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>

4 files changed, 217 insertions, 0 deletions

diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
index 14cac2860afa..ca41be5631c7 100644
--- a/crypto/asymmetric_keys/Kconfig
+++ b/crypto/asymmetric_keys/Kconfig
@@ -59,4 +59,13 @@ config PKCS7_TEST_KEY
 
           This is intended for testing the PKCS#7 parser.
 
+config SIGNED_PE_FILE_VERIFICATION
+        bool "Support for PE file signature verification"
+        depends on PKCS7_MESSAGE_PARSER=y
+        select ASN1
+        select OID_REGISTRY
+        help
+          This option provides support for verifying the signature(s) on a
+          signed PE binary.
+
 endif # ASYMMETRIC_KEY_TYPE
diff --git a/crypto/asymmetric_keys/Makefile b/crypto/asymmetric_keys/Makefile
index 92d0e9af24d5..3e4de5297015 100644
--- a/crypto/asymmetric_keys/Makefile
+++ b/crypto/asymmetric_keys/Makefile
@@ -47,3 +47,11 @@ clean-files	+= pkcs7-asn1.c pkcs7-asn1.h
 obj-$(CONFIG_PKCS7_TEST_KEY) += pkcs7_test_key.o
 pkcs7_test_key-y := \
         pkcs7_key_type.o
+
+#
+# Signed PE binary-wrapped key handling
+#
+obj-$(CONFIG_SIGNED_PE_FILE_VERIFICATION) += verify_signed_pefile.o
+
+verify_signed_pefile-y := \
+        verify_pefile.o
diff --git a/crypto/asymmetric_keys/verify_pefile.c b/crypto/asymmetric_keys/verify_pefile.c
new file mode 100644
index 000000000000..aec7c509404e
--- /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
+}
diff --git a/crypto/asymmetric_keys/verify_pefile.h b/crypto/asymmetric_keys/verify_pefile.h
new file mode 100644
index 000000000000..e165d23458d4
--- /dev/null
+++ b/crypto/asymmetric_keys/verify_pefile.h
@@ -0,0 +1,37 @@
+/* PE Binary parser bits
+ *
+ * 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.
+ */
+
+#include <linux/verify_pefile.h>
+#include <crypto/pkcs7.h>
+#include <crypto/hash_info.h>
+
+struct pefile_context {
+        unsigned        header_size;
+        unsigned        image_checksum_offset;
+        unsigned        cert_dirent_offset;
+        unsigned        n_data_dirents;
+        unsigned        n_sections;
+        unsigned        certs_size;
+        unsigned        sig_offset;
+        unsigned        sig_len;
+        const struct section_header *secs;
+        struct pkcs7_message *pkcs7;
+
+        /* PKCS#7 MS Individual Code Signing content */
+        const void      *digest;                /* Digest */
+        unsigned        digest_len;             /* Digest length */
+        enum hash_algo  digest_algo;            /* Digest algorithm */
+};
+
+#define kenter(FMT, ...)                                        \
+        pr_devel("==> %s("FMT")\n", __func__, ##__VA_ARGS__)
+#define kleave(FMT, ...) \
+        pr_devel("<== %s()"FMT"\n", __func__, ##__VA_ARGS__)