kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 69 insertions, 0 deletions

diff --git a/security/landlock/cred.c b/security/landlock/cred.c
new file mode 100644
index 000000000..cc419de75
--- /dev/null
+++ b/security/landlock/cred.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock - Credential hooks
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ * Copyright © 2024-2025 Microsoft Corporation
+ */
+
+#include <linux/binfmts.h>
+#include <linux/cred.h>
+#include <linux/lsm_hooks.h>
+
+#include "common.h"
+#include "cred.h"
+#include "ruleset.h"
+#include "setup.h"
+
+static void hook_cred_transfer(struct cred *const new,
+			       const struct cred *const old)
+{
+	const struct landlock_cred_security *const old_llcred =
+		landlock_cred(old);
+
+	landlock_get_ruleset(old_llcred->domain);
+	*landlock_cred(new) = *old_llcred;
+}
+
+static int hook_cred_prepare(struct cred *const new,
+			     const struct cred *const old, const gfp_t gfp)
+{
+	hook_cred_transfer(new, old);
+	return 0;
+}
+
+static void hook_cred_free(struct cred *const cred)
+{
+	struct landlock_ruleset *const dom = landlock_cred(cred)->domain;
+
+	if (dom)
+		landlock_put_ruleset_deferred(dom);
+}
+
+#ifdef CONFIG_AUDIT
+
+static int hook_bprm_creds_for_exec(struct linux_binprm *const bprm)
+{
+	/* Resets for each execution. */
+	landlock_cred(bprm->cred)->domain_exec = 0;
+	return 0;
+}
+
+#endif /* CONFIG_AUDIT */
+
+static struct security_hook_list landlock_hooks[] __ro_after_init = {
+	LSM_HOOK_INIT(cred_prepare, hook_cred_prepare),
+	LSM_HOOK_INIT(cred_transfer, hook_cred_transfer),
+	LSM_HOOK_INIT(cred_free, hook_cred_free),
+
+#ifdef CONFIG_AUDIT
+	LSM_HOOK_INIT(bprm_creds_for_exec, hook_bprm_creds_for_exec),
+#endif /* CONFIG_AUDIT */
+};
+
+__init void landlock_add_cred_hooks(void)
+{
+	security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
+			   &landlock_lsmid);
+}