[PATCH v4 3/7] lib: crypto: import pkcs7_verify.c from linux

AKASHI Takahiro
2020-07-17T07:16:26Z

The file, pkcs7_verify.c, will now be imported from linux code
(crypto/asymmetric_keys/pkcs7_verify.c)
and modified to fit into U-Boot environment.

In particular, pkcs7_verify_one() function will be used in a later patch
to rework signature verification logic aiming to support intermediate
certificates in "chain of trust."

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
---
lib/crypto/Kconfig | 3 +
lib/crypto/Makefile | 1 +
lib/crypto/pkcs7_verify.c | 521 ++++++++++++++++++++++++++++++++++++++
3 files changed, 525 insertions(+)
create mode 100644 lib/crypto/pkcs7_verify.c

diff --git a/lib/crypto/Kconfig b/lib/crypto/Kconfig
index 2b221b915aa6..6369bafac07b 100644
--- a/lib/crypto/Kconfig
+++ b/lib/crypto/Kconfig
@@ -49,4 +49,7 @@ config PKCS7_MESSAGE_PARSER
This option provides support for parsing PKCS#7 format messages for
signature data and provides the ability to verify the signature.

+config PKCS7_VERIFY
+ bool
+
endif # ASYMMETRIC_KEY_TYPE
diff --git a/lib/crypto/Makefile b/lib/crypto/Makefile
index 8267fee0a7b8..f3a414525d2a 100644
--- a/lib/crypto/Makefile
+++ b/lib/crypto/Makefile
@@ -44,6 +44,7 @@ obj-$(CONFIG_PKCS7_MESSAGE_PARSER) += pkcs7_message.o
pkcs7_message-y := \
pkcs7.asn1.o \
pkcs7_parser.o
+obj-$(CONFIG_PKCS7_VERIFY) += pkcs7_verify.o

$(obj)/pkcs7_parser.o: $(obj)/pkcs7.asn1.h
$(obj)/pkcs7.asn1.o: $(obj)/pkcs7.asn1.c $(obj)/pkcs7.asn1.h
diff --git a/lib/crypto/pkcs7_verify.c b/lib/crypto/pkcs7_verify.c
new file mode 100644
index 000000000000..a893fa3b586b
--- /dev/null
+++ b/lib/crypto/pkcs7_verify.c
@@ -0,0 +1,521 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Verify the signature on a PKCS#7 message.
+ *
+ * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells at redhat.com)
+ */
+
+#define pr_fmt(fmt) "PKCS7: "fmt
+#ifdef __UBOOT__
+#include <string.h>
+#include <linux/bitops.h>
+#include <linux/compat.h>
+#include <linux/asn1.h>
+#include <crypto/public_key.h>
+#include <crypto/pkcs7_parser.h>
+#else
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/asn1.h>
+#include <crypto/hash.h>
+#include <crypto/hash_info.h>
+#include <crypto/public_key.h>
+#include "pkcs7_parser.h"
+#endif
+
+/*
+ * Digest the relevant parts of the PKCS#7 data
+ */
+#ifdef __UBOOT__
+static int pkcs7_digest(struct pkcs7_message *pkcs7,
+ struct pkcs7_signed_info *sinfo)
+{
+ return 0;
+}
+#else
+static int pkcs7_digest(struct pkcs7_message *pkcs7,
+ struct pkcs7_signed_info *sinfo)
+{
+ struct public_key_signature *sig = sinfo->sig;
+ struct crypto_shash *tfm;
+ struct shash_desc *desc;
+ size_t desc_size;
+ int ret;
+
+ kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);
+
+ /* The digest was calculated already. */
+ if (sig->digest)
+ return 0;
+
+ if (!sinfo->sig->hash_algo)
+ return -ENOPKG;
+
+ /* Allocate the hashing algorithm we're going to need and find out how
+ * big the hash operational data will be.
+ */
+ tfm = crypto_alloc_shash(sinfo->sig->hash_algo, 0, 0);
+ if (IS_ERR(tfm))
+ return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
+
+ desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
+ sig->digest_size = crypto_shash_digestsize(tfm);
+
+ ret = -ENOMEM;
+ sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
+ if (!sig->digest)
+ goto error_no_desc;
+
+ desc = kzalloc(desc_size, GFP_KERNEL);
+ if (!desc)
+ goto error_no_desc;
+
+ desc->tfm = tfm;
+
+ /* Digest the message [RFC2315 9.3] */
+ ret = crypto_shash_digest(desc, pkcs7->data, pkcs7->data_len,
+ sig->digest);
+ if (ret < 0)
+ goto error;
+ pr_devel("MsgDigest = [%*ph]\n", 8, sig->digest);
+
+ /* However, if there are authenticated attributes, there must be a
+ * message digest attribute amongst them which corresponds to the
+ * digest we just calculated.
+ */
+ if (sinfo->authattrs) {
+ u8 tag;
+
+ if (!sinfo->msgdigest) {
+ pr_warn("Sig %u: No messageDigest\n", sinfo->index);
+ ret = -EKEYREJECTED;
+ goto error;
+ }
+
+ if (sinfo->msgdigest_len != sig->digest_size) {
+ pr_debug("Sig %u: Invalid digest size (%u)\n",
+ sinfo->index, sinfo->msgdigest_len);
+ ret = -EBADMSG;
+ goto error;
+ }
+
+ if (memcmp(sig->digest, sinfo->msgdigest,
+ sinfo->msgdigest_len) != 0) {
+ pr_debug("Sig %u: Message digest doesn't match\n",
+ sinfo->index);
+ ret = -EKEYREJECTED;
+ goto error;
+ }
+
+ /* We then calculate anew, using the authenticated attributes
+ * as the contents of the digest instead. Note that we need to
+ * convert the attributes from a CONT.0 into a SET before we
+ * hash it.
+ */
+ memset(sig->digest, 0, sig->digest_size);
+
+ ret = crypto_shash_init(desc);
+ if (ret < 0)
+ goto error;
+ tag = ASN1_CONS_BIT | ASN1_SET;
+ ret = crypto_shash_update(desc, &tag, 1);
+ if (ret < 0)
+ goto error;
+ ret = crypto_shash_finup(desc, sinfo->authattrs,
+ sinfo->authattrs_len, sig->digest);
+ if (ret < 0)
+ goto error;
+ pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
+ }
+
+error:
+ kfree(desc);
+error_no_desc:
+ crypto_free_shash(tfm);
+ kleave(" = %d", ret);
+ return ret;
+}
+
+int pkcs7_get_digest(struct pkcs7_message *pkcs7, const u8 **buf, u32 *len,
+ enum hash_algo *hash_algo)
+{
+ struct pkcs7_signed_info *sinfo = pkcs7->signed_infos;
+ int i, ret;
+
+ /*
+ * This function doesn't support messages with more than one signature.
+ */
+ if (sinfo == NULL || sinfo->next != NULL)
+ return -EBADMSG;
+
+ ret = pkcs7_digest(pkcs7, sinfo);
+ if (ret)
+ return ret;
+
+ *buf = sinfo->sig->digest;
+ *len = sinfo->sig->digest_size;
+
+ for (i = 0; i < HASH_ALGO__LAST; i++)
+ if (!strcmp(hash_algo_name[i], sinfo->sig->hash_algo)) {
+ *hash_algo = i;
+ break;
+ }
+
+ return 0;
+}
+#endif /* !__UBOOT__ */
+
+/*
+ * Find the key (X.509 certificate) to use to verify a PKCS#7 message. PKCS#7
+ * uses the issuer's name and the issuing certificate serial number for
+ * matching purposes. These must match the certificate issuer's name (not
+ * subject's name) and the certificate serial number [RFC 2315 6.7].
+ */
+static int pkcs7_find_key(struct pkcs7_message *pkcs7,
+ struct pkcs7_signed_info *sinfo)
+{
+ struct x509_certificate *x509;
+ unsigned certix = 1;
+
+ kenter("%u", sinfo->index);
+
+ for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
+ /* I'm _assuming_ that the generator of the PKCS#7 message will
+ * encode the fields from the X.509 cert in the same way in the
+ * PKCS#7 message - but I can't be 100% sure of that. It's
+ * possible this will need element-by-element comparison.
+ */
+ if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
+ continue;
+ pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
+ sinfo->index, certix);
+
+ if (strcmp(x509->pub->pkey_algo, sinfo->sig->pkey_algo) != 0) {
+ pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
+ sinfo->index);
+ continue;
+ }
+
+ sinfo->signer = x509;
+ return 0;
+ }
+
+ /* The relevant X.509 cert isn't found here, but it might be found in
+ * the trust keyring.
+ */
+ pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
+ sinfo->index,
+ sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
+ return 0;
+}
+
+/*
+ * Verify the internal certificate chain as best we can.
+ */
+static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
+ struct pkcs7_signed_info *sinfo)
+{
+ struct public_key_signature *sig;
+ struct x509_certificate *x509 = sinfo->signer, *p;
+ struct asymmetric_key_id *auth;
+ int ret;
+
+ kenter("");
+
+ for (p = pkcs7->certs; p; p = p->next)
+ p->seen = false;
+
+ for (;;) {
+ pr_debug("verify %s: %*phN\n",
+ x509->subject,
+ x509->raw_serial_size, x509->raw_serial);
+ x509->seen = true;
+
+ if (x509->blacklisted) {
+ /* If this cert is blacklisted, then mark everything
+ * that depends on this as blacklisted too.
+ */
+ sinfo->blacklisted = true;
+ for (p = sinfo->signer; p != x509; p = p->signer)
+ p->blacklisted = true;
+ pr_debug("- blacklisted\n");
+ return 0;
+ }
+
+ if (x509->unsupported_key)
+ goto unsupported_crypto_in_x509;
+
+ pr_debug("- issuer %s\n", x509->issuer);
+ sig = x509->sig;
+ if (sig->auth_ids[0])
+ pr_debug("- authkeyid.id %*phN\n",
+ sig->auth_ids[0]->len, sig->auth_ids[0]->data);
+ if (sig->auth_ids[1])
+ pr_debug("- authkeyid.skid %*phN\n",
+ sig->auth_ids[1]->len, sig->auth_ids[1]->data);
+
+ if (x509->self_signed) {
+ /* If there's no authority certificate specified, then
+ * the certificate must be self-signed and is the root
+ * of the chain. Likewise if the cert is its own
+ * authority.
+ */
+ if (x509->unsupported_sig)
+ goto unsupported_crypto_in_x509;
+ x509->signer = x509;
+ pr_debug("- self-signed\n");
+ return 0;
+ }
+
+ /* Look through the X.509 certificates in the PKCS#7 message's
+ * list to see if the next one is there.
+ */
+ auth = sig->auth_ids[0];
+ if (auth) {
+ pr_debug("- want %*phN\n", auth->len, auth->data);
+ for (p = pkcs7->certs; p; p = p->next) {
+ pr_debug("- cmp [%u] %*phN\n",
+ p->index, p->id->len, p->id->data);
+ if (asymmetric_key_id_same(p->id, auth))
+ goto found_issuer_check_skid;
+ }
+ } else if (sig->auth_ids[1]) {
+ auth = sig->auth_ids[1];
+ pr_debug("- want %*phN\n", auth->len, auth->data);
+ for (p = pkcs7->certs; p; p = p->next) {
+ if (!p->skid)
+ continue;
+ pr_debug("- cmp [%u] %*phN\n",
+ p->index, p->skid->len, p->skid->data);
+ if (asymmetric_key_id_same(p->skid, auth))
+ goto found_issuer;
+ }
+ }
+
+ /* We didn't find the root of this chain */
+ pr_debug("- top\n");
+ return 0;
+
+ found_issuer_check_skid:
+ /* We matched issuer + serialNumber, but if there's an
+ * authKeyId.keyId, that must match the CA subjKeyId also.
+ */
+ if (sig->auth_ids[1] &&
+ !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
+ pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
+ sinfo->index, x509->index, p->index);
+ return -EKEYREJECTED;
+ }
+ found_issuer:
+ pr_debug("- subject %s\n", p->subject);
+ if (p->seen) {
+ pr_warn("Sig %u: X.509 chain contains loop\n",
+ sinfo->index);
+ return 0;
+ }
+ ret = public_key_verify_signature(p->pub, x509->sig);
+ if (ret < 0)
+ return ret;
+ x509->signer = p;
+ if (x509 == p) {
+ pr_debug("- self-signed\n");
+ return 0;
+ }
+ x509 = p;
+#ifndef __UBOOT__
+ might_sleep();
+#endif
+ }
+
+unsupported_crypto_in_x509:
+ /* Just prune the certificate chain at this point if we lack some
+ * crypto module to go further. Note, however, we don't want to set
+ * sinfo->unsupported_crypto as the signed info block may still be
+ * validatable against an X.509 cert lower in the chain that we have a
+ * trusted copy of.
+ */
+ return 0;
+}
+
+/*
+ * Verify one signed information block from a PKCS#7 message.
+ */
+#ifndef __UBOOT__
+static
+#endif
+int pkcs7_verify_one(struct pkcs7_message *pkcs7,
+ struct pkcs7_signed_info *sinfo)
+{
+ int ret;
+
+ kenter(",%u", sinfo->index);
+
+ /* First of all, digest the data in the PKCS#7 message and the
+ * signed information block
+ */
+ ret = pkcs7_digest(pkcs7, sinfo);
+ if (ret < 0)
+ return ret;
+
+ /* Find the key for the signature if there is one */
+ ret = pkcs7_find_key(pkcs7, sinfo);
+ if (ret < 0)
+ return ret;
+
+ if (!sinfo->signer)
+ return 0;
+
+ pr_devel("Using X.509[%u] for sig %u\n",
+ sinfo->signer->index, sinfo->index);
+
+ /* Check that the PKCS#7 signing time is valid according to the X.509
+ * certificate. We can't, however, check against the system clock
+ * since that may not have been set yet and may be wrong.
+ */
+ if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
+ if (sinfo->signing_time < sinfo->signer->valid_from ||
+ sinfo->signing_time > sinfo->signer->valid_to) {
+ pr_warn("Message signed outside of X.509 validity window\n");
+ return -EKEYREJECTED;
+ }
+ }
+
+ /* Verify the PKCS#7 binary against the key */
+ ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
+ if (ret < 0)
+ return ret;
+
+ pr_devel("Verified signature %u\n", sinfo->index);
+
+ /* Verify the internal certificate chain */
+ return pkcs7_verify_sig_chain(pkcs7, sinfo);
+}
+
+#ifndef __UBOOT__
+/**
+ * pkcs7_verify - Verify a PKCS#7 message
+ * @pkcs7: The PKCS#7 message to be verified
+ * @usage: The use to which the key is being put
+ *
+ * Verify a PKCS#7 message is internally consistent - that is, the data digest
+ * matches the digest in the AuthAttrs and any signature in the message or one
+ * of the X.509 certificates it carries that matches another X.509 cert in the
+ * message can be verified.
+ *
+ * This does not look to match the contents of the PKCS#7 message against any
+ * external public keys.
+ *
+ * Returns, in order of descending priority:
+ *
+ * (*) -EKEYREJECTED if a key was selected that had a usage restriction at
+ * odds with the specified usage, or:
+ *
+ * (*) -EKEYREJECTED if a signature failed to match for which we found an
+ * appropriate X.509 certificate, or:
+ *
+ * (*) -EBADMSG if some part of the message was invalid, or:
+ *
+ * (*) 0 if a signature chain passed verification, or:
+ *
+ * (*) -EKEYREJECTED if a blacklisted key was encountered, or:
+ *
+ * (*) -ENOPKG if none of the signature chains are verifiable because suitable
+ * crypto modules couldn't be found.
+ */
+int pkcs7_verify(struct pkcs7_message *pkcs7,
+ enum key_being_used_for usage)
+{
+ struct pkcs7_signed_info *sinfo;
+ int actual_ret = -ENOPKG;
+ int ret;
+
+ kenter("");
+
+ switch (usage) {
+ case VERIFYING_MODULE_SIGNATURE:
+ if (pkcs7->data_type != OID_data) {
+ pr_warn("Invalid module sig (not pkcs7-data)\n");
+ return -EKEYREJECTED;
+ }
+ if (pkcs7->have_authattrs) {
+ pr_warn("Invalid module sig (has authattrs)\n");
+ return -EKEYREJECTED;
+ }
+ break;
+ case VERIFYING_FIRMWARE_SIGNATURE:
+ if (pkcs7->data_type != OID_data) {
+ pr_warn("Invalid firmware sig (not pkcs7-data)\n");
+ return -EKEYREJECTED;
+ }
+ if (!pkcs7->have_authattrs) {
+ pr_warn("Invalid firmware sig (missing authattrs)\n");
+ return -EKEYREJECTED;
+ }
+ break;
+ case VERIFYING_KEXEC_PE_SIGNATURE:
+ if (pkcs7->data_type != OID_msIndirectData) {
+ pr_warn("Invalid kexec sig (not Authenticode)\n");
+ return -EKEYREJECTED;
+ }
+ /* Authattr presence checked in parser */
+ break;
+ case VERIFYING_UNSPECIFIED_SIGNATURE:
+ if (pkcs7->data_type != OID_data) {
+ pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
+ return -EKEYREJECTED;
+ }
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
+ ret = pkcs7_verify_one(pkcs7, sinfo);
+ if (sinfo->blacklisted) {
+ if (actual_ret == -ENOPKG)
+ actual_ret = -EKEYREJECTED;
+ continue;
+ }
+ if (ret < 0) {
+ if (ret == -ENOPKG) {
+ sinfo->unsupported_crypto = true;
+ continue;
+ }
+ kleave(" = %d", ret);
+ return ret;
+ }
+ actual_ret = 0;
+ }
+
+ kleave(" = %d", actual_ret);
+ return actual_ret;
+}
+EXPORT_SYMBOL_GPL(pkcs7_verify);
+
+/**
+ * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
+ * @pkcs7: The PKCS#7 message
+ * @data: The data to be verified
+ * @datalen: The amount of data
+ *
+ * Supply the detached data needed to verify a PKCS#7 message. Note that no
+ * attempt to retain/pin the data is made. That is left to the caller. The
+ * data will not be modified by pkcs7_verify() and will not be freed when the
+ * PKCS#7 message is freed.
+ *
+ * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
+ */
+int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
+ const void *data, size_t datalen)
+{
+ if (pkcs7->data) {
+ pr_debug("Data already supplied\n");
+ return -EINVAL;
+ }
+ pkcs7->data = data;
+ pkcs7->data_len = datalen;
+ return 0;
+}
+#endif /* __UBOOT__ */
--
2.27.0