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Strictly memwipe_check() for magic only in the affected buffer

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Passing back the buffer address we memwipe() is not ideal, as it could, in
theory, change the behavior of the compiler and not-optimize memwipe(). But
as checking a larger stack is very difficult for different architectures
and compilers, we do it nonetheless for now.
This commit is contained in:
Martin Willi
2013-06-05 15:02:18 +02:00
parent c480b5f458
commit bc1c92c9e9
1 changed files with 8 additions and 25 deletions
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src/libstrongswan/library.c
+8 -25
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@@ -155,21 +155,15 @@ static bool equals(char *a, char *b)
*/ */
#define MEMWIPE_WIPE_WORDS 16 #define MEMWIPE_WIPE_WORDS 16
/**
* Number of words we check stack for memwiped magic
*/
#define MEMWIPE_CHECK_WORDS (MEMWIPE_WIPE_WORDS * 2)
/** /**
* Write magic to memory, and try to clear it with memwipe() * Write magic to memory, and try to clear it with memwipe()
*/ */
__attribute__((noinline)) __attribute__((noinline))
static void do_magic(int *magic, int **stack) static void do_magic(int *magic, int **out)
{ {
int buf[MEMWIPE_WIPE_WORDS], i; int buf[MEMWIPE_WIPE_WORDS], i;
/* tell caller where callee stack is (but don't point to buf) */ *out = buf;
*stack = &i;
for (i = 0; i < countof(buf); i++) for (i = 0; i < countof(buf); i++)
{ {
buf[i] = *magic; buf[i] = *magic;
@@ -185,27 +179,16 @@ static void do_magic(int *magic, int **stack)
*/ */
static bool check_memwipe() static bool check_memwipe()
{ {
int magic = 0xCAFEBABE, *ptr, *deeper, i, stackdir = 1; int magic = 0xCAFEBABE, *buf, i;
do_magic(&magic, &deeper); do_magic(&magic, &buf);
ptr = &magic; for (i = 0; i < MEMWIPE_WIPE_WORDS; i++)
if (deeper < ptr)
{ /* stack grows down */
stackdir = -1;
}
for (i = 0; i < MEMWIPE_CHECK_WORDS; i++)
{ {
ptr = ptr + stackdir; if (buf[i] == magic)
if (*ptr == magic)
{ {
ptr = &magic + stackdir; DBG1(DBG_LIB, "memwipe() check failed: stackdir: %b",
if (stackdir == -1) buf, MEMWIPE_WIPE_WORDS * sizeof(int));
{
ptr -= MEMWIPE_CHECK_WORDS;
}
DBG1(DBG_LIB, "memwipe() check failed: stackdir: %d %b",
stackdir, ptr, (u_int)(MEMWIPE_CHECK_WORDS * sizeof(int)));
return FALSE; return FALSE;
} }
} }