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, 94 insertions, 0 deletions

diff --git a/net/mac80211/aes_gmac.c b/net/mac80211/aes_gmac.c
new file mode 100644
index 000000000..811a83d8d
--- /dev/null
+++ b/net/mac80211/aes_gmac.c
@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * AES-GMAC for IEEE 802.11 BIP-GMAC-128 and BIP-GMAC-256
+ * Copyright 2015, Qualcomm Atheros, Inc.
+ */
+
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/err.h>
+#include <crypto/aead.h>
+#include <crypto/aes.h>
+
+#include <net/mac80211.h>
+#include "key.h"
+#include "aes_gmac.h"
+
+int ieee80211_aes_gmac(struct crypto_aead *tfm, const u8 *aad, u8 *nonce,
+		       const u8 *data, size_t data_len, u8 *mic)
+{
+	struct scatterlist sg[5];
+	u8 *zero, *__aad, iv[AES_BLOCK_SIZE];
+	struct aead_request *aead_req;
+	int reqsize = sizeof(*aead_req) + crypto_aead_reqsize(tfm);
+	const __le16 *fc;
+	int ret;
+
+	if (data_len < IEEE80211_GMAC_MIC_LEN)
+		return -EINVAL;
+
+	aead_req = kzalloc(reqsize + IEEE80211_GMAC_MIC_LEN + GMAC_AAD_LEN,
+			   GFP_ATOMIC);
+	if (!aead_req)
+		return -ENOMEM;
+
+	zero = (u8 *)aead_req + reqsize;
+	__aad = zero + IEEE80211_GMAC_MIC_LEN;
+	memcpy(__aad, aad, GMAC_AAD_LEN);
+
+	fc = (const __le16 *)aad;
+	if (ieee80211_is_beacon(*fc)) {
+		/* mask Timestamp field to zero */
+		sg_init_table(sg, 5);
+		sg_set_buf(&sg[0], __aad, GMAC_AAD_LEN);
+		sg_set_buf(&sg[1], zero, 8);
+		sg_set_buf(&sg[2], data + 8,
+			   data_len - 8 - IEEE80211_GMAC_MIC_LEN);
+		sg_set_buf(&sg[3], zero, IEEE80211_GMAC_MIC_LEN);
+		sg_set_buf(&sg[4], mic, IEEE80211_GMAC_MIC_LEN);
+	} else {
+		sg_init_table(sg, 4);
+		sg_set_buf(&sg[0], __aad, GMAC_AAD_LEN);
+		sg_set_buf(&sg[1], data, data_len - IEEE80211_GMAC_MIC_LEN);
+		sg_set_buf(&sg[2], zero, IEEE80211_GMAC_MIC_LEN);
+		sg_set_buf(&sg[3], mic, IEEE80211_GMAC_MIC_LEN);
+	}
+
+	memcpy(iv, nonce, GMAC_NONCE_LEN);
+	memset(iv + GMAC_NONCE_LEN, 0, sizeof(iv) - GMAC_NONCE_LEN);
+	iv[AES_BLOCK_SIZE - 1] = 0x01;
+
+	aead_request_set_tfm(aead_req, tfm);
+	aead_request_set_crypt(aead_req, sg, sg, 0, iv);
+	aead_request_set_ad(aead_req, GMAC_AAD_LEN + data_len);
+
+	ret = crypto_aead_encrypt(aead_req);
+	kfree_sensitive(aead_req);
+
+	return ret;
+}
+
+struct crypto_aead *ieee80211_aes_gmac_key_setup(const u8 key[],
+						 size_t key_len)
+{
+	struct crypto_aead *tfm;
+	int err;
+
+	tfm = crypto_alloc_aead("gcm(aes)", 0, CRYPTO_ALG_ASYNC);
+	if (IS_ERR(tfm))
+		return tfm;
+
+	err = crypto_aead_setkey(tfm, key, key_len);
+	if (!err)
+		err = crypto_aead_setauthsize(tfm, IEEE80211_GMAC_MIC_LEN);
+	if (!err)
+		return tfm;
+
+	crypto_free_aead(tfm);
+	return ERR_PTR(err);
+}
+
+void ieee80211_aes_gmac_key_free(struct crypto_aead *tfm)
+{
+	crypto_free_aead(tfm);
+}