[PATCH v3 1/9] 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>
---
v2->v3:
 - Split into multiple testcases

 tools/testing/selftests/arm/mm/compat_va.c | 89 ++++++++++++++++++++++
 1 file changed, 89 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..20aa419eff29
--- /dev/null
+++ b/tools/testing/selftests/arm/mm/compat_va.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * 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 ret;
+	int i;
+
+	ksft_print_header();
+	ksft_set_plan(2);
+
+	/* 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;
+
+	ret = (chunks < NR_CHUNKS_4G);
+	ksft_test_result(ret, "mmapped chunks under 4GB\n");
+
+	/* parse /proc/self/maps, confirm 32 bit VA mappings */
+	file = fopen("/proc/self/maps", "r");
+	if (!file)
+		ksft_exit_fail_perror("/proc/self/maps");
+
+	ret = 0;
+	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_exit_fail_msg("Unexpected format\n");
+
+		ret |= ((hyphen_loc - line > 8) ||
+			(whitespace_loc - hyphen_loc > 9));
+	}
+
+	ksft_test_result(!ret, "Memory map within 32 bits\n");
+
+	for (i = 0; i < chunks; ++i)
+		munmap(ptr[i], MAP_CHUNK_SIZE);
+
+	ksft_finished();
+}
-- 
2.39.2