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, 293 insertions, 0 deletions

diff --git a/crypto/ecrdsa.c b/crypto/ecrdsa.c
new file mode 100644
index 000000000..93c9e7d76
--- /dev/null
+++ b/crypto/ecrdsa.c
@@ -0,0 +1,293 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Elliptic Curve (Russian) Digital Signature Algorithm for Cryptographic API
+ *
+ * Copyright (c) 2019 Vitaly Chikunov <vt@altlinux.org>
+ *
+ * References:
+ * GOST 34.10-2018, GOST R 34.10-2012, RFC 7091, ISO/IEC 14888-3:2018.
+ *
+ * Historical references:
+ * GOST R 34.10-2001, RFC 4357, ISO/IEC 14888-3:2006/Amd 1:2010.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ */
+
+#include <linux/module.h>
+#include <linux/crypto.h>
+#include <crypto/sig.h>
+#include <crypto/streebog.h>
+#include <crypto/internal/ecc.h>
+#include <crypto/internal/sig.h>
+#include <linux/oid_registry.h>
+#include "ecrdsa_params.asn1.h"
+#include "ecrdsa_pub_key.asn1.h"
+#include "ecrdsa_defs.h"
+
+#define ECRDSA_MAX_SIG_SIZE (2 * 512 / 8)
+#define ECRDSA_MAX_DIGITS (512 / 64)
+
+struct ecrdsa_ctx {
+	enum OID algo_oid; /* overall public key oid */
+	enum OID curve_oid; /* parameter */
+	enum OID digest_oid; /* parameter */
+	const struct ecc_curve *curve; /* curve from oid */
+	unsigned int digest_len; /* parameter (bytes) */
+	const char *digest; /* digest name from oid */
+	unsigned int key_len; /* @key length (bytes) */
+	const char *key; /* raw public key */
+	struct ecc_point pub_key;
+	u64 _pubp[2][ECRDSA_MAX_DIGITS]; /* point storage for @pub_key */
+};
+
+static const struct ecc_curve *get_curve_by_oid(enum OID oid)
+{
+	switch (oid) {
+	case OID_gostCPSignA:
+	case OID_gostTC26Sign256B:
+		return &gost_cp256a;
+	case OID_gostCPSignB:
+	case OID_gostTC26Sign256C:
+		return &gost_cp256b;
+	case OID_gostCPSignC:
+	case OID_gostTC26Sign256D:
+		return &gost_cp256c;
+	case OID_gostTC26Sign512A:
+		return &gost_tc512a;
+	case OID_gostTC26Sign512B:
+		return &gost_tc512b;
+	/* The following two aren't implemented: */
+	case OID_gostTC26Sign256A:
+	case OID_gostTC26Sign512C:
+	default:
+		return NULL;
+	}
+}
+
+static int ecrdsa_verify(struct crypto_sig *tfm,
+			 const void *src, unsigned int slen,
+			 const void *digest, unsigned int dlen)
+{
+	struct ecrdsa_ctx *ctx = crypto_sig_ctx(tfm);
+	unsigned int ndigits = dlen / sizeof(u64);
+	u64 r[ECRDSA_MAX_DIGITS]; /* witness (r) */
+	u64 _r[ECRDSA_MAX_DIGITS]; /* -r */
+	u64 s[ECRDSA_MAX_DIGITS]; /* second part of sig (s) */
+	u64 e[ECRDSA_MAX_DIGITS]; /* h \mod q */
+	u64 *v = e;		  /* e^{-1} \mod q */
+	u64 z1[ECRDSA_MAX_DIGITS];
+	u64 *z2 = _r;
+	struct ecc_point cc = ECC_POINT_INIT(s, e, ndigits); /* reuse s, e */
+
+	/*
+	 * Digest value, digest algorithm, and curve (modulus) should have the
+	 * same length (256 or 512 bits), public key and signature should be
+	 * twice bigger.
+	 */
+	if (!ctx->curve ||
+	    !ctx->digest ||
+	    !src ||
+	    !digest ||
+	    !ctx->pub_key.x ||
+	    dlen != ctx->digest_len ||
+	    dlen != ctx->curve->g.ndigits * sizeof(u64) ||
+	    ctx->pub_key.ndigits != ctx->curve->g.ndigits ||
+	    dlen * 2 != slen ||
+	    WARN_ON(slen > ECRDSA_MAX_SIG_SIZE) ||
+	    WARN_ON(dlen > STREEBOG512_DIGEST_SIZE))
+		return -EBADMSG;
+
+	vli_from_be64(s, src, ndigits);
+	vli_from_be64(r, src + ndigits * sizeof(u64), ndigits);
+
+	/* Step 1: verify that 0 < r < q, 0 < s < q */
+	if (vli_is_zero(r, ndigits) ||
+	    vli_cmp(r, ctx->curve->n, ndigits) >= 0 ||
+	    vli_is_zero(s, ndigits) ||
+	    vli_cmp(s, ctx->curve->n, ndigits) >= 0)
+		return -EKEYREJECTED;
+
+	/* Step 2: calculate hash (h) of the message (passed as input) */
+	/* Step 3: calculate e = h \mod q */
+	vli_from_le64(e, digest, ndigits);
+	if (vli_cmp(e, ctx->curve->n, ndigits) >= 0)
+		vli_sub(e, e, ctx->curve->n, ndigits);
+	if (vli_is_zero(e, ndigits))
+		e[0] = 1;
+
+	/* Step 4: calculate v = e^{-1} \mod q */
+	vli_mod_inv(v, e, ctx->curve->n, ndigits);
+
+	/* Step 5: calculate z_1 = sv \mod q, z_2 = -rv \mod q */
+	vli_mod_mult_slow(z1, s, v, ctx->curve->n, ndigits);
+	vli_sub(_r, ctx->curve->n, r, ndigits);
+	vli_mod_mult_slow(z2, _r, v, ctx->curve->n, ndigits);
+
+	/* Step 6: calculate point C = z_1P + z_2Q, and R = x_c \mod q */
+	ecc_point_mult_shamir(&cc, z1, &ctx->curve->g, z2, &ctx->pub_key,
+			      ctx->curve);
+	if (vli_cmp(cc.x, ctx->curve->n, ndigits) >= 0)
+		vli_sub(cc.x, cc.x, ctx->curve->n, ndigits);
+
+	/* Step 7: if R == r signature is valid */
+	if (!vli_cmp(cc.x, r, ndigits))
+		return 0;
+	else
+		return -EKEYREJECTED;
+}
+
+int ecrdsa_param_curve(void *context, size_t hdrlen, unsigned char tag,
+		       const void *value, size_t vlen)
+{
+	struct ecrdsa_ctx *ctx = context;
+
+	ctx->curve_oid = look_up_OID(value, vlen);
+	if (ctx->curve_oid == OID__NR)
+		return -EINVAL;
+	ctx->curve = get_curve_by_oid(ctx->curve_oid);
+	return 0;
+}
+
+/* Optional. If present should match expected digest algo OID. */
+int ecrdsa_param_digest(void *context, size_t hdrlen, unsigned char tag,
+			const void *value, size_t vlen)
+{
+	struct ecrdsa_ctx *ctx = context;
+	int digest_oid = look_up_OID(value, vlen);
+
+	if (digest_oid != ctx->digest_oid)
+		return -EINVAL;
+	return 0;
+}
+
+int ecrdsa_parse_pub_key(void *context, size_t hdrlen, unsigned char tag,
+			 const void *value, size_t vlen)
+{
+	struct ecrdsa_ctx *ctx = context;
+
+	ctx->key = value;
+	ctx->key_len = vlen;
+	return 0;
+}
+
+static u8 *ecrdsa_unpack_u32(u32 *dst, void *src)
+{
+	memcpy(dst, src, sizeof(u32));
+	return src + sizeof(u32);
+}
+
+/* Parse BER encoded subjectPublicKey. */
+static int ecrdsa_set_pub_key(struct crypto_sig *tfm, const void *key,
+			      unsigned int keylen)
+{
+	struct ecrdsa_ctx *ctx = crypto_sig_ctx(tfm);
+	unsigned int ndigits;
+	u32 algo, paramlen;
+	u8 *params;
+	int err;
+
+	err = asn1_ber_decoder(&ecrdsa_pub_key_decoder, ctx, key, keylen);
+	if (err < 0)
+		return err;
+
+	/* Key parameters is in the key after keylen. */
+	params = ecrdsa_unpack_u32(&paramlen,
+			  ecrdsa_unpack_u32(&algo, (u8 *)key + keylen));
+
+	if (algo == OID_gost2012PKey256) {
+		ctx->digest	= "streebog256";
+		ctx->digest_oid	= OID_gost2012Digest256;
+		ctx->digest_len	= 256 / 8;
+	} else if (algo == OID_gost2012PKey512) {
+		ctx->digest	= "streebog512";
+		ctx->digest_oid	= OID_gost2012Digest512;
+		ctx->digest_len	= 512 / 8;
+	} else
+		return -ENOPKG;
+	ctx->algo_oid = algo;
+
+	/* Parse SubjectPublicKeyInfo.AlgorithmIdentifier.parameters. */
+	err = asn1_ber_decoder(&ecrdsa_params_decoder, ctx, params, paramlen);
+	if (err < 0)
+		return err;
+	/*
+	 * Sizes of algo (set in digest_len) and curve should match
+	 * each other.
+	 */
+	if (!ctx->curve ||
+	    ctx->curve->g.ndigits * sizeof(u64) != ctx->digest_len)
+		return -ENOPKG;
+	/*
+	 * Key is two 256- or 512-bit coordinates which should match
+	 * curve size.
+	 */
+	if ((ctx->key_len != (2 * 256 / 8) &&
+	     ctx->key_len != (2 * 512 / 8)) ||
+	    ctx->key_len != ctx->curve->g.ndigits * sizeof(u64) * 2)
+		return -ENOPKG;
+
+	ndigits = ctx->key_len / sizeof(u64) / 2;
+	ctx->pub_key = ECC_POINT_INIT(ctx->_pubp[0], ctx->_pubp[1], ndigits);
+	vli_from_le64(ctx->pub_key.x, ctx->key, ndigits);
+	vli_from_le64(ctx->pub_key.y, ctx->key + ndigits * sizeof(u64),
+		      ndigits);
+
+	if (ecc_is_pubkey_valid_partial(ctx->curve, &ctx->pub_key))
+		return -EKEYREJECTED;
+
+	return 0;
+}
+
+static unsigned int ecrdsa_key_size(struct crypto_sig *tfm)
+{
+	struct ecrdsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	/*
+	 * Verify doesn't need any output, so it's just informational
+	 * for keyctl to determine the key bit size.
+	 */
+	return ctx->pub_key.ndigits * sizeof(u64) * BITS_PER_BYTE;
+}
+
+static unsigned int ecrdsa_max_size(struct crypto_sig *tfm)
+{
+	struct ecrdsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	return 2 * ctx->pub_key.ndigits * sizeof(u64);
+}
+
+static struct sig_alg ecrdsa_alg = {
+	.verify		= ecrdsa_verify,
+	.set_pub_key	= ecrdsa_set_pub_key,
+	.key_size	= ecrdsa_key_size,
+	.max_size	= ecrdsa_max_size,
+	.base = {
+		.cra_name	 = "ecrdsa",
+		.cra_driver_name = "ecrdsa-generic",
+		.cra_priority	 = 100,
+		.cra_module	 = THIS_MODULE,
+		.cra_ctxsize	 = sizeof(struct ecrdsa_ctx),
+	},
+};
+
+static int __init ecrdsa_mod_init(void)
+{
+	return crypto_register_sig(&ecrdsa_alg);
+}
+
+static void __exit ecrdsa_mod_fini(void)
+{
+	crypto_unregister_sig(&ecrdsa_alg);
+}
+
+module_init(ecrdsa_mod_init);
+module_exit(ecrdsa_mod_fini);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Vitaly Chikunov <vt@altlinux.org>");
+MODULE_DESCRIPTION("EC-RDSA generic algorithm");
+MODULE_ALIAS_CRYPTO("ecrdsa");
+MODULE_ALIAS_CRYPTO("ecrdsa-generic");