fortify: Add compile-time FORTIFY_SOURCE tests

While the run-time testing of FORTIFY_SOURCE is already present in
LKDTM, there is no testing of the expected compile-time detections. In
preparation for correctly supporting FORTIFY_SOURCE under Clang, adding
additional FORTIFY_SOURCE defenses, and making sure FORTIFY_SOURCE
doesn't silently regress with GCC, introduce a build-time test suite that
checks each expected compile-time failure condition.

As this is relatively backwards from standard build rules in the
sense that a successful test is actually a compile _failure_, create
a wrapper script to check for the correct errors, and wire it up as
a dummy dependency to lib/string.o, collecting the results into a log
file artifact.

Signed-off-by: Kees Cook <[e-mail]>

MAINTAINERS

···
 S:	Maintained
 F:	drivers/net/ethernet/nvidia/*
 
+FORTIFY_SOURCE
+M:	Kees Cook <[e-mail]>
+L:	[e-mail]
+S:	Supported
+F:	include/linux/fortify-string.h
+F:	lib/test_fortify/*
+F:	scripts/test_fortify.sh
+K:	\b__NO_FORTIFY\b
+
 FPGA DFL DRIVERS
 M:	Wu Hao <[e-mail]>
 R:	Tom Rix <[e-mail]>

lib/.gitignore

···
 /gen_crc32table
 /gen_crc64table
 /oid_registry_data.c
+/test_fortify.log
+/test_fortify/*.log

lib/Makefile

···
 obj-$(CONFIG_SLUB_KUNIT_TEST) += slub_kunit.o
 
 obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
+
+# FORTIFY_SOURCE compile-time behavior tests
+TEST_FORTIFY_SRCS = $(wildcard $(srctree)/$(src)/test_fortify/*-*.c)
+TEST_FORTIFY_LOGS = $(patsubst $(srctree)/$(src)/%.c, %.log, $(TEST_FORTIFY_SRCS))
+TEST_FORTIFY_LOG = test_fortify.log
+
+quiet_cmd_test_fortify = TEST    $@
+      cmd_test_fortify = $(CONFIG_SHELL) $(srctree)/scripts/test_fortify.sh \
+			$< $@ "$(NM)" $(CC) $(c_flags) \
+			$(call cc-disable-warning,fortify-source)
+
+targets += $(TEST_FORTIFY_LOGS)
+clean-files += $(TEST_FORTIFY_LOGS)
+clean-files += $(addsuffix .o, $(TEST_FORTIFY_LOGS))
+$(obj)/test_fortify/%.log: $(src)/test_fortify/%.c \
+			   $(src)/test_fortify/test_fortify.h \
+			   $(srctree)/include/linux/fortify-string.h \
+			   $(srctree)/scripts/test_fortify.sh \
+			   FORCE
+	$(call if_changed,test_fortify)
+
+quiet_cmd_gen_fortify_log = GEN     $@
+      cmd_gen_fortify_log = cat </dev/null $(filter-out FORCE,$^) 2>/dev/null > $@ || true
+
+targets += $(TEST_FORTIFY_LOG)
+clean-files += $(TEST_FORTIFY_LOG)
+$(obj)/$(TEST_FORTIFY_LOG): $(addprefix $(obj)/, $(TEST_FORTIFY_LOGS)) FORCE
+	$(call if_changed,gen_fortify_log)
+
+# Fake dependency to trigger the fortify tests.
+ifeq ($(CONFIG_FORTIFY_SOURCE),y)
+$(obj)/string.o: $(obj)/$(TEST_FORTIFY_LOG)
+endif

lib/test_fortify/read_overflow-memchr.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memchr(small, 0x7A, sizeof(small) + 1)
+
+#include "test_fortify.h"

lib/test_fortify/read_overflow-memchr_inv.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memchr_inv(small, 0x7A, sizeof(small) + 1)
+
+#include "test_fortify.h"

lib/test_fortify/read_overflow-memcmp.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memcmp(small, large, sizeof(small) + 1)
+
+#include "test_fortify.h"

lib/test_fortify/read_overflow-memscan.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memscan(small, 0x7A, sizeof(small) + 1)
+
+#include "test_fortify.h"

lib/test_fortify/read_overflow2-memcmp.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memcmp(large, small, sizeof(small) + 1)
+
+#include "test_fortify.h"

lib/test_fortify/read_overflow2-memcpy.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memcpy(large, instance.buf, sizeof(large))
+
+#include "test_fortify.h"

lib/test_fortify/read_overflow2-memmove.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memmove(large, instance.buf, sizeof(large))
+
+#include "test_fortify.h"

lib/test_fortify/test_fortify.h

···
+/* SPDX-License-Identifier: GPL-2.0-only */
+#include <linux/kernel.h>
+#include <linux/printk.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+void do_fortify_tests(void);
+
+#define __BUF_SMALL	16
+#define __BUF_LARGE	32
+struct fortify_object {
+	int a;
+	char buf[__BUF_SMALL];
+	int c;
+};
+
+#define LITERAL_SMALL "AAAAAAAAAAAAAAA"
+#define LITERAL_LARGE "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
+const char small_src[__BUF_SMALL] = LITERAL_SMALL;
+const char large_src[__BUF_LARGE] = LITERAL_LARGE;
+
+char small[__BUF_SMALL];
+char large[__BUF_LARGE];
+struct fortify_object instance;
+size_t size;
+
+void do_fortify_tests(void)
+{
+	/* Normal initializations. */
+	memset(&instance, 0x32, sizeof(instance));
+	memset(small, 0xA5, sizeof(small));
+	memset(large, 0x5A, sizeof(large));
+
+	TEST;
+}

lib/test_fortify/write_overflow-memcpy.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memcpy(instance.buf, large_src, sizeof(large_src))
+
+#include "test_fortify.h"

lib/test_fortify/write_overflow-memmove.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memmove(instance.buf, large_src, sizeof(large_src))
+
+#include "test_fortify.h"

lib/test_fortify/write_overflow-memset.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memset(instance.buf, 0x5A, sizeof(large_src))
+
+#include "test_fortify.h"

lib/test_fortify/write_overflow-strcpy-lit.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	strcpy(small, LITERAL_LARGE)
+
+#include "test_fortify.h"

lib/test_fortify/write_overflow-strcpy.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	strcpy(small, large_src)
+
+#include "test_fortify.h"

lib/test_fortify/write_overflow-strlcpy-src.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	strlcpy(small, large_src, sizeof(small) + 1)
+
+#include "test_fortify.h"

lib/test_fortify/write_overflow-strlcpy.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	strlcpy(instance.buf, large_src, sizeof(instance.buf) + 1)
+
+#include "test_fortify.h"

lib/test_fortify/write_overflow-strncpy-src.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	strncpy(small, large_src, sizeof(small) + 1)
+
+#include "test_fortify.h"

lib/test_fortify/write_overflow-strncpy.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	strncpy(instance.buf, large_src, sizeof(instance.buf) + 1)
+
+#include "test_fortify.h"

lib/test_fortify/write_overflow-strscpy.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	strscpy(instance.buf, large_src, sizeof(instance.buf) + 1)
+
+#include "test_fortify.h"

scripts/test_fortify.sh

···
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+set -e
+
+# Argument 1: Source file to build.
+IN="$1"
+shift
+# Extract just the filename for error messages below.
+FILE="${IN##*/}"
+# Extract the function name for error messages below.
+FUNC="${FILE#*-}"
+FUNC="${FUNC%%-*}"
+FUNC="${FUNC%%.*}"
+# Extract the symbol to test for in build/symbol test below.
+WANT="__${FILE%%-*}"
+
+# Argument 2: Where to write the build log.
+OUT="$1"
+shift
+TMP="${OUT}.tmp"
+
+# Argument 3: Path to "nm" tool.
+NM="$1"
+shift
+
+# Remaining arguments are: $(CC) $(c_flags)
+
+# Clean up temporary file at exit.
+__cleanup() {
+	rm -f "$TMP"
+}
+trap __cleanup EXIT
+
+# Function names in warnings are wrapped in backticks under UTF-8 locales.
+# Run the commands with LANG=C so that grep output will not change.
+export LANG=C
+
+status=
+# Attempt to build a source that is expected to fail with a specific warning.
+if "$@" -Werror -c "$IN" -o "$OUT".o 2> "$TMP" ; then
+	# If the build succeeds, either the test has failed or the
+	# warning may only happen at link time (Clang). In that case,
+	# make sure the expected symbol is unresolved in the symbol list.
+	# If so, FORTIFY is working for this case.
+	if ! $NM -A "$OUT".o | grep -m1 "\bU ${WANT}$" >>"$TMP" ; then
+		status="warning: unsafe ${FUNC}() usage lacked '$WANT' symbol in $IN"
+	fi
+else
+	# If the build failed, check for the warning in the stderr (gcc).
+	if ! grep -q -m1 "error: call to .\b${WANT}\b." "$TMP" ; then
+		status="warning: unsafe ${FUNC}() usage lacked '$WANT' warning in $IN"
+	fi
+fi
+
+if [ -n "$status" ]; then
+	# Report on failure results, including compilation warnings.
+	echo "$status" | tee "$OUT" >&2
+else
+	# Report on good results, and save any compilation output to log.
+	echo "ok: unsafe ${FUNC}() usage correctly detected with '$WANT' in $IN" >"$OUT"
+fi
+cat "$TMP" >>"$OUT"