1 files changed, 457 insertions, 0 deletions
diff --git a/crypto/asymmetric_keys/verify_pefile.c b/crypto/asymmetric_keys/verify_pefile.c
new file mode 100644
index 000000000000..79175e6ea0b2
--- /dev/null
+++ b/crypto/asymmetric_keys/verify_pefile.c
@@ -0,0 +1,457 @@
+/* Parse a signed PE binary
+ *
+ * Copyright (C) 2014 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#define pr_fmt(fmt) "PEFILE: "fmt
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/pe.h>
+#include <linux/asn1.h>
+#include <crypto/pkcs7.h>
+#include <crypto/hash.h>
+#include "verify_pefile.h"
+
+/*
+ * Parse a PE binary.
+ */
+static int pefile_parse_binary(const void *pebuf, unsigned int pelen,
+			       struct pefile_context *ctx)
+{
+	const struct mz_hdr *mz = pebuf;
+	const struct pe_hdr *pe;
+	const struct pe32_opt_hdr *pe32;
+	const struct pe32plus_opt_hdr *pe64;
+	const struct data_directory *ddir;
+	const struct data_dirent *dde;
+	const struct section_header *secs, *sec;
+	size_t cursor, datalen = pelen;
+
+	kenter("");
+
+#define chkaddr(base, x, s)						\
+	do {								\
+		if ((x) < base || (s) >= datalen || (x) > datalen - (s)) \
+			return -ELIBBAD;				\
+	} while (0)
+
+	chkaddr(0, 0, sizeof(*mz));
+	if (mz->magic != MZ_MAGIC)
+		return -ELIBBAD;
+	cursor = sizeof(*mz);
+
+	chkaddr(cursor, mz->peaddr, sizeof(*pe));
+	pe = pebuf + mz->peaddr;
+	if (pe->magic != PE_MAGIC)
+		return -ELIBBAD;
+	cursor = mz->peaddr + sizeof(*pe);
+
+	chkaddr(0, cursor, sizeof(pe32->magic));
+	pe32 = pebuf + cursor;
+	pe64 = pebuf + cursor;
+
+	switch (pe32->magic) {
+	case PE_OPT_MAGIC_PE32:
+		chkaddr(0, cursor, sizeof(*pe32));
+		ctx->image_checksum_offset =
+			(unsigned long)&pe32->csum - (unsigned long)pebuf;
+		ctx->header_size = pe32->header_size;
+		cursor += sizeof(*pe32);
+		ctx->n_data_dirents = pe32->data_dirs;
+		break;
+
+	case PE_OPT_MAGIC_PE32PLUS:
+		chkaddr(0, cursor, sizeof(*pe64));
+		ctx->image_checksum_offset =
+			(unsigned long)&pe64->csum - (unsigned long)pebuf;
+		ctx->header_size = pe64->header_size;
+		cursor += sizeof(*pe64);
+		ctx->n_data_dirents = pe64->data_dirs;
+		break;
+
+	default:
+		pr_debug("Unknown PEOPT magic = %04hx\n", pe32->magic);
+		return -ELIBBAD;
+	}
+
+	pr_debug("checksum @ %x\n", ctx->image_checksum_offset);
+	pr_debug("header size = %x\n", ctx->header_size);
+
+	if (cursor >= ctx->header_size || ctx->header_size >= datalen)
+		return -ELIBBAD;
+
+	if (ctx->n_data_dirents > (ctx->header_size - cursor) / sizeof(*dde))
+		return -ELIBBAD;
+
+	ddir = pebuf + cursor;
+	cursor += sizeof(*dde) * ctx->n_data_dirents;
+
+	ctx->cert_dirent_offset =
+		(unsigned long)&ddir->certs - (unsigned long)pebuf;
+	ctx->certs_size = ddir->certs.size;
+
+	if (!ddir->certs.virtual_address || !ddir->certs.size) {
+		pr_debug("Unsigned PE binary\n");
+		return -EKEYREJECTED;
+	}
+
+	chkaddr(ctx->header_size, ddir->certs.virtual_address,
+		ddir->certs.size);
+	ctx->sig_offset = ddir->certs.virtual_address;
+	ctx->sig_len = ddir->certs.size;
+	pr_debug("cert = %x @%x [%*ph]\n",
+		 ctx->sig_len, ctx->sig_offset,
+		 ctx->sig_len, pebuf + ctx->sig_offset);
+
+	ctx->n_sections = pe->sections;
+	if (ctx->n_sections > (ctx->header_size - cursor) / sizeof(*sec))
+		return -ELIBBAD;
+	ctx->secs = secs = pebuf + cursor;
+
+	return 0;
+}
+
+/*
+ * Check and strip the PE wrapper from around the signature and check that the
+ * remnant looks something like PKCS#7.
+ */
+static int pefile_strip_sig_wrapper(const void *pebuf,
+				    struct pefile_context *ctx)
+{
+	struct win_certificate wrapper;
+	const u8 *pkcs7;
+
+	if (ctx->sig_len < sizeof(wrapper)) {
+		pr_debug("Signature wrapper too short\n");
+		return -ELIBBAD;
+	}
+
+	memcpy(&wrapper, pebuf + ctx->sig_offset, sizeof(wrapper));
+	pr_debug("sig wrapper = { %x, %x, %x }\n",
+		 wrapper.length, wrapper.revision, wrapper.cert_type);
+
+	/* Both pesign and sbsign round up the length of certificate table
+	 * (in optional header data directories) to 8 byte alignment.
+	 */
+	if (round_up(wrapper.length, 8) != ctx->sig_len) {
+		pr_debug("Signature wrapper len wrong\n");
+		return -ELIBBAD;
+	}
+	if (wrapper.revision != WIN_CERT_REVISION_2_0) {
+		pr_debug("Signature is not revision 2.0\n");
+		return -ENOTSUPP;
+	}
+	if (wrapper.cert_type != WIN_CERT_TYPE_PKCS_SIGNED_DATA) {
+		pr_debug("Signature certificate type is not PKCS\n");
+		return -ENOTSUPP;
+	}
+
+	/* Looks like actual pkcs signature length is in wrapper->length.
+	 * size obtained from data dir entries lists the total size of
+	 * certificate table which is also aligned to octawrod boundary.
+	 *
+	 * So set signature length field appropriately.
+	 */
+	ctx->sig_len = wrapper.length;
+	ctx->sig_offset += sizeof(wrapper);
+	ctx->sig_len -= sizeof(wrapper);
+	if (ctx->sig_len == 0) {
+		pr_debug("Signature data missing\n");
+		return -EKEYREJECTED;
+	}
+
+	/* What's left should a PKCS#7 cert */
+	pkcs7 = pebuf + ctx->sig_offset;
+	if (pkcs7[0] == (ASN1_CONS_BIT | ASN1_SEQ)) {
+		if (pkcs7[1] == 0x82 &&
+		    pkcs7[2] == (((ctx->sig_len - 4) >> 8) & 0xff) &&
+		    pkcs7[3] ==  ((ctx->sig_len - 4)       & 0xff))
+			return 0;
+		if (pkcs7[1] == 0x80)
+			return 0;
+		if (pkcs7[1] > 0x82)
+			return -EMSGSIZE;
+	}
+
+	pr_debug("Signature data not PKCS#7\n");
+	return -ELIBBAD;
+}
+
+/*
+ * Compare two sections for canonicalisation.
+ */
+static int pefile_compare_shdrs(const void *a, const void *b)
+{
+	const struct section_header *shdra = a;
+	const struct section_header *shdrb = b;
+	int rc;
+
+	if (shdra->data_addr > shdrb->data_addr)
+		return 1;
+	if (shdrb->data_addr > shdra->data_addr)
+		return -1;
+
+	if (shdra->virtual_address > shdrb->virtual_address)
+		return 1;
+	if (shdrb->virtual_address > shdra->virtual_address)
+		return -1;
+
+	rc = strcmp(shdra->name, shdrb->name);
+	if (rc != 0)
+		return rc;
+
+	if (shdra->virtual_size > shdrb->virtual_size)
+		return 1;
+	if (shdrb->virtual_size > shdra->virtual_size)
+		return -1;
+
+	if (shdra->raw_data_size > shdrb->raw_data_size)
+		return 1;
+	if (shdrb->raw_data_size > shdra->raw_data_size)
+		return -1;
+
+	return 0;
+}
+
+/*
+ * Load the contents of the PE binary into the digest, leaving out the image
+ * checksum and the certificate data block.
+ */
+static int pefile_digest_pe_contents(const void *pebuf, unsigned int pelen,
+				     struct pefile_context *ctx,
+				     struct shash_desc *desc)
+{
+	unsigned *canon, tmp, loop, i, hashed_bytes;
+	int ret;
+
+	/* Digest the header and data directory, but leave out the image
+	 * checksum and the data dirent for the signature.
+	 */
+	ret = crypto_shash_update(desc, pebuf, ctx->image_checksum_offset);
+	if (ret < 0)
+		return ret;
+
+	tmp = ctx->image_checksum_offset + sizeof(uint32_t);
+	ret = crypto_shash_update(desc, pebuf + tmp,
+				  ctx->cert_dirent_offset - tmp);
+	if (ret < 0)
+		return ret;
+
+	tmp = ctx->cert_dirent_offset + sizeof(struct data_dirent);
+	ret = crypto_shash_update(desc, pebuf + tmp, ctx->header_size - tmp);
+	if (ret < 0)
+		return ret;
+
+	canon = kcalloc(ctx->n_sections, sizeof(unsigned), GFP_KERNEL);
+	if (!canon)
+		return -ENOMEM;
+
+	/* We have to canonicalise the section table, so we perform an
+	 * insertion sort.
+	 */
+	canon[0] = 0;
+	for (loop = 1; loop < ctx->n_sections; loop++) {
+		for (i = 0; i < loop; i++) {
+			if (pefile_compare_shdrs(&ctx->secs[canon[i]],
+						 &ctx->secs[loop]) > 0) {
+				memmove(&canon[i + 1], &canon[i],
+					(loop - i) * sizeof(canon[0]));
+				break;
+			}
+		}
+		canon[i] = loop;
+	}
+
+	hashed_bytes = ctx->header_size;
+	for (loop = 0; loop < ctx->n_sections; loop++) {
+		i = canon[loop];
+		if (ctx->secs[i].raw_data_size == 0)
+			continue;
+		ret = crypto_shash_update(desc,
+					  pebuf + ctx->secs[i].data_addr,
+					  ctx->secs[i].raw_data_size);
+		if (ret < 0) {
+			kfree(canon);
+			return ret;
+		}
+		hashed_bytes += ctx->secs[i].raw_data_size;
+	}
+	kfree(canon);
+
+	if (pelen > hashed_bytes) {
+		tmp = hashed_bytes + ctx->certs_size;
+		ret = crypto_shash_update(desc,
+					  pebuf + hashed_bytes,
+					  pelen - tmp);
+		if (ret < 0)
+			return ret;
+	}
+
+	return 0;
+}
+
+/*
+ * Digest the contents of the PE binary, leaving out the image checksum and the
+ * certificate data block.
+ */
+static int pefile_digest_pe(const void *pebuf, unsigned int pelen,
+			    struct pefile_context *ctx)
+{
+	struct crypto_shash *tfm;
+	struct shash_desc *desc;
+	size_t digest_size, desc_size;
+	void *digest;
+	int ret;
+
+	kenter(",%u", ctx->digest_algo);
+
+	/* Allocate the hashing algorithm we're going to need and find out how
+	 * big the hash operational data will be.
+	 */
+	tfm = crypto_alloc_shash(hash_algo_name[ctx->digest_algo], 0, 0);
+	if (IS_ERR(tfm))
+		return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
+
+	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
+	digest_size = crypto_shash_digestsize(tfm);
+
+	if (digest_size != ctx->digest_len) {
+		pr_debug("Digest size mismatch (%zx != %x)\n",
+			 digest_size, ctx->digest_len);
+		ret = -EBADMSG;
+		goto error_no_desc;
+	}
+	pr_debug("Digest: desc=%zu size=%zu\n", desc_size, digest_size);
+
+	ret = -ENOMEM;
+	desc = kzalloc(desc_size + digest_size, GFP_KERNEL);
+	if (!desc)
+		goto error_no_desc;
+
+	desc->tfm   = tfm;
+	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
+	ret = crypto_shash_init(desc);
+	if (ret < 0)
+		goto error;
+
+	ret = pefile_digest_pe_contents(pebuf, pelen, ctx, desc);
+	if (ret < 0)
+		goto error;
+
+	digest = (void *)desc + desc_size;
+	ret = crypto_shash_final(desc, digest);
+	if (ret < 0)
+		goto error;
+
+	pr_debug("Digest calc = [%*ph]\n", ctx->digest_len, digest);
+
+	/* Check that the PE file digest matches that in the MSCODE part of the
+	 * PKCS#7 certificate.
+	 */
+	if (memcmp(digest, ctx->digest, ctx->digest_len) != 0) {
+		pr_debug("Digest mismatch\n");
+		ret = -EKEYREJECTED;
+	} else {
+		pr_debug("The digests match!\n");
+	}
+
+error:
+	kfree(desc);
+error_no_desc:
+	crypto_free_shash(tfm);
+	kleave(" = %d", ret);
+	return ret;
+}
+
+/**
+ * verify_pefile_signature - Verify the signature on a PE binary image
+ * @pebuf: Buffer containing the PE binary image
+ * @pelen: Length of the binary image
+ * @trust_keyring: Signing certificates to use as starting points
+ * @_trusted: Set to true if trustworth, false otherwise
+ *
+ * Validate that the certificate chain inside the PKCS#7 message inside the PE
+ * binary image intersects keys we already know and trust.
+ *
+ * Returns, in order of descending priority:
+ *
+ *  (*) -ELIBBAD if the image cannot be parsed, or:
+ *
+ *  (*) -EKEYREJECTED if a signature failed to match for which we have a valid
+ *	key, or:
+ *
+ *  (*) 0 if at least one signature chain intersects with the keys in the trust
+ *	keyring, or:
+ *
+ *  (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
+ *	chain.
+ *
+ *  (*) -ENOKEY if we couldn't find a match for any of the signature chains in
+ *	the message.
+ *
+ * May also return -ENOMEM.
+ */
+int verify_pefile_signature(const void *pebuf, unsigned pelen,
+			    struct key *trusted_keyring, bool *_trusted)
+{
+	struct pkcs7_message *pkcs7;
+	struct pefile_context ctx;
+	const void *data;
+	size_t datalen;
+	int ret;
+
+	kenter("");
+
+	memset(&ctx, 0, sizeof(ctx));
+	ret = pefile_parse_binary(pebuf, pelen, &ctx);
+	if (ret < 0)
+		return ret;
+
+	ret = pefile_strip_sig_wrapper(pebuf, &ctx);
+	if (ret < 0)
+		return ret;
+
+	pkcs7 = pkcs7_parse_message(pebuf + ctx.sig_offset, ctx.sig_len);
+	if (IS_ERR(pkcs7))
+		return PTR_ERR(pkcs7);
+	ctx.pkcs7 = pkcs7;
+
+	ret = pkcs7_get_content_data(ctx.pkcs7, &data, &datalen, false);
+	if (ret < 0 || datalen == 0) {
+		pr_devel("PKCS#7 message does not contain data\n");
+		ret = -EBADMSG;
+		goto error;
+	}
+
+	ret = mscode_parse(&ctx);
+	if (ret < 0)
+		goto error;
+
+	pr_debug("Digest: %u [%*ph]\n",
+		 ctx.digest_len, ctx.digest_len, ctx.digest);
+
+	/* Generate the digest and check against the PKCS7 certificate
+	 * contents.
+	 */
+	ret = pefile_digest_pe(pebuf, pelen, &ctx);
+	if (ret < 0)
+		goto error;
+
+	ret = pkcs7_verify(pkcs7);
+	if (ret < 0)
+		goto error;
+
+	ret = pkcs7_validate_trust(pkcs7, trusted_keyring, _trusted);
+
+error:
+	pkcs7_free_message(ctx.pkcs7);
+	return ret;
+}