Add SafeStack support to rustc

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

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;
 

src/bootstrap/llvm.rs

@@ -1017,7 +1017,7 @@ fn supported_sanitizers(
         "x86_64-unknown-illumos" => common_libs("illumos", "x86_64", &["asan"]),
         "x86_64-pc-solaris" => common_libs("solaris", "x86_64", &["asan"]),
         "x86_64-unknown-linux-gnu" => {
-            common_libs("linux", "x86_64", &["asan", "lsan", "msan", "tsan"])
+            common_libs("linux", "x86_64", &["asan", "lsan", "msan", "safestack", "tsan"])
         }
         "x86_64-unknown-linux-musl" => {
             common_libs("linux", "x86_64", &["asan", "lsan", "msan", "tsan"])

src/doc/rustc/src/exploit-mitigations.md

@@ -66,7 +66,7 @@ equivalent.
 | Heap corruption protection | Yes | 1.32.0 (2019-01-17) (via operating system default or specified allocator) |
 | Stack smashing protection | Yes | Nightly |
 | Forward-edge control flow protection | Yes | Nightly |
-| Backward-edge control flow protection (e.g., shadow and safe stack) | No | |
+| Backward-edge control flow protection (e.g., shadow and safe stack) | Yes | Nightly |
 
 <small id="fn:1">1\. See
 <https://github.com/rust-lang/rust/tree/master/compiler/rustc_target/src/spec>
@@ -443,20 +443,21 @@ Newer processors provide hardware assistance for backward-edge control flow
 protection, such as ARM Pointer Authentication, and Intel Shadow Stack as
 part of Intel CET.
 
-The Rust compiler does not support shadow or safe stack. There is work
-currently ongoing to add support for the sanitizers[40], which may or may
-not include support for safe stack<sup id="fnref:7" role="doc-noteref"><a
-href="#fn:7" class="footnote">7</a></sup>.
+The Rust compiler supports shadow stack for aarch64 only
+<sup id="fnref:7" role="doc-noteref"><a href="#fn:7" class="footnote">7</a></sup>
+on nightly Rust compilers [43]-[44]. Safe stack is available on nightly
+Rust compilers [45]-[46].
 
 ```text
 $ readelf -s target/release/hello-rust | grep __safestack_init
+  1177: 00000000000057b0   444 FUNC    GLOBAL DEFAULT    9 __safestack_init
 ```
 Fig. 16. Checking if LLVM SafeStack is enabled for a given binary.
 
 The presence of the `__safestack_init` symbol indicates that LLVM SafeStack
-is enabled for a given binary. Conversely, the absence of the
+is enabled for a given binary (see Fig. 16). Conversely, the absence of the
 `__safestack_init` symbol indicates that LLVM SafeStack is not enabled for a
-given binary (see Fig. 16).
+given binary.
 
 <small id="fn:7">7\. The shadow stack implementation for the AMD64
 architecture and equivalent in LLVM was removed due to performance and
@@ -628,3 +629,15 @@ defaults (unrelated to `READ_IMPLIES_EXEC`).
 
 42. bbjornse. “add codegen option for using LLVM stack smash protection #84197.”
     GitHub. <https://github.com/rust-lang/rust/pull/84197>
+
+43. ivanloz. “Add support for LLVM ShadowCallStack. #98208.” GitHub.
+    <https://github.com/rust-lang/rust/pull/98208>.
+
+44. “ShadowCallStack.” The Rust Unstable Book.
+    [https://doc.rust-lang.org/unstable-book/compiler-flags/sanitizer.html#shadowcallstack](../unstable-book/compiler-flags/sanitizer.html#shadowcallstack).
+
+45. W. Wiser. “Add support for LLVM SafeStack #112000” GitHub.
+    <https://github.com/rust-lang/rust/pull/112000>
+
+46. “SafeStack.” The Rust Unstable Book.
+    [https://doc.rust-lang/org/unstable-book/compiler-flags/sanitizer.html#safestack](../unstable-book/compiler-flags/sanitizer.html#safestack).

src/doc/unstable-book/src/compiler-flags/sanitizer.md

@@ -21,7 +21,8 @@ This feature allows for use of one of following sanitizers:
 * [MemorySanitizer](#memorysanitizer) a detector of uninitialized reads.
 * [MemTagSanitizer](#memtagsanitizer) fast memory error detector based on
   Armv8.5-A Memory Tagging Extension.
-* [ShadowCallStack](#shadowcallstack) provides backward-edge control flow protection.
+* [SafeStack](#safestack) provides backward-edge control flow protection by separating the stack into safe and unsafe regions.
+* [ShadowCallStack](#shadowcallstack) provides backward-edge control flow protection (aarch64 only).
 * [ThreadSanitizer](#threadsanitizer) a fast data race detector.
 
 To enable a sanitizer compile with `-Zsanitizer=address`,`-Zsanitizer=cfi`,
@@ -712,6 +713,16 @@ To enable this target feature compile with `-C target-feature="+mte"`.
 
 See the [LLVM MemTagSanitizer documentation][llvm-memtag] for more details.
 
+# SafeStack
+
+SafeStack provides backward edge control flow protection by separating the stack into data which is only accessed safely (the safe stack) and all other data (the unsafe stack).
+
+SafeStack can be enabled with the `-Zsanitizer=safestack` option and is supported on the following targets:
+
+* `x86_64-unknown-linux-gnu`
+
+See the [Clang SafeStack documentation][clang-safestack] for more details.
+
 # ShadowCallStack
 
 ShadowCallStack provides backward edge control flow protection by storing a function's return address in a separately allocated 'shadow call stack' and loading the return address from that shadow call stack.
@@ -828,6 +839,7 @@ Sanitizers produce symbolized stacktraces when llvm-symbolizer binary is in `PAT
 [clang-kcfi]: https://clang.llvm.org/docs/ControlFlowIntegrity.html#fsanitize-kcfi
 [clang-lsan]: https://clang.llvm.org/docs/LeakSanitizer.html
 [clang-msan]: https://clang.llvm.org/docs/MemorySanitizer.html
+[clang-safestack]: https://clang.llvm.org/docs/SafeStack.html
 [clang-scs]: https://clang.llvm.org/docs/ShadowCallStack.html
 [clang-tsan]: https://clang.llvm.org/docs/ThreadSanitizer.html
 [linux-kasan]: https://www.kernel.org/doc/html/latest/dev-tools/kasan.html

src/tools/compiletest/src/header/needs.rs

@@ -70,6 +70,11 @@ pub(super) fn handle_needs(
             condition: cache.sanitizer_shadow_call_stack,
             ignore_reason: "ignored on targets without shadow call stacks",
         },
+        Need {
+            name: "needs-sanitizer-safestack",
+            condition: cache.sanitizer_safestack,
+            ignore_reason: "ignored on targets without SafeStack support",
+        },
         Need {
             name: "needs-run-enabled",
             condition: config.run_enabled(),
@@ -184,6 +189,7 @@ pub(super) struct CachedNeedsConditions {
     sanitizer_hwaddress: bool,
     sanitizer_memtag: bool,
     sanitizer_shadow_call_stack: bool,
+    sanitizer_safestack: bool,
     xray: bool,
     rust_lld: bool,
     i686_dlltool: bool,
@@ -220,6 +226,7 @@ impl CachedNeedsConditions {
             sanitizer_hwaddress: util::HWASAN_SUPPORTED_TARGETS.contains(target),
             sanitizer_memtag: util::MEMTAG_SUPPORTED_TARGETS.contains(target),
             sanitizer_shadow_call_stack: util::SHADOWCALLSTACK_SUPPORTED_TARGETS.contains(target),
+            sanitizer_safestack: util::SAFESTACK_SUPPORTED_TARGETS.contains(target),
             xray: util::XRAY_SUPPORTED_TARGETS.contains(target),
 
             // For tests using the `needs-rust-lld` directive (e.g. for `-Zgcc-ld=lld`), we need to find

src/tools/compiletest/src/util.rs

@@ -104,6 +104,8 @@ pub const XRAY_SUPPORTED_TARGETS: &[&str] = &[
     "x86_64-unknown-openbsd",
 ];
 
+pub const SAFESTACK_SUPPORTED_TARGETS: &[&str] = &["x86_64-unknown-linux-gnu"];
+
 pub fn make_new_path(path: &str) -> String {
     assert!(cfg!(windows));
     // Windows just uses PATH as the library search path, so we have to

tests/codegen/sanitizer-safestack-attr-check.rs

@@ -0,0 +1,11 @@
+// This tests that the safestack attribute is applied when enabling the safe-stack sanitizer.
+//
+// needs-sanitizer-safestack
+// compile-flags: -Zsanitizer=safestack
+
+#![crate_type = "lib"]
+
+// CHECK: ; Function Attrs:{{.*}}safestack
+pub fn tagged() {}
+
+// CHECK: attributes #0 = {{.*}}safestack