--- /dev/null
+/* 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;
+ unsigned len;
+
+ 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;
+ }
+
+ /* It looks like the pkcs signature length in wrapper->length and the
+ * size obtained from the data dir entries, which lists the total size
+ * of certificate table, are both aligned to an octaword boundary, so
+ * we may have to deal with some padding.
+ */
+ ctx->sig_len = wrapper.length;
+ ctx->sig_offset += sizeof(wrapper);
+ ctx->sig_len -= sizeof(wrapper);
+ if (ctx->sig_len < 4) {
+ pr_debug("Signature data missing\n");
+ return -EKEYREJECTED;
+ }
+
+ /* What's left should be a PKCS#7 cert */
+ pkcs7 = pebuf + ctx->sig_offset;
+ if (pkcs7[0] != (ASN1_CONS_BIT | ASN1_SEQ))
+ goto not_pkcs7;
+
+ switch (pkcs7[1]) {
+ case 0 ... 0x7f:
+ len = pkcs7[1] + 2;
+ goto check_len;
+ case ASN1_INDEFINITE_LENGTH:
+ return 0;
+ case 0x81:
+ len = pkcs7[2] + 3;
+ goto check_len;
+ case 0x82:
+ len = ((pkcs7[2] << 8) | pkcs7[3]) + 4;
+ goto check_len;
+ case 0x83 ... 0xff:
+ return -EMSGSIZE;
+ default:
+ goto not_pkcs7;
+ }
+
+check_len:
+ if (len <= ctx->sig_len) {
+ /* There may be padding */
+ ctx->sig_len = len;
+ return 0;
+ }
+not_pkcs7:
+ 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;
+}
Code Review / kvmfornfv.git / blobdiff