[PATCH v2 1/4] selftests/arm: Add mm test

[Dev Jain]

This patch tests the 4GB VA restriction for 32-bit processes; it is required
to test the compat layer, whether the kernel knows that it is running a 32-bit
process or not. Chunks are allocated until the VA gets exhausted; mmap must
fail beyond 4GB. This is asserted against the VA mappings found
in /proc/self/maps.

Signed-off-by: Dev Jain <dev.jain at arm.com>
---
 tools/testing/selftests/arm/mm/compat_va.c | 92 ++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 tools/testing/selftests/arm/mm/compat_va.c

diff --git a/tools/testing/selftests/arm/mm/compat_va.c b/tools/testing/selftests/arm/mm/compat_va.c
new file mode 100644
index 000000000000..03f662fad79f
--- /dev/null
+++ b/tools/testing/selftests/arm/mm/compat_va.c
@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2024 ARM Limited
+ *
+ * Author : Dev Jain <dev.jain at arm.com>
+ *
+ * Tests 4GB VA restriction for 32 bit process
+ */
+
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/mman.h>
+
+#include <linux/sizes.h>
+#include <kselftest.h>
+
+#define MAP_CHUNK_SIZE	SZ_1M
+#define NR_CHUNKS_4G	(SZ_1G / MAP_CHUNK_SIZE) * 4	/* prevent overflow */
+
+static int validate_address_hint(void)
+{
+	char *ptr;
+
+	ptr = mmap((void *) (1UL << 29), MAP_CHUNK_SIZE, PROT_READ |
+		   PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+
+	if (ptr == MAP_FAILED)
+		return 0;
+
+	return -1;
+}
+
+int main(int argc, char *argv[])
+{
+	char *ptr[NR_CHUNKS_4G + 3];
+	char line[1000];
+	int chunks;
+	FILE *file;
+	int i;
+
+	ksft_print_header();
+	ksft_set_plan(1);
+
+	/* try allocation beyond 4 GB */
+	for (i = 0; i < NR_CHUNKS_4G + 3; ++i) {
+		ptr[i] = mmap(NULL, MAP_CHUNK_SIZE, PROT_READ | PROT_WRITE,
+			      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+
+		if (ptr[i] == MAP_FAILED) {
+			if (validate_address_hint())
+				ksft_exit_fail_msg("VA exhaustion failed\n");
+			break;
+		}
+	}
+
+	chunks = i;
+	if (chunks >= NR_CHUNKS_4G) {
+		ksft_test_result_fail("mmapped chunks beyond 4GB\n");
+		ksft_finished();
+	}
+
+	/* parse /proc/self/maps, confirm 32 bit VA mappings */
+	file = fopen("/proc/self/maps", "r");
+	if (file == NULL)
+		ksft_exit_fail_msg("/proc/self/maps cannot be opened\n");
+
+	while (fgets(line, sizeof(line), file)) {
+		const char *whitespace_loc, *hyphen_loc;
+
+		hyphen_loc = strchr(line, '-');
+		whitespace_loc = strchr(line, ' ');
+
+		if (!(hyphen_loc && whitespace_loc)) {
+			ksft_test_result_skip("Unexpected format");
+			ksft_finished();
+		}
+
+		if ((hyphen_loc - line > 8) ||
+		    (whitespace_loc - hyphen_loc) > 9) {
+			ksft_test_result_fail("Memory map more than 32 bits\n");
+			ksft_finished();
+		}
+	}
+
+	for (int i = 0; i < chunks; ++i)
+		munmap(ptr[i], MAP_CHUNK_SIZE);
+
+	ksft_test_result_pass("Test\n");
+	ksft_finished();
+}
-- 
2.39.2