[PATCH 2/4] x86/rust: support SLS

[Miguel Ojeda]

Support the `SLS` speculation mitigation by enabling the target features
that Clang does.

Without this, `objtool` would complain if enabled for individual object
files (like it is planned in the future), e.g.

    rust/core.o: warning: objtool:
    _R...next_up+0x44: missing int3 after ret

Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
---
 scripts/generate_rust_target.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/scripts/generate_rust_target.rs b/scripts/generate_rust_target.rs
index 163089ae13ba..7e374369afca 100644
--- a/scripts/generate_rust_target.rs
+++ b/scripts/generate_rust_target.rs
@@ -165,6 +165,14 @@ fn main() {
             features += ",+retpoline-indirect-branches";
             features += ",+retpoline-indirect-calls";
         }
+        if cfg.has("SLS") {
+            // The kernel uses `-mharden-sls=all`, which Clang maps to both these target features in
+            // `clang/lib/Driver/ToolChains/Arch/X86.cpp`. These should be eventually enabled via
+            // `-Ctarget-feature` when `rustc` starts recognizing them (or via a new dedicated
+            // flag); see https://github.com/rust-lang/rust/issues/116851.
+            features += ",+harden-sls-ijmp";
+            features += ",+harden-sls-ret";
+        }
         ts.push("features", features);
         ts.push("llvm-target", "x86_64-linux-gnu");
         ts.push("target-pointer-width", "64");
-- 
2.42.0