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, 99 insertions, 0 deletions

diff --git a/security/landlock/errata.h b/security/landlock/errata.h
new file mode 100644
index 000000000..8e626acca
--- /dev/null
+++ b/security/landlock/errata.h
@@ -0,0 +1,99 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock - Errata information
+ *
+ * Copyright © 2025 Microsoft Corporation
+ */
+
+#ifndef _SECURITY_LANDLOCK_ERRATA_H
+#define _SECURITY_LANDLOCK_ERRATA_H
+
+#include <linux/init.h>
+
+struct landlock_erratum {
+	const int abi;
+	const u8 number;
+};
+
+/* clang-format off */
+#define LANDLOCK_ERRATUM(NUMBER) \
+	{ \
+		.abi = LANDLOCK_ERRATA_ABI, \
+		.number = NUMBER, \
+	},
+/* clang-format on */
+
+/*
+ * Some fixes may require user space to check if they are applied on the running
+ * kernel before using a specific feature.  For instance, this applies when a
+ * restriction was previously too restrictive and is now getting relaxed (for
+ * compatibility or semantic reasons).  However, non-visible changes for
+ * legitimate use (e.g. security fixes) do not require an erratum.
+ */
+static const struct landlock_erratum landlock_errata_init[] __initconst = {
+
+/*
+ * Only Sparse may not implement __has_include.  If a compiler does not
+ * implement __has_include, a warning will be printed at boot time (see
+ * setup.c).
+ */
+#ifdef __has_include
+
+#define LANDLOCK_ERRATA_ABI 1
+#if __has_include("errata/abi-1.h")
+#include "errata/abi-1.h"
+#endif
+#undef LANDLOCK_ERRATA_ABI
+
+#define LANDLOCK_ERRATA_ABI 2
+#if __has_include("errata/abi-2.h")
+#include "errata/abi-2.h"
+#endif
+#undef LANDLOCK_ERRATA_ABI
+
+#define LANDLOCK_ERRATA_ABI 3
+#if __has_include("errata/abi-3.h")
+#include "errata/abi-3.h"
+#endif
+#undef LANDLOCK_ERRATA_ABI
+
+#define LANDLOCK_ERRATA_ABI 4
+#if __has_include("errata/abi-4.h")
+#include "errata/abi-4.h"
+#endif
+#undef LANDLOCK_ERRATA_ABI
+
+#define LANDLOCK_ERRATA_ABI 5
+#if __has_include("errata/abi-5.h")
+#include "errata/abi-5.h"
+#endif
+#undef LANDLOCK_ERRATA_ABI
+
+#define LANDLOCK_ERRATA_ABI 6
+#if __has_include("errata/abi-6.h")
+#include "errata/abi-6.h"
+#endif
+#undef LANDLOCK_ERRATA_ABI
+
+/*
+ * For each new erratum, we need to include all the ABI files up to the impacted
+ * ABI to make all potential future intermediate errata easy to backport.
+ *
+ * If such change involves more than one ABI addition, then it must be in a
+ * dedicated commit with the same Fixes tag as used for the actual fix.
+ *
+ * Each commit creating a new security/landlock/errata/abi-*.h file must have a
+ * Depends-on tag to reference the commit that previously added the line to
+ * include this new file, except if the original Fixes tag is enough.
+ *
+ * Each erratum must be documented in its related ABI file, and a dedicated
+ * commit must update Documentation/userspace-api/landlock.rst to include this
+ * erratum.  This commit will not be backported.
+ */
+
+#endif
+
+	{}
+};
+
+#endif /* _SECURITY_LANDLOCK_ERRATA_H */