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Add missing module flags for CFI and KCFI sanitizers

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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.
This commit is contained in:
Sami Tolvanen 2024-08-16 20:33:58 +00:00
parent 6b678c57b6
commit 40f1d9d154
4 changed files with 83 additions and 0 deletions
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31
compiler/rustc_codegen_llvm/src/context.rs
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@ -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.