selftest/vm: verify mmap addr in mremap_test

Avoid calling mmap with requested addresses that are less than the
system's mmap_min_addr.  When run as root, mmap returns EACCES when
trying to map addresses < mmap_min_addr.  This is not one of the error
codes for the condition to retry the mmap in the test.

Rather than arbitrarily retrying on EACCES, don't attempt an mmap until
addr > vm.mmap_min_addr.

Add a munmap call after an alignment check as the mappings are retained
after the retry and can reach the vm.max_map_count sysctl.

Link: https://lkml.kernel.org/r/20220420215721.4868-1-sidhartha.kumar@oracle.com
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/tools/testing/selftests/vm/mremap_test.c b/tools/testing/selftests/vm/mremap_test.c
index 7c0b0617b9f85554d6831f15ce5691b9e0082ff7..9a518fee630679981b40424fc8129dd3fe667a21 100644 (file)
--- 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>
@@ -63,6 +64,35 @@ enum {
        .expect_failure = should_fail                           \
 }
 
+/* Returns mmap_min_addr sysctl tunable from procfs */
+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.
@@ -71,8 +101,15 @@ 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);
@@ -90,8 +127,10 @@ retry:
         * 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;