/* 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;
}
/**
* 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 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;
return -ENOANO; // Not yet complete
}
