selftests/exec: Build both static and non-static load_address tests

After commit 4d1cd3b ("tools/testing/selftests/exec: fix link
error"), the load address alignment tests tried to build statically.
This was silently ignored in some cases. However, after attempting to
further fix the build by switching to "-static-pie", the test started
failing. This appears to be due to non-PT_INTERP ET_DYN execs ("static
PIE") not doing alignment correctly, which remains unfixed[1]. See commit
aeb7923 ("revert "fs/binfmt_elf: use PT_LOAD p_align values for
static PIE"") for more details.

Provide rules to build both static and non-static PIE binaries, improve
debug reporting, and perform several test steps instead of a single
all-or-nothing test. However, do not actually enable static-pie tests;
alignment specification is only supported for ET_DYN with PT_INTERP
("regular PIE").

Link: https://bugzilla.kernel.org/show_bug.cgi?id=215275 [1]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Kees Cook <[email protected]>

tools/testing/selftests/exec/Makefile

@@ -3,8 +3,13 @@ CFLAGS = -Wall
 CFLAGS += -Wno-nonnull
 CFLAGS += -D_GNU_SOURCE
 
+ALIGNS := 0x1000 0x200000 0x1000000
+ALIGN_PIES        := $(patsubst %,load_address.%,$(ALIGNS))
+ALIGN_STATIC_PIES := $(patsubst %,load_address.static.%,$(ALIGNS))
+ALIGNMENT_TESTS   := $(ALIGN_PIES)
+
 TEST_PROGS := binfmt_script.py
-TEST_GEN_PROGS := execveat load_address_4096 load_address_2097152 load_address_16777216 non-regular
+TEST_GEN_PROGS := execveat non-regular $(ALIGNMENT_TESTS)
 TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir
 # Makefile is a run-time dependency, since it's accessed by the execveat test
 TEST_FILES := Makefile
@@ -28,9 +33,9 @@ $(OUTPUT)/execveat.symlink: $(OUTPUT)/execveat
 $(OUTPUT)/execveat.denatured: $(OUTPUT)/execveat
 	cp $< $@
 	chmod -x $@
-$(OUTPUT)/load_address_4096: load_address.c
-	$(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=0x1000 -pie -static $< -o $@
-$(OUTPUT)/load_address_2097152: load_address.c
-	$(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=0x200000 -pie -static $< -o $@
-$(OUTPUT)/load_address_16777216: load_address.c
-	$(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=0x1000000 -pie -static $< -o $@
+$(OUTPUT)/load_address.0x%: load_address.c
+	$(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=$(lastword $(subst ., ,$@)) \
+		-fPIE -pie $< -o $@
+$(OUTPUT)/load_address.static.0x%: load_address.c
+	$(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=$(lastword $(subst ., ,$@)) \
+		-fPIE -static-pie $< -o $@

tools/testing/selftests/exec/load_address.c

@@ -5,11 +5,13 @@
 #include <link.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdbool.h>
 #include "../kselftest.h"
 
 struct Statistics {
 	unsigned long long load_address;
 	unsigned long long alignment;
+	bool interp;
 };
 
 int ExtractStatistics(struct dl_phdr_info *info, size_t size, void *data)
@@ -26,39 +28,78 @@ int ExtractStatistics(struct dl_phdr_info *info, size_t size, void *data)
 	stats->alignment = 0;
 
 	for (i = 0; i < info->dlpi_phnum; i++) {
+		unsigned long long align;
+
+		if (info->dlpi_phdr[i].p_type == PT_INTERP) {
+			stats->interp = true;
+			continue;
+		}
+
 		if (info->dlpi_phdr[i].p_type != PT_LOAD)
 			continue;
 
-		if (info->dlpi_phdr[i].p_align > stats->alignment)
-			stats->alignment = info->dlpi_phdr[i].p_align;
+		align = info->dlpi_phdr[i].p_align;
+
+		if (align > stats->alignment)
+			stats->alignment = align;
 	}
 
 	return 1;  // Terminate dl_iterate_phdr.
 }
 
 int main(int argc, char **argv)
 {
-	struct Statistics extracted;
-	unsigned long long misalign;
+	struct Statistics extracted = { };
+	unsigned long long misalign, pow2;
+	bool interp_needed;
+	char buf[1024];
+	FILE *maps;
 	int ret;
 
 	ksft_print_header();
-	ksft_set_plan(1);
+	ksft_set_plan(4);
+
+	/* Dump maps file for debugging reference. */
+	maps = fopen("/proc/self/maps", "r");
+	if (!maps)
+		ksft_exit_fail_msg("FAILED: /proc/self/maps: %s\n", strerror(errno));
+	while (fgets(buf, sizeof(buf), maps)) {
+		ksft_print_msg("%s", buf);
+	}
+	fclose(maps);
 
+	/* Walk the program headers. */
 	ret = dl_iterate_phdr(ExtractStatistics, &extracted);
 	if (ret != 1)
 		ksft_exit_fail_msg("FAILED: dl_iterate_phdr\n");
 
-	if (extracted.alignment == 0)
-		ksft_exit_fail_msg("FAILED: No alignment found\n");
-	else if (extracted.alignment & (extracted.alignment - 1))
-		ksft_exit_fail_msg("FAILED: Alignment is not a power of 2\n");
+	/* Report our findings. */
+	ksft_print_msg("load_address=%#llx alignment=%#llx\n",
+		       extracted.load_address, extracted.alignment);
+
+	/* If we're named with ".static." we expect no INTERP. */
+	interp_needed = strstr(argv[0], ".static.") == NULL;
+
+	/* Were we built as expected? */
+	ksft_test_result(interp_needed == extracted.interp,
+			 "%s INTERP program header %s\n",
+			 interp_needed ? "Wanted" : "Unwanted",
+			 extracted.interp ? "seen" : "missing");
+
+	/* Did we find an alignment? */
+	ksft_test_result(extracted.alignment != 0,
+			 "Alignment%s found\n", extracted.alignment ? "" : " NOT");
+
+	/* Is the alignment sane? */
+	pow2 = extracted.alignment & (extracted.alignment - 1);
+	ksft_test_result(pow2 == 0,
+			 "Alignment is%s a power of 2: %#llx\n",
+			 pow2 == 0 ? "" : " NOT", extracted.alignment);
 
+	/* Is the load address aligned? */
 	misalign = extracted.load_address & (extracted.alignment - 1);
-	if (misalign)
-		ksft_exit_fail_msg("FAILED: alignment = %llu, load_address = %llu\n",
-				   extracted.alignment, extracted.load_address);
+	ksft_test_result(misalign == 0, "Load Address is %saligned (%#llx)\n",
+			 misalign ? "MIS" : "", misalign);
 
-	ksft_test_result_pass("Completed\n");
 	ksft_finished();
 }