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From:   Sidhartha Kumar <sidhartha.kumar@oracle.com>
To:     shuah@kernel.org, akpm@linux-foundation.org
Cc:     Sidhartha Kumar <sidhartha.kumar@oracle.com>, linux-mm@kvack.org,
        linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 1/4] selftest/vm: verify mmap addr in mremap_test
Date:   Thu, 14 Apr 2022 17:15:26 +0000
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Avoid calling mmap with requested addresses that
are less than the system's mmap_min_addr. Running
the test as root returns EACCES when trying to map
addresses < mmap_min_addr which is not one of the
error codes for the retry condition. Add a munmap
call after an alignment check as the mappings are
retained after the retry and can reach vm.max_map_count.

Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
---
 tools/testing/selftests/vm/mremap_test.c | 41 +++++++++++++++++++++++-
 1 file changed, 40 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/vm/mremap_test.c b/tools/testing/selftests/vm/mremap_test.c
index 0624d1bd71b5..58600fee4b81 100644
--- a/tools/testing/selftests/vm/mremap_test.c
+++ b/tools/testing/selftests/vm/mremap_test.c
@@ -6,6 +6,7 @@
 
 #include <errno.h>
 #include <stdlib.h>
+#include <stdio.h>
 #include <string.h>
 #include <sys/mman.h>
 #include <time.h>
@@ -64,6 +65,35 @@ enum {
 	.expect_failure = should_fail				\
 }
 
+/* Returns mmap_min_addr sysctl */
+static unsigned long long get_mmap_min_addr(void)
+{
+	FILE *fp;
+	int n_matched;
+	static unsigned long long addr;
+
+	if (addr)
+		return addr;
+
+	fp = fopen("/proc/sys/vm/mmap_min_addr", "r");
+	if (fp == NULL) {
+		ksft_print_msg("Failed to open /proc/sys/vm/mmap_min_addr: %s\n",
+			strerror(errno));
+		exit(KSFT_SKIP);
+	}
+
+	n_matched = fscanf(fp, "%llu", &addr);
+	if (n_matched != 1) {
+		ksft_print_msg("Failed to read /proc/sys/vm/mmap_min_addr: %s\n",
+			strerror(errno));
+		fclose(fp);
+		exit(KSFT_SKIP);
+	}
+
+	fclose(fp);
+	return addr;
+}
+
 /*
  * Returns the start address of the mapping on success, else returns
  * NULL on failure.
@@ -72,8 +102,15 @@ static void *get_source_mapping(struct config c)
 {
 	unsigned long long addr = 0ULL;
 	void *src_addr = NULL;
+	unsigned long long mmap_min_addr;
+
+	mmap_min_addr = get_mmap_min_addr();
+
 retry:
 	addr += c.src_alignment;
+	if (addr < mmap_min_addr)
+		goto retry;
+
 	src_addr = mmap((void *) addr, c.region_size, PROT_READ | PROT_WRITE,
 			MAP_FIXED_NOREPLACE | MAP_ANONYMOUS | MAP_SHARED,
 			-1, 0);
@@ -91,8 +128,10 @@ static void *get_source_mapping(struct config c)
 	 * alignment in the tests.
 	 */
 	if (((unsigned long long) src_addr & (c.src_alignment - 1)) ||
-			!((unsigned long long) src_addr & c.src_alignment))
+			!((unsigned long long) src_addr & c.src_alignment)) {
+		munmap(src_addr, c.region_size);
 		goto retry;
+	}
 
 	if (!src_addr)
 		goto error;
-- 
2.27.0