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, 102 insertions, 0 deletions

diff --git a/crypto/fips.c b/crypto/fips.c
new file mode 100644
index 000000000..c59711248
--- /dev/null
+++ b/crypto/fips.c
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * FIPS 200 support.
+ *
+ * Copyright (c) 2008 Neil Horman <nhorman@tuxdriver.com>
+ */
+
+#include <linux/export.h>
+#include <linux/fips.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/sysctl.h>
+#include <linux/notifier.h>
+#include <linux/string_choices.h>
+#include <generated/utsrelease.h>
+
+int fips_enabled;
+EXPORT_SYMBOL_GPL(fips_enabled);
+
+ATOMIC_NOTIFIER_HEAD(fips_fail_notif_chain);
+EXPORT_SYMBOL_GPL(fips_fail_notif_chain);
+
+/* Process kernel command-line parameter at boot time. fips=0 or fips=1 */
+static int __init fips_enable(char *str)
+{
+	if (kstrtoint(str, 0, &fips_enabled))
+		return 0;
+
+	fips_enabled = !!fips_enabled;
+	pr_info("fips mode: %s\n", str_enabled_disabled(fips_enabled));
+	return 1;
+}
+
+__setup("fips=", fips_enable);
+
+#define FIPS_MODULE_NAME CONFIG_CRYPTO_FIPS_NAME
+#ifdef CONFIG_CRYPTO_FIPS_CUSTOM_VERSION
+#define FIPS_MODULE_VERSION CONFIG_CRYPTO_FIPS_VERSION
+#else
+#define FIPS_MODULE_VERSION UTS_RELEASE
+#endif
+
+static char fips_name[] = FIPS_MODULE_NAME;
+static char fips_version[] = FIPS_MODULE_VERSION;
+
+static const struct ctl_table crypto_sysctl_table[] = {
+	{
+		.procname	= "fips_enabled",
+		.data		= &fips_enabled,
+		.maxlen		= sizeof(int),
+		.mode		= 0444,
+		.proc_handler	= proc_dointvec
+	},
+	{
+		.procname	= "fips_name",
+		.data		= &fips_name,
+		.maxlen		= 64,
+		.mode		= 0444,
+		.proc_handler	= proc_dostring
+	},
+	{
+		.procname	= "fips_version",
+		.data		= &fips_version,
+		.maxlen		= 64,
+		.mode		= 0444,
+		.proc_handler	= proc_dostring
+	},
+};
+
+static struct ctl_table_header *crypto_sysctls;
+
+static void crypto_proc_fips_init(void)
+{
+	crypto_sysctls = register_sysctl("crypto", crypto_sysctl_table);
+}
+
+static void crypto_proc_fips_exit(void)
+{
+	unregister_sysctl_table(crypto_sysctls);
+}
+
+void fips_fail_notify(void)
+{
+	if (fips_enabled)
+		atomic_notifier_call_chain(&fips_fail_notif_chain, 0, NULL);
+}
+EXPORT_SYMBOL_GPL(fips_fail_notify);
+
+static int __init fips_init(void)
+{
+	crypto_proc_fips_init();
+	return 0;
+}
+
+static void __exit fips_exit(void)
+{
+	crypto_proc_fips_exit();
+}
+
+module_init(fips_init);
+module_exit(fips_exit);