putty/misc.c

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include "putty.h"

/*
 * My own versions of malloc, realloc and free. Because I want
 * malloc and realloc to bomb out and exit the program if they run
 * out of memory, realloc to reliably call malloc if passed a NULL
 * pointer, and free to reliably do nothing if passed a NULL
 * pointer. We can also put trace printouts in, if we need to; and
 * we can also replace the allocator with an ElectricFence-like
 * one.
 */

#ifdef MINEFIELD
/*
 * Minefield - a Windows equivalent for Electric Fence
 */

#define PAGESIZE 4096

/*
 * Design:
 * 
 * We start by reserving as much virtual address space as Windows
 * will sensibly (or not sensibly) let us have. We flag it all as
 * invalid memory.
 * 
 * Any allocation attempt is satisfied by committing one or more
 * pages, with an uncommitted page on either side. The returned
 * memory region is jammed up against the _end_ of the pages.
 * 
 * Freeing anything causes instantaneous decommitment of the pages
 * involved, so stale pointers are caught as soon as possible.
 */

static int minefield_initialised = 0;
static void *minefield_region = NULL;
static long minefield_size = 0;
static long minefield_npages = 0;
static long minefield_curpos = 0;
static unsigned short *minefield_admin = NULL;
static void *minefield_pages = NULL;

static void minefield_admin_hide(int hide) {
    int access = hide ? PAGE_NOACCESS : PAGE_READWRITE;
    VirtualProtect(minefield_admin, minefield_npages*2, access, NULL);
}

static void minefield_init(void) {
    int size;
    int admin_size;
    int i;

    for (size = 0x40000000; size > 0; size = ((size >> 3) * 7) &~ 0xFFF) {
        minefield_region = VirtualAlloc(NULL, size,
                                        MEM_RESERVE, PAGE_NOACCESS);
        if (minefield_region)
            break;
    }
    minefield_size = size;

    /*
     * Firstly, allocate a section of that to be the admin block.
     * We'll need a two-byte field for each page.
     */
    minefield_admin = minefield_region;
    minefield_npages = minefield_size / PAGESIZE;
    admin_size = (minefield_npages * 2 + PAGESIZE-1) &~ (PAGESIZE-1);
    minefield_npages = (minefield_size - admin_size) / PAGESIZE;
    minefield_pages = (char *)minefield_region + admin_size;

    /*
     * Commit the admin region.
     */
    VirtualAlloc(minefield_admin, minefield_npages * 2,
                 MEM_COMMIT, PAGE_READWRITE);

    /*
     * Mark all pages as unused (0xFFFF).
     */
    for (i = 0; i < minefield_npages; i++)
        minefield_admin[i] = 0xFFFF;

    /*
     * Hide the admin region.
     */
    minefield_admin_hide(1);

    minefield_initialised = 1;
}

static void minefield_bomb(void) {
    div(1, *(int*)minefield_pages);
}

static void *minefield_alloc(int size) {
    int npages;
    int pos, lim, region_end, region_start;
    int start;
    int i;

    npages = (size + PAGESIZE-1) / PAGESIZE;

    minefield_admin_hide(0);

    /*
     * Search from current position until we find a contiguous
     * bunch of npages+2 unused pages.
     */
    pos = minefield_curpos;
    lim = minefield_npages;
    while (1) {
        /* Skip over used pages. */
        while (pos < lim && minefield_admin[pos] != 0xFFFF)
            pos++;
        /* Count unused pages. */
        start = pos;
        while (pos < lim && pos - start < npages+2 &&
               minefield_admin[pos] == 0xFFFF)
            pos++;
        if (pos - start == npages+2)
            break;
        /* If we've reached the limit, reset the limit or stop. */
        if (pos >= lim) {
            if (lim == minefield_npages) {
                /* go round and start again at zero */
                lim = minefield_curpos;
                pos = 0;
            } else {
                minefield_admin_hide(1);
                return NULL;
            }
        }
    }

    minefield_curpos = pos-1;

    /*
     * We have npages+2 unused pages starting at start. We leave
     * the first and last of these alone and use the rest.
     */
    region_end = (start + npages+1) * PAGESIZE;
    region_start = region_end - size;
    /* FIXME: could align here if we wanted */

    /*
     * Update the admin region.
     */
    for (i = start + 2; i < start + npages-1; i++)
        minefield_admin[i] = 0xFFFE;   /* used but no region starts here */
    minefield_admin[start+1] = region_start % PAGESIZE;

    minefield_admin_hide(1);

    VirtualAlloc((char *)minefield_pages + region_start, size,
                 MEM_COMMIT, PAGE_READWRITE);
    return (char *)minefield_pages + region_start;
}

static void minefield_free(void *ptr) {
    int region_start, i, j;

    minefield_admin_hide(0);

    region_start = (char *)ptr - (char *)minefield_pages;
    i = region_start / PAGESIZE;
    if (i < 0 || i >= minefield_npages ||
        minefield_admin[i] != region_start % PAGESIZE)
        minefield_bomb();
    for (j = i; j < minefield_npages && minefield_admin[j] != 0xFFFF; j++) {
        minefield_admin[j] = 0xFFFF;
    }

    VirtualFree(ptr, j*PAGESIZE - region_start, MEM_DECOMMIT);

    minefield_admin_hide(1);
}

static int minefield_get_size(void *ptr) {
    int region_start, i, j;

    minefield_admin_hide(0);

    region_start = (char *)ptr - (char *)minefield_pages;
    i = region_start / PAGESIZE;
    if (i < 0 || i >= minefield_npages ||
        minefield_admin[i] != region_start % PAGESIZE)
        minefield_bomb();
    for (j = i; j < minefield_npages && minefield_admin[j] != 0xFFFF; j++);

    minefield_admin_hide(1);

    return j*PAGESIZE - region_start;
}

static void *minefield_c_malloc(size_t size) {
    if (!minefield_initialised) minefield_init();
    return minefield_alloc(size);
}

static void minefield_c_free(void *p) {
    if (!minefield_initialised) minefield_init();
    minefield_free(p);
}

/*
 * realloc _always_ moves the chunk, for rapid detection of code
 * that assumes it won't.
 */
static void *minefield_c_realloc(void *p, size_t size) {
    size_t oldsize;
    void *q;
    if (!minefield_initialised) minefield_init();
    q = minefield_alloc(size);
    oldsize = minefield_get_size(p);
    memcpy(q, p, (oldsize < size ? oldsize : size));
    minefield_free(p);
    return q;
}

#endif /* MINEFIELD */

#ifdef MALLOC_LOG
static FILE *fp = NULL;

void mlog(char *file, int line) {
    if (!fp) {
	fp = fopen("putty_mem.log", "w");
	setvbuf(fp, NULL, _IONBF, BUFSIZ);
    }
    if (fp)
	fprintf (fp, "%s:%d: ", file, line);
}
#endif

void *safemalloc(size_t size) {
    void *p;
#ifdef MINEFIELD
    p = minefield_c_malloc (size);
#else
    p = malloc (size);
#endif
    if (!p) {
	MessageBox(NULL, "Out of memory!", "PuTTY Fatal Error",
		   MB_SYSTEMMODAL | MB_ICONERROR | MB_OK);
	exit(1);
    }
#ifdef MALLOC_LOG
    if (fp)
	fprintf(fp, "malloc(%d) returns %p\n", size, p);
#endif
    return p;
}

void *saferealloc(void *ptr, size_t size) {
    void *p;
    if (!ptr) {
#ifdef MINEFIELD
	p = minefield_c_malloc (size);
#else
	p = malloc (size);
#endif
    } else {
#ifdef MINEFIELD
	p = minefield_c_realloc (ptr, size);
#else
	p = realloc (ptr, size);
#endif
    }
    if (!p) {
	MessageBox(NULL, "Out of memory!", "PuTTY Fatal Error",
		   MB_SYSTEMMODAL | MB_ICONERROR | MB_OK);
	exit(1);
    }
#ifdef MALLOC_LOG
    if (fp)
	fprintf(fp, "realloc(%p,%d) returns %p\n", ptr, size, p);
#endif
    return p;
}

void safefree(void *ptr) {
    if (ptr) {
#ifdef MALLOC_LOG
	if (fp)
	    fprintf(fp, "free(%p)\n", ptr);
#endif
#ifdef MINEFIELD
	minefield_c_free (ptr);
#else
	free (ptr);
#endif
    }
#ifdef MALLOC_LOG
    else if (fp)
	fprintf(fp, "freeing null pointer - no action taken\n");
#endif
}

#ifdef DEBUG
static FILE *debug_fp = NULL;
static int debug_got_console = 0;

void dprintf(char *fmt, ...) {
    char buf[2048];
    DWORD dw;
    va_list ap;

    if (!debug_got_console) {
	AllocConsole();
	debug_got_console = 1;
    }
    if (!debug_fp) {
	debug_fp = fopen("debug.log", "w");
    }

    va_start(ap, fmt);
    vsprintf(buf, fmt, ap);
    WriteFile(GetStdHandle(STD_OUTPUT_HANDLE), buf, strlen(buf), &dw, NULL);
    fputs(buf, debug_fp);
    fflush(debug_fp);
    va_end(ap);
}
#endif