string: Add string/tst-memmove-overflow, a test case for bug 25620

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>

string/Makefile

@@ -60,7 +60,7 @@ tests		:= tester inl-tester noinl-tester testcopy test-ffs	\
 		   bug-envz1 tst-strxfrm2 tst-endian tst-svc2		\
 		   tst-strtok_r bug-strcoll2 tst-cmp tst-xbzero-opt	\
 		   test-endian-types test-endian-file-scope		\
-		   test-endian-sign-conversion
+		   test-endian-sign-conversion tst-memmove-overflow
 
 # This test allocates a lot of memory and can run for a long time.
 xtests = tst-strcoll-overflow

string/tst-memmove-overflow.c

@@ -0,0 +1,155 @@
+/* Test for signed comparision bug in memmove (bug 25620).
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* This test shifts a memory region which is a bit larger than 2 GiB
+   by one byte.  In order to make it more likely that the memory
+   allocation succeeds on 32-bit systems, most of the allocation
+   consists of shared pages.  Only a portion at the start and end of
+   the allocation are unshared, and contain a specific non-repeating
+   bit pattern.  */
+
+#include <array_length.h>
+#include <libc-diag.h>
+#include <stdint.h>
+#include <string.h>
+#include <support/blob_repeat.h>
+#include <support/check.h>
+#include <support/xunistd.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#define TEST_MAIN
+#define TEST_NAME "memmove"
+#include "test-string.h"
+#include <support/test-driver.h>
+
+IMPL (memmove, 1)
+
+/* Size of the part of the allocation which is not shared, at the
+   start and the end of the overall allocation.  4 MiB.  */
+static const size_t unshared_size = 4U << 20;
+
+/* The allocation is 2 GiB plus 8 MiB.  This should work with all page
+   sizes that occur in practice.  */
+static const size_t allocation_size = (2U << 30) + 2 * unshared_size;
+
+/* Compute the expected byte at the given index.  This is used to
+   produce a non-repeating pattern.  */
+static inline unsigned char
+expected_value (size_t index)
+{
+  uint32_t randomized = 0x9e3779b9 * index; /* Based on golden ratio.  */
+  return randomized >> 25;	/* Result is in the range [0, 127].  */
+}
+
+static int
+test_main (void)
+{
+  test_init ();
+
+  FOR_EACH_IMPL (impl, 0)
+    {
+      printf ("info: testing %s\n", impl->name);
+
+      /* Check that the allocation sizes are multiples of the page
+	 size.  */
+      TEST_COMPARE (allocation_size % xsysconf (_SC_PAGESIZE), 0);
+      TEST_COMPARE (unshared_size % xsysconf (_SC_PAGESIZE), 0);
+
+      /* The repeating pattern has the MSB set in all bytes.  */
+      unsigned char repeating_pattern[128];
+      for (unsigned int i = 0; i < array_length (repeating_pattern); ++i)
+	repeating_pattern[i] = 0x80 | i;
+
+      struct support_blob_repeat repeat
+	= support_blob_repeat_allocate_shared (repeating_pattern,
+					       sizeof (repeating_pattern),
+					       (allocation_size
+						/ sizeof (repeating_pattern)));
+      if (repeat.start == NULL)
+	FAIL_UNSUPPORTED ("repeated blob allocation failed: %m");
+      TEST_COMPARE (repeat.size, allocation_size);
+
+      /* Unshared the start and the end of the allocation.  */
+      unsigned char *start = repeat.start;
+      xmmap (start, unshared_size,
+	     PROT_READ | PROT_WRITE,
+	     MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1);
+      xmmap (start + allocation_size - unshared_size, unshared_size,
+	     PROT_READ | PROT_WRITE,
+	     MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1);
+
+      /* Initialize the non-repeating pattern.  */
+      for (size_t i = 0; i < unshared_size; ++i)
+	start[i] = expected_value (i);
+      for (size_t i = allocation_size - unshared_size; i < allocation_size;
+	   ++i)
+	start[i] = expected_value (i);
+
+      /* Make sure that there was really no sharing.  */
+      asm volatile ("" ::: "memory");
+      for (size_t i = 0; i < unshared_size; ++i)
+	TEST_COMPARE (start[i], expected_value (i));
+      for (size_t i = allocation_size - unshared_size; i < allocation_size;
+	   ++i)
+	TEST_COMPARE (start[i], expected_value (i));
+
+      /* Used for a nicer error diagnostic using
+	 TEST_COMPARE_BLOB.  */
+      unsigned char expected_start[128];
+      memcpy (expected_start, start + 1, sizeof (expected_start));
+      unsigned char expected_end[128];
+      memcpy (expected_end,
+	      start + allocation_size - sizeof (expected_end),
+	      sizeof (expected_end));
+
+      /* Move the entire allocation forward by one byte.  */
+      DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (8, 0)
+      /* GCC 8 warns about string function argument overflows.  */
+      DIAG_IGNORE_NEEDS_COMMENT (8, "-Warray-bounds");
+      DIAG_IGNORE_NEEDS_COMMENT (8, "-Wstringop-overflow");
+#endif
+      memmove (start, start + 1, allocation_size - 1);
+      DIAG_POP_NEEDS_COMMENT;
+
+      /* Check that the unshared of the memory region have been
+	 shifted as expected.  The TEST_COMPARE_BLOB checks are
+	 redundant, but produce nicer diagnostics.  */
+      asm volatile ("" ::: "memory");
+      TEST_COMPARE_BLOB (expected_start, sizeof (expected_start),
+			 start, sizeof (expected_start));
+      TEST_COMPARE_BLOB (expected_end, sizeof (expected_end),
+			 start + allocation_size - sizeof (expected_end) - 1,
+			 sizeof (expected_end));
+      for (size_t i = 0; i < unshared_size - 1; ++i)
+	TEST_COMPARE (start[i], expected_value (i + 1));
+      /* The gap between the checked start and end area of the mapping
+	 has shared mappings at unspecified boundaries, so do not
+	 check the expected values in the middle.  */
+      for (size_t i = allocation_size - unshared_size; i < allocation_size - 1;
+	   ++i)
+	TEST_COMPARE (start[i], expected_value (i + 1));
+
+      support_blob_repeat_free (&repeat);
+    }
+
+  return 0;
+}
+
+#include <support/test-driver.c>