Auto merge of #112000 - wesleywiser:safestack, r=Amanieu

Add support for LLVM SafeStack

Adds support for LLVM [SafeStack] which provides backward edge control
flow protection by separating the stack into two parts: data which is
only accessed in provable safe ways is allocated on the normal stack
(the "safe stack") and all other data is placed in a separate allocation
(the "unsafe stack").

SafeStack support is enabled by passing `-Zsanitizer=safestack`.

[SafeStack]: https://clang.llvm.org/docs/SafeStack.html

cc `@rcvalle` #39699

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -88,6 +88,9 @@ pub fn sanitize_attrs<'ll>(
 
         attrs.push(llvm::AttributeKind::SanitizeMemTag.create_attr(cx.llcx));
     }
+    if enabled.contains(SanitizerSet::SAFESTACK) {
+        attrs.push(llvm::AttributeKind::SanitizeSafeStack.create_attr(cx.llcx));
+    }
     attrs
 }
 

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -196,6 +196,7 @@ pub enum AttributeKind {
     AllocSize = 37,
     AllocatedPointer = 38,
     AllocAlign = 39,
+    SanitizeSafeStack = 40,
 }
 
 /// LLVMIntPredicate

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -1188,6 +1188,9 @@ fn add_sanitizer_libraries(sess: &Session, crate_type: CrateType, linker: &mut d
     if sanitizer.contains(SanitizerSet::HWADDRESS) {
         link_sanitizer_runtime(sess, linker, "hwasan");
     }
+    if sanitizer.contains(SanitizerSet::SAFESTACK) {
+        link_sanitizer_runtime(sess, linker, "safestack");
+    }
 }
 
 fn link_sanitizer_runtime(sess: &Session, linker: &mut dyn Linker, name: &str) {

compiler/rustc_llvm/llvm-wrapper/LLVMWrapper.h

@@ -96,6 +96,7 @@ enum LLVMRustAttribute {
   AllocatedPointer = 38,
   AllocAlign = 39,
 #endif
+  SanitizeSafeStack = 40,
 };
 
 typedef struct OpaqueRustString *RustStringRef;

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -234,6 +234,8 @@ static Attribute::AttrKind fromRust(LLVMRustAttribute Kind) {
   case AllocAlign:
     return Attribute::AllocAlign;
 #endif
+  case SanitizeSafeStack:
+    return Attribute::SafeStack;
   }
   report_fatal_error("bad AttributeKind");
 }

compiler/rustc_session/src/options.rs

@@ -372,7 +372,7 @@ mod desc {
     pub const parse_opt_panic_strategy: &str = parse_panic_strategy;
     pub const parse_oom_strategy: &str = "either `panic` or `abort`";
     pub const parse_relro_level: &str = "one of: `full`, `partial`, or `off`";
-    pub const parse_sanitizers: &str = "comma separated list of sanitizers: `address`, `cfi`, `hwaddress`, `kcfi`, `kernel-address`, `leak`, `memory`, `memtag`, `shadow-call-stack`, or `thread`";
+    pub const parse_sanitizers: &str = "comma separated list of sanitizers: `address`, `cfi`, `hwaddress`, `kcfi`, `kernel-address`, `leak`, `memory`, `memtag`, `safestack`, `shadow-call-stack`, or `thread`";
     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`";
@@ -694,6 +694,7 @@ mod parse {
                     "shadow-call-stack" => SanitizerSet::SHADOWCALLSTACK,
                     "thread" => SanitizerSet::THREAD,
                     "hwaddress" => SanitizerSet::HWADDRESS,
+                    "safestack" => SanitizerSet::SAFESTACK,
                     _ => return false,
                 }
             }

compiler/rustc_target/src/spec/mod.rs

@@ -815,6 +815,7 @@ bitflags::bitflags! {
         const SHADOWCALLSTACK = 1 << 7;
         const KCFI    = 1 << 8;
         const KERNELADDRESS = 1 << 9;
+        const SAFESTACK = 1 << 10;
     }
 }
 
@@ -831,6 +832,7 @@ impl SanitizerSet {
             SanitizerSet::LEAK => "leak",
             SanitizerSet::MEMORY => "memory",
             SanitizerSet::MEMTAG => "memtag",
+            SanitizerSet::SAFESTACK => "safestack",
             SanitizerSet::SHADOWCALLSTACK => "shadow-call-stack",
             SanitizerSet::THREAD => "thread",
             SanitizerSet::HWADDRESS => "hwaddress",
@@ -871,6 +873,7 @@ impl IntoIterator for SanitizerSet {
             SanitizerSet::THREAD,
             SanitizerSet::HWADDRESS,
             SanitizerSet::KERNELADDRESS,
+            SanitizerSet::SAFESTACK,
         ]
         .iter()
         .copied()
@@ -2364,6 +2367,7 @@ impl Target {
                                 Some("leak") => SanitizerSet::LEAK,
                                 Some("memory") => SanitizerSet::MEMORY,
                                 Some("memtag") => SanitizerSet::MEMTAG,
+                                Some("safestack") => SanitizerSet::SAFESTACK,
                                 Some("shadow-call-stack") => SanitizerSet::SHADOWCALLSTACK,
                                 Some("thread") => SanitizerSet::THREAD,
                                 Some("hwaddress") => SanitizerSet::HWADDRESS,

compiler/rustc_target/src/spec/x86_64_unknown_linux_gnu.rs

@@ -11,6 +11,7 @@ pub fn target() -> Target {
         | SanitizerSet::CFI
         | SanitizerSet::LEAK
         | SanitizerSet::MEMORY
+        | SanitizerSet::SAFESTACK
         | SanitizerSet::THREAD;
     base.supports_xray = true;