selftest/vm: verify remap destination address in mremap_test

[ Upstream commit 18d609daa546c919fd36b62a7b510c18de4b4af8 ]

Because mremap does not have a MAP_FIXED_NOREPLACE flag, it can destroy
existing mappings.  This causes a segfault when regions such as text are
remapped and the permissions are changed.

Verify the requested mremap destination address does not overlap any
existing mappings by using mmap's MAP_FIXED_NOREPLACE flag.  Keep
incrementing the destination address until a valid mapping is found or
fail the current test once the max address is reached.

Link: https://lkml.kernel.org/r/20220420215721.4868-2-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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/testing/selftests/vm/mremap_test.c b/tools/testing/selftests/vm/mremap_test.c
index efcbf537b3d575ebe496d9d5daa114f5ab45a7f0..8f4dbbd60c09ca9f44173b7669f9948e1fb1b83f 100644 (file)
--- a/tools/testing/selftests/vm/mremap_test.c
+++ b/tools/testing/selftests/vm/mremap_test.c
@@ -66,6 +66,30 @@ enum {
        .expect_failure = should_fail                           \
 }
 
+/*
+ * Returns false if the requested remap region overlaps with an
+ * existing mapping (e.g text, stack) else returns true.
+ */
+static bool is_remap_region_valid(void *addr, unsigned long long size)
+{
+       void *remap_addr = NULL;
+       bool ret = true;
+
+       /* Use MAP_FIXED_NOREPLACE flag to ensure region is not mapped */
+       remap_addr = mmap(addr, size, PROT_READ | PROT_WRITE,
+                                        MAP_FIXED_NOREPLACE | MAP_ANONYMOUS | MAP_SHARED,
+                                        -1, 0);
+
+       if (remap_addr == MAP_FAILED) {
+               if (errno == EEXIST)
+                       ret = false;
+       } else {
+               munmap(remap_addr, size);
+       }
+
+       return ret;
+}
+
 /* Returns mmap_min_addr sysctl tunable from procfs */
 static unsigned long long get_mmap_min_addr(void)
 {