
+//@ [aarch64] needs-llvm-components: aarch64
+//@ [x86_64] compile-flags: --target x86_64-unknown-none
+//@ [x86_64] needs-llvm-components: x86
+//@ compile-flags: -Ctarget-feature=-crt-static -Zsanitizer=kcfi -Zsanitizer-cfi-normalize-integers
+
+#![feature(no_core, lang_items)]
+#![crate_type = "lib"]
+#![no_core]
+
+#[lang = "sized"]
+trait Sized {}
+#[lang = "copy"]
+trait Copy {}
+
+pub fn foo() {}
+
+// CHECK: !{{[0-9]+}} = !{i32 4, !"cfi-normalize-integers", i32 1}

tests/codegen/sanitizer/kcfi/add-kcfi-offset-flag.rs

@@ -0,0 +1,21 @@
+// Verifies that "kcfi-offset" module flag is added.
+//
+//@ revisions: aarch64 x86_64
+//@ [aarch64] compile-flags: --target aarch64-unknown-none
+//@ [aarch64] needs-llvm-components: aarch64
+//@ [x86_64] compile-flags: --target x86_64-unknown-none
+//@ [x86_64] needs-llvm-components: x86
+//@ compile-flags: -Ctarget-feature=-crt-static -Zsanitizer=kcfi -Z patchable-function-entry=4,3
+
+#![feature(no_core, lang_items, patchable_function_entry)]
+#![crate_type = "lib"]
+#![no_core]
+
+#[lang = "sized"]
+trait Sized {}
+#[lang = "copy"]
+trait Copy {}
+
+pub fn foo() {}
+
+// CHECK: !{{[0-9]+}} = !{i32 4, !"kcfi-offset", i32 3}