pefile: Parse a PE binary to find a key and a signature contained therein
Parse a PE binary to find a key and a signature contained therein. Later
patches will check the signature and add the key if the signature checks out.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
diff --git a/crypto/asymmetric_keys/verify_pefile.c b/crypto/asymmetric_keys/verify_pefile.c
new file mode 100644
index 0000000..aec7c50
--- /dev/null
+++ b/crypto/asymmetric_keys/verify_pefile.c
@@ -0,0 +1,163 @@
+/* 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 <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;
+}
+
+/**
+ * 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;
+
+ return -ENOANO; // Not yet complete
+}