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, 42 insertions, 0 deletions

diff --git a/security/landlock/limits.h b/security/landlock/limits.h
new file mode 100644
index 000000000..08d5f2f6d
--- /dev/null
+++ b/security/landlock/limits.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock - Limits for different components
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ * Copyright © 2021-2025 Microsoft Corporation
+ */
+
+#ifndef _SECURITY_LANDLOCK_LIMITS_H
+#define _SECURITY_LANDLOCK_LIMITS_H
+
+#include <linux/bitops.h>
+#include <linux/limits.h>
+#include <uapi/linux/landlock.h>
+
+/* clang-format off */
+
+#define LANDLOCK_MAX_NUM_LAYERS		16
+#define LANDLOCK_MAX_NUM_RULES		U32_MAX
+
+#define LANDLOCK_LAST_ACCESS_FS		LANDLOCK_ACCESS_FS_RESOLVE_UNIX
+#define LANDLOCK_MASK_ACCESS_FS		((LANDLOCK_LAST_ACCESS_FS << 1) - 1)
+#define LANDLOCK_NUM_ACCESS_FS		__const_hweight64(LANDLOCK_MASK_ACCESS_FS)
+
+#define LANDLOCK_LAST_ACCESS_NET	LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP
+#define LANDLOCK_MASK_ACCESS_NET	((LANDLOCK_LAST_ACCESS_NET << 1) - 1)
+#define LANDLOCK_NUM_ACCESS_NET		__const_hweight64(LANDLOCK_MASK_ACCESS_NET)
+
+#define LANDLOCK_LAST_SCOPE		LANDLOCK_SCOPE_SIGNAL
+#define LANDLOCK_MASK_SCOPE		((LANDLOCK_LAST_SCOPE << 1) - 1)
+#define LANDLOCK_NUM_SCOPE		__const_hweight64(LANDLOCK_MASK_SCOPE)
+
+#define LANDLOCK_NUM_ACCESS_MAX \
+	MAX(MAX(LANDLOCK_NUM_ACCESS_FS, LANDLOCK_NUM_ACCESS_NET), LANDLOCK_NUM_SCOPE)
+
+#define LANDLOCK_LAST_RESTRICT_SELF	LANDLOCK_RESTRICT_SELF_TSYNC
+#define LANDLOCK_MASK_RESTRICT_SELF	((LANDLOCK_LAST_RESTRICT_SELF << 1) - 1)
+
+/* clang-format on */
+
+#endif /* _SECURITY_LANDLOCK_LIMITS_H */