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, 61 insertions, 0 deletions

diff --git a/security/apparmor/crypto.c b/security/apparmor/crypto.c
new file mode 100644
index 000000000..d8a7bde94
--- /dev/null
+++ b/security/apparmor/crypto.c
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * AppArmor security module
+ *
+ * This file contains AppArmor policy loading interface function definitions.
+ *
+ * Copyright 2013 Canonical Ltd.
+ *
+ * Fns to provide a checksum of policy that has been loaded this can be
+ * compared to userspace policy compiles to check loaded policy is what
+ * it should be.
+ */
+
+#include <crypto/sha2.h>
+
+#include "include/apparmor.h"
+#include "include/crypto.h"
+
+unsigned int aa_hash_size(void)
+{
+	return SHA256_DIGEST_SIZE;
+}
+
+char *aa_calc_hash(void *data, size_t len)
+{
+	char *hash;
+
+	hash = kzalloc(SHA256_DIGEST_SIZE, GFP_KERNEL);
+	if (!hash)
+		return ERR_PTR(-ENOMEM);
+
+	sha256(data, len, hash);
+	return hash;
+}
+
+int aa_calc_profile_hash(struct aa_profile *profile, u32 version, void *start,
+			 size_t len)
+{
+	struct sha256_ctx sctx;
+	__le32 le32_version = cpu_to_le32(version);
+
+	if (!aa_g_hash_policy)
+		return 0;
+
+	profile->hash = kzalloc(SHA256_DIGEST_SIZE, GFP_KERNEL);
+	if (!profile->hash)
+		return -ENOMEM;
+
+	sha256_init(&sctx);
+	sha256_update(&sctx, (u8 *)&le32_version, 4);
+	sha256_update(&sctx, (u8 *)start, len);
+	sha256_final(&sctx, profile->hash);
+	return 0;
+}
+
+int __init init_profile_hash(void)
+{
+	if (apparmor_initialized)
+		aa_info_message("AppArmor sha256 policy hashing enabled");
+	return 0;
+}