lib/842: add KUnit tests for the decompressor

Add table-driven tests for the 842 decompressor's output and history
validation.

Three malformed streams cover an indexed copy larger than the remaining
output, short data larger than the remaining output, and a repeat after
fewer than eight output bytes. Every case checks the return value, output
length and fixed guard bands on both sides of the output. Successful cases
also check complete contents from a poison-filled destination. The repeat
vector's CRC includes the leading guard byte, so the unfixed decoder
successfully validates the CRC after reading before the buffer.

Three valid streams cover the same boundaries at equality: an I8 index
consuming the final eight bytes, five short-data bytes consuming the final
five, and a repeat with exactly one block of history.

On an unmodified baseline the malformed cases fail and the boundary cases
pass; with the preceding fixes all six pass.

Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

MAINTAINERS

@@ -12459,6 +12459,7 @@ F:	drivers/crypto/nx/Makefile
 F:	drivers/crypto/nx/nx-842*
 F:	include/linux/sw842.h
 F:	lib/842/
+F:	lib/tests/842_decompress_kunit.c
 
 IBM Power in-Nest Crypto Acceleration
 M:	Breno Leitão <leitao@debian.org>

lib/Kconfig.debug

@@ -2225,6 +2225,21 @@ menuconfig RUNTIME_TESTING_MENU
 
 if RUNTIME_TESTING_MENU
 
+config 842_DECOMPRESS_KUNIT_TEST
+	tristate "KUnit tests for the 842 decompressor" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	select 842_DECOMPRESS
+	default KUNIT_ALL_TESTS
+	help
+	  Enable stream-validation and boundary tests for the software 842
+	  decompressor. The tests exercise indexed copies, short data and
+	  repeat operations at valid and invalid output or history boundaries.
+
+	  For more information on KUnit and unit tests in general, refer to
+	  Documentation/dev-tools/kunit/.
+
+	  If unsure, say N.
+
 config TEST_DHRY
 	tristate "Dhrystone benchmark test"
 	help

lib/tests/842_decompress_kunit.c

@@ -0,0 +1,144 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <kunit/test.h>
+#include <linux/sw842.h>
+
+#define SW842_GUARD_SIZE	8
+#define SW842_MAX_OUTPUT	16
+#define SW842_GUARD_BYTE	0x42
+#define SW842_OUTPUT_POISON	0x5a
+
+/* ZEROS, I8(0), END, CRC32. */
+static const u8 sw842_index_exact_fit[] = {
+	0xe6, 0x40, 0x3c, 0x00, 0x00, 0x00, 0x00,
+};
+
+/* D8(eight zero bytes), I8(0), END, CRC32. */
+static const u8 sw842_index_output_overflow[] = {
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x06, 0x40, 0x3c, 0x00, 0x00, 0x00, 0x00,
+};
+
+/* ZEROS, SHORT_DATA(01 02 03 04 05), END, CRC32. */
+static const u8 sw842_short_data_exact_fit[] = {
+	0xe7, 0x68, 0x08, 0x10, 0x18, 0x20,
+	0x2f, 0xa9, 0x67, 0xfc, 0x07, 0xc0,
+};
+
+/* ZEROS, SHORT_DATA(five zero bytes), END, CRC32. */
+static const u8 sw842_short_data_output_overflow[] = {
+	0xe7, 0x48, 0x07, 0x80, 0x00, 0x00, 0x00, 0x00,
+};
+
+/* ZEROS, REPEAT(one block), END, CRC32. */
+static const u8 sw842_repeat_exact_history[] = {
+	0xe6, 0xc0, 0xf0, 0x00, 0x00, 0x00, 0x00,
+};
+
+/*
+ * SHORT_DATA(seven zero bytes), REPEAT(one block), END, CRC32.
+ * CRC32 includes SW842_GUARD_BYTE copied from before output into byte 7.
+ */
+static const u8 sw842_repeat_without_full_history[] = {
+	0xef, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0xd8, 0x1e, 0x09, 0xa3, 0x1d, 0xd6,
+};
+
+static const u8 sw842_zero_output[SW842_MAX_OUTPUT];
+static const u8 sw842_short_data_output[] = {
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x01, 0x02, 0x03, 0x04, 0x05,
+};
+
+struct sw842_decompress_test_case {
+	const char *name;
+	const u8 *compressed;
+	unsigned int compressed_len;
+	const u8 *expected_output;
+	unsigned int output_capacity;
+	int expected_ret;
+};
+
+#define SW842_DECOMPRESS_CASE(_name, _compressed, _compressed_len, _expected, \
+			      _capacity, _ret) \
+	{ \
+		.name = _name, \
+		.compressed = _compressed, \
+		.compressed_len = _compressed_len, \
+		.expected_output = _expected, \
+		.output_capacity = _capacity, \
+		.expected_ret = _ret, \
+	}
+
+static const struct sw842_decompress_test_case sw842_decompress_cases[] = {
+	SW842_DECOMPRESS_CASE("index_exact_fit", sw842_index_exact_fit,
+			      ARRAY_SIZE(sw842_index_exact_fit),
+			      sw842_zero_output, 16, 0),
+	SW842_DECOMPRESS_CASE("index_output_overflow",
+			      sw842_index_output_overflow,
+			      ARRAY_SIZE(sw842_index_output_overflow),
+			      sw842_zero_output, 8, -ENOSPC),
+	SW842_DECOMPRESS_CASE("short_data_exact_fit",
+			      sw842_short_data_exact_fit,
+			      ARRAY_SIZE(sw842_short_data_exact_fit),
+			      sw842_short_data_output,
+			      sizeof(sw842_short_data_output), 0),
+	SW842_DECOMPRESS_CASE("short_data_output_overflow",
+			      sw842_short_data_output_overflow,
+			      ARRAY_SIZE(sw842_short_data_output_overflow),
+			      sw842_zero_output, 8, -ENOSPC),
+	SW842_DECOMPRESS_CASE("repeat_exact_history",
+			      sw842_repeat_exact_history,
+			      ARRAY_SIZE(sw842_repeat_exact_history),
+			      sw842_zero_output, 16, 0),
+	SW842_DECOMPRESS_CASE("repeat_without_full_history",
+			      sw842_repeat_without_full_history,
+			      ARRAY_SIZE(sw842_repeat_without_full_history),
+			      sw842_zero_output, 15, -EINVAL),
+};
+
+KUNIT_ARRAY_PARAM_DESC(sw842_decompress, sw842_decompress_cases, name);
+
+static void sw842_decompress_test(struct kunit *test)
+{
+	const struct sw842_decompress_test_case *test_case = test->param_value;
+	u8 storage[SW842_GUARD_SIZE + SW842_MAX_OUTPUT + SW842_GUARD_SIZE];
+	u8 expected_guard[SW842_GUARD_SIZE];
+	u8 *output = storage + SW842_GUARD_SIZE;
+	unsigned int output_len = test_case->output_capacity;
+	int ret;
+
+	KUNIT_ASSERT_LE(test, test_case->output_capacity, SW842_MAX_OUTPUT);
+	memset(storage, SW842_GUARD_BYTE, sizeof(storage));
+	memset(expected_guard, SW842_GUARD_BYTE, sizeof(expected_guard));
+	memset(output, SW842_OUTPUT_POISON, test_case->output_capacity);
+
+	ret = sw842_decompress(test_case->compressed,
+			       test_case->compressed_len, output, &output_len);
+
+	KUNIT_EXPECT_EQ(test, ret, test_case->expected_ret);
+	/* Every successful case is an exact-fit boundary test. */
+	KUNIT_EXPECT_EQ(test, output_len,
+			test_case->expected_ret ? 0U : test_case->output_capacity);
+	if (!test_case->expected_ret)
+		KUNIT_EXPECT_MEMEQ(test, output, test_case->expected_output,
+				   test_case->output_capacity);
+	KUNIT_EXPECT_MEMEQ(test, storage, expected_guard, SW842_GUARD_SIZE);
+	KUNIT_EXPECT_MEMEQ(test, output + test_case->output_capacity,
+			   expected_guard, SW842_GUARD_SIZE);
+}
+
+static struct kunit_case sw842_decompress_test_cases[] = {
+	KUNIT_CASE_PARAM(sw842_decompress_test, sw842_decompress_gen_params),
+	{}
+};
+
+static struct kunit_suite sw842_decompress_test_suite = {
+	.name = "842-decompress",
+	.test_cases = sw842_decompress_test_cases,
+};
+
+kunit_test_suite(sw842_decompress_test_suite);
+
+MODULE_DESCRIPTION("Software 842 decompressor KUnit tests");
+MODULE_LICENSE("GPL");

lib/tests/Makefile

@@ -4,6 +4,7 @@
 
 # KUnit tests
 CFLAGS_bitfield_kunit.o := $(DISABLE_STRUCTLEAK_PLUGIN)
+obj-$(CONFIG_842_DECOMPRESS_KUNIT_TEST) += 842_decompress_kunit.o
 obj-$(CONFIG_BASE64_KUNIT) += base64_kunit.o
 obj-$(CONFIG_BITOPS_KUNIT) += bitops_kunit.o
 obj-$(CONFIG_BITFIELD_KUNIT) += bitfield_kunit.o