crypto: asymmetric_keys - add KUnit tests for the PE parser

Add self-contained KUnit tests for pefile_parse_binary(), exercised
through verify_pefile_signature() -- which parses the image before any
signature check, so no keyring or real signature is needed. The cases
build small malformed PE images in memory:

  - a PE declaring 0 data-directory entries: the certificate table entry
    at fixed index 4 is absent and must be rejected (-ELIBBAD), not read
    out of bounds;
  - a PE declaring 5 entries with a zero (unsigned) certificate entry
    gets past the directory bound and is rejected as unsigned (-ENODATA).

verify_pefile_signature() is not exported, so the test is built-in only
(bool, not tristate).

Signed-off-by: Fabrice Derepas <fabrice.derepas@canonical.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/asymmetric_keys/Kconfig

@@ -114,4 +114,16 @@ config FIPS_SIGNATURE_SELFTEST_ECDSA
 	depends on CRYPTO_SHA256=y || CRYPTO_SHA256=FIPS_SIGNATURE_SELFTEST
 	depends on CRYPTO_ECDSA=y || CRYPTO_ECDSA=FIPS_SIGNATURE_SELFTEST
 
+config VERIFY_PEFILE_KUNIT_TEST
+	bool "KUnit tests for signed PE file parsing" if !KUNIT_ALL_TESTS
+	depends on KUNIT=y && SIGNED_PE_FILE_VERIFICATION
+	default KUNIT_ALL_TESTS
+	help
+	  Enable KUnit tests for the PE binary parser used by signed PE file
+	  signature verification.  The tests build small malformed PE images in
+	  memory and check that pefile_parse_binary() rejects them instead of
+	  reading out of bounds.
+
+	  If unsure, say N.
+
 endif # ASYMMETRIC_KEY_TYPE

crypto/asymmetric_keys/Makefile

@@ -79,3 +79,5 @@ verify_signed_pefile-y := \
 
 $(obj)/mscode_parser.o: $(obj)/mscode.asn1.h $(obj)/mscode.asn1.h
 $(obj)/mscode.asn1.o: $(obj)/mscode.asn1.c $(obj)/mscode.asn1.h
+
+obj-$(CONFIG_VERIFY_PEFILE_KUNIT_TEST) += verify_pefile_test.o

crypto/asymmetric_keys/verify_pefile_test.c

@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit tests for the signed PE binary parser in verify_pefile.c.
+ *
+ * The cases build small malformed PE images in memory and call
+ * verify_pefile_signature(), which parses the image before any signature
+ * check, so the parser is exercised without a keyring or a real signature.
+ */
+#include <kunit/test.h>
+#include <linux/slab.h>
+#include <linux/pe.h>
+#include <linux/verification.h>
+
+/*
+ * Build a minimal PE32 image whose optional header declares @data_dirs data
+ * directory entries.  header_size is sized to hold them and the image is a few
+ * bytes larger.  With @data_dirs < 5 the certificate table entry (fixed index
+ * 4) lies outside the declared directory.
+ */
+static void *build_pe32(u16 data_dirs, unsigned int *out_len)
+{
+	size_t cursor = sizeof(struct mz_hdr) + sizeof(struct pe_hdr) +
+			sizeof(struct pe32_opt_hdr);
+	size_t header_size = cursor + ((size_t)data_dirs + 1) *
+				      sizeof(struct data_dirent);
+	size_t pelen = header_size + 8;
+	struct mz_hdr *mz;
+	struct pe_hdr *pe;
+	struct pe32_opt_hdr *opt;
+	void *buf = kzalloc(pelen, GFP_KERNEL);
+
+	if (!buf)
+		return NULL;
+
+	mz = buf;
+	mz->magic = IMAGE_DOS_SIGNATURE;
+	mz->peaddr = sizeof(struct mz_hdr);
+
+	pe = buf + sizeof(struct mz_hdr);
+	pe->magic = IMAGE_NT_SIGNATURE;
+
+	opt = buf + sizeof(struct mz_hdr) + sizeof(struct pe_hdr);
+	opt->magic = IMAGE_NT_OPTIONAL_HDR32_MAGIC;
+	opt->header_size = header_size;
+	opt->data_dirs = data_dirs;
+
+	*out_len = pelen;
+	return buf;
+}
+
+/*
+ * data_dirs = 0: the certificate table entry (index 4) is absent, so the
+ * parser must reject the image instead of reading ddir->certs past the end.
+ */
+static void pefile_missing_certs_dirent(struct kunit *test)
+{
+	unsigned int len;
+	void *buf = build_pe32(0, &len);
+	int ret;
+
+	KUNIT_ASSERT_NOT_NULL(test, buf);
+	ret = verify_pefile_signature(buf, len, NULL,
+				      VERIFYING_KEXEC_PE_SIGNATURE);
+	KUNIT_EXPECT_EQ(test, ret, -ELIBBAD);
+	kfree(buf);
+}
+
+/*
+ * data_dirs = 5: the certificate table entry is present (and zero, i.e.
+ * unsigned), so the parser gets past the directory bound and rejects the image
+ * as unsigned (-ENODATA) rather than -ELIBBAD.
+ */
+static void pefile_present_certs_dirent(struct kunit *test)
+{
+	unsigned int len;
+	void *buf = build_pe32(5, &len);
+	int ret;
+
+	KUNIT_ASSERT_NOT_NULL(test, buf);
+	ret = verify_pefile_signature(buf, len, NULL,
+				      VERIFYING_KEXEC_PE_SIGNATURE);
+	KUNIT_EXPECT_EQ(test, ret, -ENODATA);
+	kfree(buf);
+}
+
+static struct kunit_case verify_pefile_cases[] = {
+	KUNIT_CASE(pefile_missing_certs_dirent),
+	KUNIT_CASE(pefile_present_certs_dirent),
+	{}
+};
+
+static struct kunit_suite verify_pefile_suite = {
+	.name = "verify_pefile",
+	.test_cases = verify_pefile_cases,
+};
+
+kunit_test_suite(verify_pefile_suite);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("KUnit tests for the signed PE binary parser");