linux-kernel - [PATCH 2/2 v2] Add self-test for verifying load alignment.

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Date:   Fri, 31 Jul 2020 14:37:44 -0400
From:   Chris Kennelly <ckennelly@...gle.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Song Liu <songliubraving@...com>
Cc:     David Rientjes <rientjes@...gle.com>,
        Ian Rogers <irogers@...gle.com>,
        Hugh Dickens <hughd@...gle.com>,
        Andrew Morton <akpm@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Fangrui Song <maskray@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, Chris Kennelly <ckennelly@...gle.com>
Subject: [PATCH 2/2 v2] Add self-test for verifying load alignment.

This produces a PIE binary with a variety of p_align requirements,
suitable for verifying that the load address meets that alignment
requirement.

Signed-off-by: Chris Kennelly <ckennelly@...gle.com>
---
 tools/testing/selftests/exec/.gitignore     |  1 +
 tools/testing/selftests/exec/Makefile       |  9 ++-
 tools/testing/selftests/exec/load_address.c | 68 +++++++++++++++++++++
 3 files changed, 76 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/exec/load_address.c

diff --git a/tools/testing/selftests/exec/.gitignore b/tools/testing/selftests/exec/.gitignore
index 94b02a18f230b..80f57881e9146 100644
--- a/tools/testing/selftests/exec/.gitignore
+++ b/tools/testing/selftests/exec/.gitignore
@@ -7,6 +7,7 @@ execveat.moved
 execveat.path.ephemeral
 execveat.ephemeral
 execveat.denatured
+/load_address_*
 /recursion-depth
 xxxxxxxx*
 pipe
diff --git a/tools/testing/selftests/exec/Makefile b/tools/testing/selftests/exec/Makefile
index 4453b8f8def37..81cd5d9860629 100644
--- a/tools/testing/selftests/exec/Makefile
+++ b/tools/testing/selftests/exec/Makefile
@@ -4,7 +4,7 @@ CFLAGS += -Wno-nonnull
 CFLAGS += -D_GNU_SOURCE
 
 TEST_PROGS := binfmt_script
-TEST_GEN_PROGS := execveat
+TEST_GEN_PROGS := execveat load_address_4096 load_address_2097152 load_address_16777216
 TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir pipe
 # Makefile is a run-time dependency, since it's accessed by the execveat test
 TEST_FILES := Makefile
@@ -26,4 +26,9 @@ $(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 $< -o $@
+$(OUTPUT)/load_address_2097152: load_address.c
+	$(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=0x200000 -pie $< -o $@
+$(OUTPUT)/load_address_16777216: load_address.c
+	$(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=0x1000000 -pie $< -o $@
diff --git a/tools/testing/selftests/exec/load_address.c b/tools/testing/selftests/exec/load_address.c
new file mode 100644
index 0000000000000..d487c2f6a6150
--- /dev/null
+++ b/tools/testing/selftests/exec/load_address.c
@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+#include <link.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+struct Statistics {
+	unsigned long long load_address;
+	unsigned long long alignment;
+};
+
+int ExtractStatistics(struct dl_phdr_info *info, size_t size, void *data)
+{
+	struct Statistics *stats = (struct Statistics *) data;
+	int i;
+
+	if (info->dlpi_name != NULL && info->dlpi_name[0] != '\0') {
+		// Ignore headers from other than the executable.
+		return 2;
+	}
+
+	stats->load_address = (unsigned long long) info->dlpi_addr;
+	stats->alignment = 0;
+
+	for (i = 0; i < info->dlpi_phnum; i++) {
+		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;
+	}
+
+	return 1;  // Terminate dl_iterate_phdr.
+}
+
+int main(int argc, char **argv)
+{
+	struct Statistics extracted;
+	unsigned long long misalign;
+	int ret;
+
+	ret = dl_iterate_phdr(ExtractStatistics, &extracted);
+	if (ret != 1) {
+		fprintf(stderr, "FAILED\n");
+		return 1;
+	}
+
+	if (extracted.alignment == 0) {
+		fprintf(stderr, "No alignment found\n");
+		return 1;
+	} else if (extracted.alignment & (extracted.alignment - 1)) {
+		fprintf(stderr, "Alignment is not a power of 2\n");
+		return 1;
+	}
+
+	misalign = extracted.load_address & (extracted.alignment - 1);
+	if (misalign) {
+		printf("alignment = %llu, load_address = %llu\n",
+			extracted.alignment, extracted.load_address);
+		fprintf(stderr, "FAILED\n");
+		return 1;
+	}
+
+	fprintf(stderr, "PASS\n");
+	return 0;
+}
-- 
2.28.0.163.g6104cc2f0b6-goog