tools/testing/selftests/vm/map_fixed_noreplace.c: add test for MAP_FIXED_NOREPLACE

Add a test for MAP_FIXED_NOREPLACE, based on some code originally by Jann
Horn.  This would have caught the overlap bug reported by Daniel Micay.

I originally suggested to Michal that we create MAP_FIXED_NOREPLACE, but
instead of writing a selftest I spent my time bike-shedding whether it
should be called MAP_FIXED_SAFE/NOCLOBBER/WEAK/NEW ..  mea culpa.

Link: http://lkml.kernel.org/r/20181013133929.28653-1-mpe@ellerman.id.au
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Khalid Aziz <khalid.aziz@oracle.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Jann Horn <jannh@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Abdul Haleem <abdhalee@linux.vnet.ibm.com>
Cc: Joel Stanley <joel@jms.id.au>
Cc: Jason Evans <jasone@google.com>
Cc: David Goldblatt <davidtgoldblatt@gmail.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/.gitignore

@@ -13,3 +13,4 @@ mlock-random-test
 virtual_address_range
 gup_benchmark
 va_128TBswitch
+map_fixed_noreplace

tools/testing/selftests/vm/Makefile

@@ -12,6 +12,7 @@ TEST_GEN_FILES += gup_benchmark
 TEST_GEN_FILES += hugepage-mmap
 TEST_GEN_FILES += hugepage-shm
 TEST_GEN_FILES += map_hugetlb
+TEST_GEN_FILES += map_fixed_noreplace
 TEST_GEN_FILES += map_populate
 TEST_GEN_FILES += mlock-random-test
 TEST_GEN_FILES += mlock2-tests

tools/testing/selftests/vm/map_fixed_noreplace.c

@@ -0,0 +1,206 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Test that MAP_FIXED_NOREPLACE works.
+ *
+ * Copyright 2018, Jann Horn <jannh@google.com>
+ * Copyright 2018, Michael Ellerman, IBM Corporation.
+ */
+
+#include <sys/mman.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#ifndef MAP_FIXED_NOREPLACE
+#define MAP_FIXED_NOREPLACE 0x100000
+#endif
+
+#define BASE_ADDRESS	(256ul * 1024 * 1024)
+
+
+static void dump_maps(void)
+{
+	char cmd[32];
+
+	snprintf(cmd, sizeof(cmd), "cat /proc/%d/maps", getpid());
+	system(cmd);
+}
+
+int main(void)
+{
+	unsigned long flags, addr, size, page_size;
+	char *p;
+
+	page_size = sysconf(_SC_PAGE_SIZE);
+
+	flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED_NOREPLACE;
+
+	// Check we can map all the areas we need below
+	errno = 0;
+	addr = BASE_ADDRESS;
+	size = 5 * page_size;
+	p = mmap((void *)addr, size, PROT_NONE, flags, -1, 0);
+
+	printf("mmap() @ 0x%lx-0x%lx p=%p result=%m\n", addr, addr + size, p);
+
+	if (p == MAP_FAILED) {
+		dump_maps();
+		printf("Error: couldn't map the space we need for the test\n");
+		return 1;
+	}
+
+	errno = 0;
+	if (munmap((void *)addr, 5 * page_size) != 0) {
+		dump_maps();
+		printf("Error: munmap failed!?\n");
+		return 1;
+	}
+	printf("unmap() successful\n");
+
+	errno = 0;
+	addr = BASE_ADDRESS + page_size;
+	size = 3 * page_size;
+	p = mmap((void *)addr, size, PROT_NONE, flags, -1, 0);
+	printf("mmap() @ 0x%lx-0x%lx p=%p result=%m\n", addr, addr + size, p);
+
+	if (p == MAP_FAILED) {
+		dump_maps();
+		printf("Error: first mmap() failed unexpectedly\n");
+		return 1;
+	}
+
+	/*
+	 * Exact same mapping again:
+	 *   base |  free  | new
+	 *     +1 | mapped | new
+	 *     +2 | mapped | new
+	 *     +3 | mapped | new
+	 *     +4 |  free  | new
+	 */
+	errno = 0;
+	addr = BASE_ADDRESS;
+	size = 5 * page_size;
+	p = mmap((void *)addr, size, PROT_NONE, flags, -1, 0);
+	printf("mmap() @ 0x%lx-0x%lx p=%p result=%m\n", addr, addr + size, p);
+
+	if (p != MAP_FAILED) {
+		dump_maps();
+		printf("Error:1: mmap() succeeded when it shouldn't have\n");
+		return 1;
+	}
+
+	/*
+	 * Second mapping contained within first:
+	 *
+	 *   base |  free  |
+	 *     +1 | mapped |
+	 *     +2 | mapped | new
+	 *     +3 | mapped |
+	 *     +4 |  free  |
+	 */
+	errno = 0;
+	addr = BASE_ADDRESS + (2 * page_size);
+	size = page_size;
+	p = mmap((void *)addr, size, PROT_NONE, flags, -1, 0);
+	printf("mmap() @ 0x%lx-0x%lx p=%p result=%m\n", addr, addr + size, p);
+
+	if (p != MAP_FAILED) {
+		dump_maps();
+		printf("Error:2: mmap() succeeded when it shouldn't have\n");
+		return 1;
+	}
+
+	/*
+	 * Overlap end of existing mapping:
+	 *   base |  free  |
+	 *     +1 | mapped |
+	 *     +2 | mapped |
+	 *     +3 | mapped | new
+	 *     +4 |  free  | new
+	 */
+	errno = 0;
+	addr = BASE_ADDRESS + (3 * page_size);
+	size = 2 * page_size;
+	p = mmap((void *)addr, size, PROT_NONE, flags, -1, 0);
+	printf("mmap() @ 0x%lx-0x%lx p=%p result=%m\n", addr, addr + size, p);
+
+	if (p != MAP_FAILED) {
+		dump_maps();
+		printf("Error:3: mmap() succeeded when it shouldn't have\n");
+		return 1;
+	}
+
+	/*
+	 * Overlap start of existing mapping:
+	 *   base |  free  | new
+	 *     +1 | mapped | new
+	 *     +2 | mapped |
+	 *     +3 | mapped |
+	 *     +4 |  free  |
+	 */
+	errno = 0;
+	addr = BASE_ADDRESS;
+	size = 2 * page_size;
+	p = mmap((void *)addr, size, PROT_NONE, flags, -1, 0);
+	printf("mmap() @ 0x%lx-0x%lx p=%p result=%m\n", addr, addr + size, p);
+
+	if (p != MAP_FAILED) {
+		dump_maps();
+		printf("Error:4: mmap() succeeded when it shouldn't have\n");
+		return 1;
+	}
+
+	/*
+	 * Adjacent to start of existing mapping:
+	 *   base |  free  | new
+	 *     +1 | mapped |
+	 *     +2 | mapped |
+	 *     +3 | mapped |
+	 *     +4 |  free  |
+	 */
+	errno = 0;
+	addr = BASE_ADDRESS;
+	size = page_size;
+	p = mmap((void *)addr, size, PROT_NONE, flags, -1, 0);
+	printf("mmap() @ 0x%lx-0x%lx p=%p result=%m\n", addr, addr + size, p);
+
+	if (p == MAP_FAILED) {
+		dump_maps();
+		printf("Error:5: mmap() failed when it shouldn't have\n");
+		return 1;
+	}
+
+	/*
+	 * Adjacent to end of existing mapping:
+	 *   base |  free  |
+	 *     +1 | mapped |
+	 *     +2 | mapped |
+	 *     +3 | mapped |
+	 *     +4 |  free  |  new
+	 */
+	errno = 0;
+	addr = BASE_ADDRESS + (4 * page_size);
+	size = page_size;
+	p = mmap((void *)addr, size, PROT_NONE, flags, -1, 0);
+	printf("mmap() @ 0x%lx-0x%lx p=%p result=%m\n", addr, addr + size, p);
+
+	if (p == MAP_FAILED) {
+		dump_maps();
+		printf("Error:6: mmap() failed when it shouldn't have\n");
+		return 1;
+	}
+
+	addr = BASE_ADDRESS;
+	size = 5 * page_size;
+	if (munmap((void *)addr, size) != 0) {
+		dump_maps();
+		printf("Error: munmap failed!?\n");
+		return 1;
+	}
+	printf("unmap() successful\n");
+
+	printf("OK\n");
+	return 0;
+}