Here is a test for memwipe.

It invokes undefined behavior, I'm afraid, since there's no other
c-legal way to test whether memwipe() works when we're not allowed to
look at it.

Closes ticket 15377.

changes/test-memwipe

+  o Testing:
+    - Add a test to verify that the compiler does not eliminate our
+      memwipe() implementation. Closes ticket 15377.

src/test/include.am

-TESTS += src/test/test src/test/test-slow
+TESTS += src/test/test src/test/test-slow src/test/test-memwipe
 
 noinst_PROGRAMS+= src/test/bench
 if UNITTESTS_ENABLED
 noinst_PROGRAMS+= \
 	src/test/test \
 	src/test/test-slow \
+	src/test/test-memwipe \
 	src/test/test-child \
 	src/test/test_workqueue
 endif
@@ -73,6 +74,9 @@ src_test_test_slow_SOURCES = \
 	src/test/testing_common.c \
 	src/ext/tinytest.c
 
+src_test_test_memwipe_SOURCES = \
+	src/test/test-memwipe.c
+
 
 src_test_test_CFLAGS = $(AM_CFLAGS) $(TEST_CFLAGS)
 
@@ -100,6 +104,11 @@ src_test_test_slow_CFLAGS = $(src_test_test_CFLAGS)
 src_test_test_slow_LDADD = $(src_test_test_LDADD)
 src_test_test_slow_LDFLAGS = $(src_test_test_LDFLAGS)
 
+src_test_test_memwipe_CPPFLAGS = $(src_test_test_CPPFLAGS)
+src_test_test_memwipe_CFLAGS = $(src_test_test_CFLAGS)
+src_test_test_memwipe_LDADD = $(src_test_test_LDADD)
+src_test_test_memwipe_LDFLAGS = $(src_test_test_LDFLAGS)
+
 src_test_bench_LDFLAGS = @TOR_LDFLAGS_zlib@ @TOR_LDFLAGS_openssl@ \
         @TOR_LDFLAGS_libevent@
 src_test_bench_LDADD = src/or/libtor.a src/common/libor.a \

src/test/test-memwipe.c

+#include <string.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <stdlib.h>
+
+#include "crypto.h"
+#include "compat.h"
+
+#undef MIN
+#define MIN(a,b) ( ((a)<(b)) ? (a) : (b) )
+
+static unsigned fill_a_buffer_memset(void) __attribute__((noinline));
+static unsigned fill_a_buffer_memwipe(void) __attribute__((noinline));
+static unsigned fill_a_buffer_nothing(void) __attribute__((noinline));
+static unsigned fill_heap_buffer_memset(void) __attribute__((noinline));
+static unsigned fill_heap_buffer_memwipe(void) __attribute__((noinline));
+static unsigned fill_heap_buffer_nothing(void) __attribute__((noinline));
+static unsigned check_a_buffer(void) __attribute__((noinline));
+
+const char *s = NULL;
+
+#define FILL_BUFFER_IMPL()                                              \
+  unsigned int i;                                                       \
+  unsigned sum = 0;                                                     \
+                                                                        \
+  /* Fill up a 1k buffer with a recognizable pattern. */                \
+  for (i = 0; i < 2048; i += strlen(s)) {                               \
+    memcpy(buf+i, s, MIN(strlen(s), 2048-i));                           \
+  }                                                                     \
+                                                                        \
+  /* Use the buffer as input to a computation so the above can't get */ \
+  /* optimized away. */                                                 \
+  for (i = 0; i < 2048; ++i) {                                          \
+    sum += (unsigned char)buf[i];                                       \
+  }
+
+static unsigned
+fill_a_buffer_memset(void)
+{
+  char buf[2048];
+  FILL_BUFFER_IMPL()
+  memset(buf, 0, sizeof(buf));
+  return sum;
+}
+
+static unsigned
+fill_a_buffer_memwipe(void)
+{
+  char buf[2048];
+  FILL_BUFFER_IMPL()
+  memwipe(buf, 0, sizeof(buf));
+  return sum;
+}
+
+static unsigned
+fill_a_buffer_nothing(void)
+{
+  char buf[2048];
+  FILL_BUFFER_IMPL()
+  return sum;
+}
+
+static INLINE int
+vmemeq(volatile char *a, const char *b, size_t n)
+{
+  while (n--) {
+    if (*a++ != *b++)
+      return 0;
+  }
+  return 1;
+}
+
+static unsigned
+check_a_buffer(void)
+{
+  unsigned int i;
+  volatile char buf[1024];
+  unsigned sum = 0;
+
+  /* See if this buffer has the string in it.
+
+     YES, THIS DOES INVOKE UNDEFINED BEHAVIOR BY READING FROM AN UNINITIALIZED
+     BUFFER.
+
+     If you know a better way to figure out whether the compiler eliminated
+     the memset/memwipe calls or not, please let me know.
+   */
+  for (i = 0; i < sizeof(buf); ++i) {
+    if (vmemeq(buf+i, s, strlen(s)))
+      ++sum;
+  }
+
+  return sum;
+}
+
+static char *heap_buf = NULL;
+
+static unsigned
+fill_heap_buffer_memset(void)
+{
+  char *buf = heap_buf = malloc(2048);
+  FILL_BUFFER_IMPL()
+  memset(buf, 0, 2048);
+  free(buf);
+  return sum;
+}
+
+static unsigned
+fill_heap_buffer_memwipe(void)
+{
+  char *buf = heap_buf = malloc(2048);
+  FILL_BUFFER_IMPL()
+  memwipe(buf, 0, 2048);
+  free(buf);
+  return sum;
+}
+
+static unsigned
+fill_heap_buffer_nothing(void)
+{
+  char *buf = heap_buf = malloc(2048);
+  FILL_BUFFER_IMPL()
+  free(buf);
+  return sum;
+}
+
+static unsigned
+check_heap_buffer(void)
+{
+  unsigned int i;
+  unsigned sum = 0;
+  volatile char *buf = heap_buf;
+
+  /* See if this buffer has the string in it.
+
+     YES, THIS DOES INVOKE UNDEFINED BEHAVIOR BY READING FROM A FREED BUFFER.
+
+     If you know a better way to figure out whether the compiler eliminated
+     the memset/memwipe calls or not, please let me know.
+   */
+  for (i = 0; i < sizeof(buf); ++i) {
+    if (vmemeq(buf+i, s, strlen(s)))
+      ++sum;
+  }
+
+  return sum;
+}
+
+static struct testcase {
+  const char *name;
+  unsigned (*fill_fn)(void);
+  unsigned (*check_fn)(void);
+} testcases[] = {
+  { "nil", fill_a_buffer_nothing, check_a_buffer },
+  { "nil-heap", fill_heap_buffer_nothing, check_heap_buffer },
+  { "memset", fill_a_buffer_memset, check_a_buffer },
+  { "memset-heap", fill_heap_buffer_memset, check_heap_buffer },
+  { "memwipe", fill_a_buffer_memwipe, check_a_buffer },
+  { "memwipe-heap", fill_heap_buffer_memwipe, check_heap_buffer },
+  { NULL, NULL, NULL }
+};
+
+int
+main(int argc, char **argv)
+{
+  unsigned x, x2;
+  int i;
+  int working = 1;
+  unsigned found[6];
+  (void) argc; (void) argv;
+
+  s = "squamous haberdasher gallimaufry";
+
+  memset(found, 0, sizeof(found));
+
+  for (i = 0; testcases[i].name; ++i) {
+    x = testcases[i].fill_fn();
+    found[i] = testcases[i].check_fn();
+
+    x2 = fill_a_buffer_nothing();
+
+    if (x != x2) {
+      working = 0;
+    }
+  }
+
+  if (!working || !found[0] || !found[1]) {
+    printf("It appears that this test case may not give you reliable "
+           "information. Sorry.\n");
+  }
+
+  if (!found[2] && !found[3]) {
+    printf("It appears that memset is good enough on this platform. Good.\n");
+  }
+
+  if (found[4] || found[5]) {
+    printf("ERROR: memwipe does not wipe data!\n");
+    return 1;
+  } else {
+    printf("OKAY: memwipe seems to work.");
+    return 0;
+  }
+}
+