Add support for control-flow protection

This change adds a flag for configuring control-flow protection in the
LLVM backend. In Clang, this flag is exposed as `-fcf-protection` with
options `none|branch|return|full`. This convention is followed for
`rustc`, though as a codegen option: `rustc -Z
cf-protection=<none|branch|return|full>`.

Co-authored-by: BlackHoleFox <blackholefoxdev@gmail.com>

2 files changed, 43 insertions, 4 deletions

diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 79962d5db89..68e7cc3dc98 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -63,6 +63,22 @@ pub enum CFGuard {
     Checks,
 }
 
+/// The different settings that the `-Z cf-protection` flag can have.
+#[derive(Clone, Copy, PartialEq, Hash, Debug)]
+pub enum CFProtection {
+    /// Do not enable control-flow protection
+    None,
+
+    /// Emit control-flow protection for branches (enables indirect branch tracking).
+    Branch,
+
+    /// Emit control-flow protection for returns.
+    Return,
+
+    /// Emit control-flow protection for both branches and returns.
+    Full,
+}
+
 #[derive(Clone, Copy, Debug, PartialEq, Hash)]
 pub enum OptLevel {
     No,         // -O0
@@ -2630,11 +2646,11 @@ impl PpMode {
 /// we have an opt-in scheme here, so one is hopefully forced to think about
 /// how the hash should be calculated when adding a new command-line argument.
 crate mod dep_tracking {
-    use super::LdImpl;
     use super::{
-        BranchProtection, CFGuard, CrateType, DebugInfo, ErrorOutputType, InstrumentCoverage,
-        LinkerPluginLto, LocationDetail, LtoCli, OptLevel, OutputType, OutputTypes, Passes,
-        SourceFileHashAlgorithm, SwitchWithOptPath, SymbolManglingVersion, TrimmedDefPaths,
+        BranchProtection, CFGuard, CFProtection, CrateType, DebugInfo, ErrorOutputType,
+        InstrumentCoverage, LdImpl, LinkerPluginLto, LocationDetail, LtoCli, OptLevel, OutputType,
+        OutputTypes, Passes, SourceFileHashAlgorithm, SwitchWithOptPath, SymbolManglingVersion,
+        TrimmedDefPaths,
     };
     use crate::lint;
     use crate::options::WasiExecModel;
@@ -2715,6 +2731,7 @@ crate mod dep_tracking {
         NativeLibKind,
         SanitizerSet,
         CFGuard,
+        CFProtection,
         TargetTriple,
         Edition,
         LinkerPluginLto,
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index ae1b638c344..c069144fa9f 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -380,6 +380,7 @@ mod desc {
     pub const parse_sanitizer_memory_track_origins: &str = "0, 1, or 2";
     pub const parse_cfguard: &str =
         "either a boolean (`yes`, `no`, `on`, `off`, etc), `checks`, or `nochecks`";
+    pub const parse_cfprotection: &str = "`none`|`no`|`n` (default), `branch`, `return`, or `full`|`yes`|`y` (equivalent to `branch` and `return`)";
     pub const parse_strip: &str = "either `none`, `debuginfo`, or `symbols`";
     pub const parse_linker_flavor: &str = ::rustc_target::spec::LinkerFlavor::one_of();
     pub const parse_optimization_fuel: &str = "crate=integer";
@@ -695,6 +696,25 @@ mod parse {
         true
     }
 
+    crate fn parse_cfprotection(slot: &mut CFProtection, v: Option<&str>) -> bool {
+        if v.is_some() {
+            let mut bool_arg = None;
+            if parse_opt_bool(&mut bool_arg, v) {
+                *slot = if bool_arg.unwrap() { CFProtection::Full } else { CFProtection::None };
+                return true;
+            }
+        }
+
+        *slot = match v {
+            None | Some("none") => CFProtection::None,
+            Some("branch") => CFProtection::Branch,
+            Some("return") => CFProtection::Return,
+            Some("full") => CFProtection::Full,
+            Some(_) => return false,
+        };
+        true
+    }
+
     crate fn parse_linker_flavor(slot: &mut Option<LinkerFlavor>, v: Option<&str>) -> bool {
         match v.and_then(LinkerFlavor::from_str) {
             Some(lf) => *slot = Some(lf),
@@ -1142,6 +1162,8 @@ options! {
         "select which borrowck is used (`mir` or `migrate`) (default: `migrate`)"),
     branch_protection: BranchProtection = (BranchProtection::default(), parse_branch_protection, [TRACKED],
         "set options for branch target identification and pointer authentication on AArch64"),
+    cf_protection: CFProtection = (CFProtection::None, parse_cfprotection, [TRACKED],
+        "instrument control-flow architecture protection"),
     cgu_partitioning_strategy: Option<String> = (None, parse_opt_string, [TRACKED],
         "the codegen unit partitioning strategy to use"),
     chalk: bool = (false, parse_bool, [TRACKED],