// SPDX-License-Identifier: GPL-2.0-or-later
/* Parse a signed PE binary
*
* Copyright (C) 2014 Red Hat, Inc. All Rights Reserved.
* Written by David Howells ([email protected])
*/
#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 <linux/verification.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 *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_warn("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_warn("Unsigned PE binary\n");
return -ENODATA;
}
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 = 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_warn("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);
/* sbsign rounds up the length of certificate table (in optional
* header data directories) to 8 byte alignment. However, the PE
* specification states that while entries are 8-byte aligned, this is
* not included in their length, and as a result, pesign has not
* rounded up since 0.110.
*/
if (wrapper.length > ctx->sig_len) {
pr_warn("Signature wrapper bigger than sig len (%x > %x)\n",
ctx->sig_len, wrapper.length);
return -ELIBBAD;
}
if (wrapper.revision != WIN_CERT_REVISION_2_0) {
pr_warn("Signature is not revision 2.0\n");
return -ENOTSUPP;
}
if (wrapper.cert_type != WIN_CERT_TYPE_PKCS_SIGNED_DATA) {
pr_warn("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_warn("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_warn("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(",%s", 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(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_warn("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;
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_warn("Digest mismatch\n");
ret = -EKEYREJECTED;
} else {
pr_debug("The digests match!\n");
}
error:
kfree_sensitive(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
* @trusted_keys: Signing certificate(s) to use as starting points
* @usage: The use to which the key is being put.
*
* 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:
*
* (*) -ENODATA if there is no signature present.
*
* (*) -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_keys,
enum key_being_used_for usage)
{
struct pefile_context ctx;
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;
ret = verify_pkcs7_signature(NULL, 0,
pebuf + ctx.sig_offset, ctx.sig_len,
trusted_keys, usage,
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);
error:
kfree_sensitive(ctx.digest);
return ret;
}
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