--- /dev/null
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Tests for mremap w/ MREMAP_DONTUNMAP.
+ *
+ * Copyright 2020, Brian Geffon <bgeffon@google.com>
+ */
+#define _GNU_SOURCE
+#include <sys/mman.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "../kselftest.h"
+
+#ifndef MREMAP_DONTUNMAP
+#define MREMAP_DONTUNMAP 4
+#endif
+
+unsigned long page_size;
+char *page_buffer;
+
+static void dump_maps(void)
+{
+ char cmd[32];
+
+ snprintf(cmd, sizeof(cmd), "cat /proc/%d/maps", getpid());
+ system(cmd);
+}
+
+#define BUG_ON(condition, description) \
+ do { \
+ if (condition) { \
+ fprintf(stderr, "[FAIL]\t%s():%d\t%s:%s\n", __func__, \
+ __LINE__, (description), strerror(errno)); \
+ dump_maps(); \
+ exit(1); \
+ } \
+ } while (0)
+
+// Try a simple operation for to "test" for kernel support this prevents
+// reporting tests as failed when it's run on an older kernel.
+static int kernel_support_for_mremap_dontunmap()
+{
+ int ret = 0;
+ unsigned long num_pages = 1;
+ void *source_mapping = mmap(NULL, num_pages * page_size, PROT_NONE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(source_mapping == MAP_FAILED, "mmap");
+
+ // This simple remap should only fail if MREMAP_DONTUNMAP isn't
+ // supported.
+ void *dest_mapping =
+ mremap(source_mapping, num_pages * page_size, num_pages * page_size,
+ MREMAP_DONTUNMAP | MREMAP_MAYMOVE, 0);
+ if (dest_mapping == MAP_FAILED) {
+ ret = errno;
+ } else {
+ BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
+ "unable to unmap destination mapping");
+ }
+
+ BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
+ "unable to unmap source mapping");
+ return ret;
+}
+
+// This helper will just validate that an entire mapping contains the expected
+// byte.
+static int check_region_contains_byte(void *addr, unsigned long size, char byte)
+{
+ BUG_ON(size & (page_size - 1),
+ "check_region_contains_byte expects page multiples");
+ BUG_ON((unsigned long)addr & (page_size - 1),
+ "check_region_contains_byte expects page alignment");
+
+ memset(page_buffer, byte, page_size);
+
+ unsigned long num_pages = size / page_size;
+ unsigned long i;
+
+ // Compare each page checking that it contains our expected byte.
+ for (i = 0; i < num_pages; ++i) {
+ int ret =
+ memcmp(addr + (i * page_size), page_buffer, page_size);
+ if (ret) {
+ return ret;
+ }
+ }
+
+ return 0;
+}
+
+// this test validates that MREMAP_DONTUNMAP moves the pagetables while leaving
+// the source mapping mapped.
+static void mremap_dontunmap_simple()
+{
+ unsigned long num_pages = 5;
+
+ void *source_mapping =
+ mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(source_mapping == MAP_FAILED, "mmap");
+
+ memset(source_mapping, 'a', num_pages * page_size);
+
+ // Try to just move the whole mapping anywhere (not fixed).
+ void *dest_mapping =
+ mremap(source_mapping, num_pages * page_size, num_pages * page_size,
+ MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
+ BUG_ON(dest_mapping == MAP_FAILED, "mremap");
+
+ // Validate that the pages have been moved, we know they were moved if
+ // the dest_mapping contains a's.
+ BUG_ON(check_region_contains_byte
+ (dest_mapping, num_pages * page_size, 'a') != 0,
+ "pages did not migrate");
+ BUG_ON(check_region_contains_byte
+ (source_mapping, num_pages * page_size, 0) != 0,
+ "source should have no ptes");
+
+ BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
+ "unable to unmap destination mapping");
+ BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
+ "unable to unmap source mapping");
+}
+
+// This test validates MREMAP_DONTUNMAP will move page tables to a specific
+// destination using MREMAP_FIXED, also while validating that the source
+// remains intact.
+static void mremap_dontunmap_simple_fixed()
+{
+ unsigned long num_pages = 5;
+
+ // Since we want to guarantee that we can remap to a point, we will
+ // create a mapping up front.
+ void *dest_mapping =
+ mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(dest_mapping == MAP_FAILED, "mmap");
+ memset(dest_mapping, 'X', num_pages * page_size);
+
+ void *source_mapping =
+ mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(source_mapping == MAP_FAILED, "mmap");
+ memset(source_mapping, 'a', num_pages * page_size);
+
+ void *remapped_mapping =
+ mremap(source_mapping, num_pages * page_size, num_pages * page_size,
+ MREMAP_FIXED | MREMAP_DONTUNMAP | MREMAP_MAYMOVE,
+ dest_mapping);
+ BUG_ON(remapped_mapping == MAP_FAILED, "mremap");
+ BUG_ON(remapped_mapping != dest_mapping,
+ "mremap should have placed the remapped mapping at dest_mapping");
+
+ // The dest mapping will have been unmap by mremap so we expect the Xs
+ // to be gone and replaced with a's.
+ BUG_ON(check_region_contains_byte
+ (dest_mapping, num_pages * page_size, 'a') != 0,
+ "pages did not migrate");
+
+ // And the source mapping will have had its ptes dropped.
+ BUG_ON(check_region_contains_byte
+ (source_mapping, num_pages * page_size, 0) != 0,
+ "source should have no ptes");
+
+ BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
+ "unable to unmap destination mapping");
+ BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
+ "unable to unmap source mapping");
+}
+
+// This test validates that we can MREMAP_DONTUNMAP for a portion of an
+// existing mapping.
+static void mremap_dontunmap_partial_mapping()
+{
+ /*
+ * source mapping:
+ * --------------
+ * | aaaaaaaaaa |
+ * --------------
+ * to become:
+ * --------------
+ * | aaaaa00000 |
+ * --------------
+ * With the destination mapping containing 5 pages of As.
+ * ---------
+ * | aaaaa |
+ * ---------
+ */
+ unsigned long num_pages = 10;
+ void *source_mapping =
+ mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(source_mapping == MAP_FAILED, "mmap");
+ memset(source_mapping, 'a', num_pages * page_size);
+
+ // We will grab the last 5 pages of the source and move them.
+ void *dest_mapping =
+ mremap(source_mapping + (5 * page_size), 5 * page_size,
+ 5 * page_size,
+ MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
+ BUG_ON(dest_mapping == MAP_FAILED, "mremap");
+
+ // We expect the first 5 pages of the source to contain a's and the
+ // final 5 pages to contain zeros.
+ BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 'a') !=
+ 0, "first 5 pages of source should have original pages");
+ BUG_ON(check_region_contains_byte
+ (source_mapping + (5 * page_size), 5 * page_size, 0) != 0,
+ "final 5 pages of source should have no ptes");
+
+ // Finally we expect the destination to have 5 pages worth of a's.
+ BUG_ON(check_region_contains_byte(dest_mapping, 5 * page_size, 'a') !=
+ 0, "dest mapping should contain ptes from the source");
+
+ BUG_ON(munmap(dest_mapping, 5 * page_size) == -1,
+ "unable to unmap destination mapping");
+ BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
+ "unable to unmap source mapping");
+}
+
+// This test validates that we can remap over only a portion of a mapping.
+static void mremap_dontunmap_partial_mapping_overwrite(void)
+{
+ /*
+ * source mapping:
+ * ---------
+ * |aaaaa|
+ * ---------
+ * dest mapping initially:
+ * -----------
+ * |XXXXXXXXXX|
+ * ------------
+ * Source to become:
+ * ---------
+ * |00000|
+ * ---------
+ * With the destination mapping containing 5 pages of As.
+ * ------------
+ * |aaaaaXXXXX|
+ * ------------
+ */
+ void *source_mapping =
+ mmap(NULL, 5 * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(source_mapping == MAP_FAILED, "mmap");
+ memset(source_mapping, 'a', 5 * page_size);
+
+ void *dest_mapping =
+ mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(dest_mapping == MAP_FAILED, "mmap");
+ memset(dest_mapping, 'X', 10 * page_size);
+
+ // We will grab the last 5 pages of the source and move them.
+ void *remapped_mapping =
+ mremap(source_mapping, 5 * page_size,
+ 5 * page_size,
+ MREMAP_DONTUNMAP | MREMAP_MAYMOVE | MREMAP_FIXED, dest_mapping);
+ BUG_ON(dest_mapping == MAP_FAILED, "mremap");
+ BUG_ON(dest_mapping != remapped_mapping, "expected to remap to dest_mapping");
+
+ BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 0) !=
+ 0, "first 5 pages of source should have no ptes");
+
+ // Finally we expect the destination to have 5 pages worth of a's.
+ BUG_ON(check_region_contains_byte(dest_mapping, 5 * page_size, 'a') != 0,
+ "dest mapping should contain ptes from the source");
+
+ // Finally the last 5 pages shouldn't have been touched.
+ BUG_ON(check_region_contains_byte(dest_mapping + (5 * page_size),
+ 5 * page_size, 'X') != 0,
+ "dest mapping should have retained the last 5 pages");
+
+ BUG_ON(munmap(dest_mapping, 10 * page_size) == -1,
+ "unable to unmap destination mapping");
+ BUG_ON(munmap(source_mapping, 5 * page_size) == -1,
+ "unable to unmap source mapping");
+}
+
+int main(void)
+{
+ page_size = sysconf(_SC_PAGE_SIZE);
+
+ // test for kernel support for MREMAP_DONTUNMAP skipping the test if
+ // not.
+ if (kernel_support_for_mremap_dontunmap() != 0) {
+ printf("No kernel support for MREMAP_DONTUNMAP\n");
+ return KSFT_SKIP;
+ }
+
+ // Keep a page sized buffer around for when we need it.
+ page_buffer =
+ mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(page_buffer == MAP_FAILED, "unable to mmap a page.");
+
+ mremap_dontunmap_simple();
+ mremap_dontunmap_simple_fixed();
+ mremap_dontunmap_partial_mapping();
+ mremap_dontunmap_partial_mapping_overwrite();
+
+ BUG_ON(munmap(page_buffer, page_size) == -1,
+ "unable to unmap page buffer");
+
+ printf("OK\n");
+ return 0;
+}
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