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/* Test of explicit_bzero() function.
Copyright (C) 2020-2021 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Written by Bruno Haible <bruno@clisp.org>, 2020. */
#include <config.h>
/* Specification. */
#include <string.h>
#include "signature.h"
SIGNATURE_CHECK (explicit_bzero, void, (void *, size_t));
#include <stdbool.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include "vma-iter.h"
#include "macros.h"
/* Suppress GCC warning that do_secret_stuff (2) reads uninitialized
local storage. */
#if 4 < __GNUC__ + (3 <= __GNUC_MINOR__)
# pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
#endif
#define SECRET "xyzzy1729"
#define SECRET_SIZE 9
static char zero[SECRET_SIZE] = { 0 };
/* Enable this to verify that the test is effective. */
#if 0
# define explicit_bzero(a, n) memset (a, '\0', n)
#endif
/* =================== Verify operation on static memory =================== */
static char stbuf[SECRET_SIZE];
static void
test_static (void)
{
memcpy (stbuf, SECRET, SECRET_SIZE);
explicit_bzero (stbuf, SECRET_SIZE);
ASSERT (memcmp (zero, stbuf, SECRET_SIZE) == 0);
}
/* =============== Verify operation on heap-allocated memory =============== */
/* Test whether an address range is mapped in memory. */
#if VMA_ITERATE_SUPPORTED
struct locals
{
uintptr_t range_start;
uintptr_t range_end;
};
static int
vma_iterate_callback (void *data, uintptr_t start, uintptr_t end,
unsigned int flags)
{
struct locals *lp = (struct locals *) data;
/* Remove from [range_start, range_end) the part at the beginning or at the
end that is covered by [start, end). */
if (start <= lp->range_start && end > lp->range_start)
lp->range_start = (end < lp->range_end ? end : lp->range_end);
if (start < lp->range_end && end >= lp->range_end)
lp->range_end = (start > lp->range_start ? start : lp->range_start);
return 0;
}
static bool
is_range_mapped (uintptr_t range_start, uintptr_t range_end)
{
struct locals l;
l.range_start = range_start;
l.range_end = range_end;
vma_iterate (vma_iterate_callback, &l);
return l.range_start == l.range_end;
}
#else
static bool
is_range_mapped (uintptr_t range_start, uintptr_t range_end)
{
return true;
}
#endif
static void
test_heap (void)
{
char *heapbuf = (char *) malloc (SECRET_SIZE);
uintptr_t addr = (uintptr_t) heapbuf;
memcpy (heapbuf, SECRET, SECRET_SIZE);
explicit_bzero (heapbuf, SECRET_SIZE);
free (heapbuf);
if (is_range_mapped (addr, addr + SECRET_SIZE))
{
/* some implementation could override freed memory by canaries so
compare against secret */
ASSERT (memcmp (heapbuf, SECRET, SECRET_SIZE) != 0);
printf ("test_heap: address range is still mapped after free().\n");
}
else
printf ("test_heap: address range is unmapped after free().\n");
}
/* =============== Verify operation on stack-allocated memory =============== */
/* There are two passes:
1. Put a secret in memory and invoke explicit_bzero on it.
2. Verify that the memory has been erased.
Implement them in the same function, so that they access the same memory
range on the stack. That way, the test verifies that the compiler
does not eliminate a call to explicit_bzero, even if data flow analysis
reveals that the stack area is dead at the end of the function. */
static int _GL_ATTRIBUTE_NOINLINE
do_secret_stuff (volatile int pass)
{
static char *last_stackbuf;
char stackbuf[SECRET_SIZE];
if (pass == 1)
{
memcpy (stackbuf, SECRET, SECRET_SIZE);
explicit_bzero (stackbuf, SECRET_SIZE);
last_stackbuf = stackbuf;
return 0;
}
else /* pass == 2 */
{
/* Use last_stackbuf here, because stackbuf may be allocated at a
different address than last_stackbuf. This can happen
when the compiler splits this function into different functions,
one for pass == 1 and one for pass != 1. */
return memcmp (zero, last_stackbuf, SECRET_SIZE) != 0;
}
}
static void
test_stack (void)
{
int count = 0;
int repeat;
for (repeat = 2 * 1000; repeat > 0; repeat--)
{
/* This odd way of writing two consecutive statements
do_secret_stuff (1);
count += do_secret_stuff (2);
ensures that the two do_secret_stuff calls are performed with the same
stack pointer value, on m68k. */
if ((repeat % 2) == 0)
do_secret_stuff (1);
else
count += do_secret_stuff (2);
}
/* If explicit_bzero works, count is near 0. (It may be > 0 if there were
some asynchronous signal invocations between the two calls of
do_secret_stuff.)
If explicit_bzero is optimized away by the compiler, count comes out as
approximately 1000. */
printf ("test_stack: count = %d\n", count);
ASSERT (count < 50);
}
/* ========================================================================== */
int
main ()
{
test_static ();
test_heap ();
test_stack ();
return 0;
}
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