The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/vm/memguard.c

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    1 /*-
    2  * Copyright (c) 2005, Bosko Milekic <bmilekic@FreeBSD.org>.
    3  * Copyright (c) 2010 Isilon Systems, Inc. (http://www.isilon.com/)
    4  * All rights reserved.
    5  *
    6  * Redistribution and use in source and binary forms, with or without
    7  * modification, are permitted provided that the following conditions
    8  * are met:
    9  * 1. Redistributions of source code must retain the above copyright
   10  *    notice unmodified, this list of conditions, and the following
   11  *    disclaimer.
   12  * 2. Redistributions in binary form must reproduce the above copyright
   13  *    notice, this list of conditions and the following disclaimer in the
   14  *    documentation and/or other materials provided with the distribution.
   15  *
   16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
   17  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   18  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   19  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
   20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   21  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   22  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   23  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   24  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   25  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   26  */
   27 
   28 #include <sys/cdefs.h>
   29 __FBSDID("$FreeBSD: releng/8.2/sys/vm/memguard.c 215743 2010-11-23 13:25:27Z zec $");
   30 
   31 /*
   32  * MemGuard is a simple replacement allocator for debugging only
   33  * which provides ElectricFence-style memory barrier protection on
   34  * objects being allocated, and is used to detect tampering-after-free
   35  * scenarios.
   36  *
   37  * See the memguard(9) man page for more information on using MemGuard.
   38  */
   39 
   40 #include "opt_vm.h"
   41 
   42 #include <sys/param.h>
   43 #include <sys/systm.h>
   44 #include <sys/kernel.h>
   45 #include <sys/types.h>
   46 #include <sys/queue.h>
   47 #include <sys/lock.h>
   48 #include <sys/mutex.h>
   49 #include <sys/malloc.h>
   50 #include <sys/sysctl.h>
   51 
   52 #include <vm/vm.h>
   53 #include <vm/uma.h>
   54 #include <vm/vm_param.h>
   55 #include <vm/vm_page.h>
   56 #include <vm/vm_map.h>
   57 #include <vm/vm_object.h>
   58 #include <vm/vm_extern.h>
   59 #include <vm/memguard.h>
   60 
   61 SYSCTL_NODE(_vm, OID_AUTO, memguard, CTLFLAG_RW, NULL, "MemGuard data");
   62 /*
   63  * The vm_memguard_divisor variable controls how much of kmem_map should be
   64  * reserved for MemGuard.
   65  */
   66 static u_int vm_memguard_divisor;
   67 SYSCTL_UINT(_vm_memguard, OID_AUTO, divisor, CTLFLAG_RDTUN,
   68     &vm_memguard_divisor,
   69     0, "(kmem_size/memguard_divisor) == memguard submap size");     
   70 
   71 /*
   72  * Short description (ks_shortdesc) of memory type to monitor.
   73  */
   74 static char vm_memguard_desc[128] = "";
   75 static struct malloc_type *vm_memguard_mtype = NULL;
   76 TUNABLE_STR("vm.memguard.desc", vm_memguard_desc, sizeof(vm_memguard_desc));
   77 static int
   78 memguard_sysctl_desc(SYSCTL_HANDLER_ARGS)
   79 {
   80         char desc[sizeof(vm_memguard_desc)];
   81         int error;
   82 
   83         strlcpy(desc, vm_memguard_desc, sizeof(desc));
   84         error = sysctl_handle_string(oidp, desc, sizeof(desc), req);
   85         if (error != 0 || req->newptr == NULL)
   86                 return (error);
   87 
   88         mtx_lock(&malloc_mtx);
   89         /*
   90          * If mtp is NULL, it will be initialized in memguard_cmp().
   91          */
   92         vm_memguard_mtype = malloc_desc2type(desc);
   93         strlcpy(vm_memguard_desc, desc, sizeof(vm_memguard_desc));
   94         mtx_unlock(&malloc_mtx);
   95         return (error);
   96 }
   97 SYSCTL_PROC(_vm_memguard, OID_AUTO, desc,
   98     CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 0,
   99     memguard_sysctl_desc, "A", "Short description of memory type to monitor");
  100 
  101 static vm_map_t memguard_map = NULL;
  102 static vm_offset_t memguard_cursor;
  103 static vm_size_t memguard_mapsize;
  104 static vm_size_t memguard_physlimit;
  105 static u_long memguard_wasted;
  106 static u_long memguard_wrap;
  107 static u_long memguard_succ;
  108 static u_long memguard_fail_kva;
  109 static u_long memguard_fail_pgs;
  110 
  111 SYSCTL_ULONG(_vm_memguard, OID_AUTO, cursor, CTLFLAG_RD,
  112     &memguard_cursor, 0, "MemGuard cursor");
  113 SYSCTL_ULONG(_vm_memguard, OID_AUTO, mapsize, CTLFLAG_RD,
  114     &memguard_mapsize, 0, "MemGuard private vm_map size");
  115 SYSCTL_ULONG(_vm_memguard, OID_AUTO, phys_limit, CTLFLAG_RD,
  116     &memguard_physlimit, 0, "Limit on MemGuard memory consumption");
  117 SYSCTL_ULONG(_vm_memguard, OID_AUTO, wasted, CTLFLAG_RD,
  118     &memguard_wasted, 0, "Excess memory used through page promotion");
  119 SYSCTL_ULONG(_vm_memguard, OID_AUTO, wrapcnt, CTLFLAG_RD,
  120     &memguard_wrap, 0, "MemGuard cursor wrap count");
  121 SYSCTL_ULONG(_vm_memguard, OID_AUTO, numalloc, CTLFLAG_RD,
  122     &memguard_succ, 0, "Count of successful MemGuard allocations");
  123 SYSCTL_ULONG(_vm_memguard, OID_AUTO, fail_kva, CTLFLAG_RD,
  124     &memguard_fail_kva, 0, "MemGuard failures due to lack of KVA");
  125 SYSCTL_ULONG(_vm_memguard, OID_AUTO, fail_pgs, CTLFLAG_RD,
  126     &memguard_fail_pgs, 0, "MemGuard failures due to lack of pages");
  127 
  128 #define MG_GUARD        0x001
  129 #define MG_ALLLARGE     0x002
  130 static int memguard_options = MG_GUARD;
  131 TUNABLE_INT("vm.memguard.options", &memguard_options);
  132 SYSCTL_INT(_vm_memguard, OID_AUTO, options, CTLFLAG_RW,
  133     &memguard_options, 0,
  134     "MemGuard options:\n"
  135     "\t0x001 - add guard pages around each allocation\n"
  136     "\t0x002 - always use MemGuard for allocations over a page");
  137 
  138 static u_int memguard_minsize;
  139 static u_long memguard_minsize_reject;
  140 SYSCTL_UINT(_vm_memguard, OID_AUTO, minsize, CTLFLAG_RW,
  141     &memguard_minsize, 0, "Minimum size for page promotion");
  142 SYSCTL_ULONG(_vm_memguard, OID_AUTO, minsize_reject, CTLFLAG_RD,
  143     &memguard_minsize_reject, 0, "# times rejected for size");
  144 
  145 static u_int memguard_frequency;
  146 static u_long memguard_frequency_hits;
  147 TUNABLE_INT("vm.memguard.frequency", &memguard_frequency);
  148 SYSCTL_UINT(_vm_memguard, OID_AUTO, frequency, CTLFLAG_RW,
  149     &memguard_frequency, 0, "Times in 100000 that MemGuard will randomly run");
  150 SYSCTL_ULONG(_vm_memguard, OID_AUTO, frequency_hits, CTLFLAG_RD,
  151     &memguard_frequency_hits, 0, "# times MemGuard randomly chose");
  152 
  153 
  154 /*
  155  * Return a fudged value to be used for vm_kmem_size for allocating
  156  * the kmem_map.  The memguard memory will be a submap.
  157  */
  158 unsigned long
  159 memguard_fudge(unsigned long km_size, unsigned long km_max)
  160 {
  161         u_long mem_pgs = cnt.v_page_count;
  162 
  163         vm_memguard_divisor = 10;
  164         TUNABLE_INT_FETCH("vm.memguard.divisor", &vm_memguard_divisor);
  165 
  166         /* Pick a conservative value if provided value sucks. */
  167         if ((vm_memguard_divisor <= 0) ||
  168             ((km_size / vm_memguard_divisor) == 0))
  169                 vm_memguard_divisor = 10;
  170         /*
  171          * Limit consumption of physical pages to
  172          * 1/vm_memguard_divisor of system memory.  If the KVA is
  173          * smaller than this then the KVA limit comes into play first.
  174          * This prevents memguard's page promotions from completely
  175          * using up memory, since most malloc(9) calls are sub-page.
  176          */
  177         memguard_physlimit = (mem_pgs / vm_memguard_divisor) * PAGE_SIZE;
  178         /*
  179          * We want as much KVA as we can take safely.  Use at most our
  180          * allotted fraction of kmem_max.  Limit this to twice the
  181          * physical memory to avoid using too much memory as pagetable
  182          * pages.
  183          */
  184         memguard_mapsize = km_max / vm_memguard_divisor;
  185         /* size must be multiple of PAGE_SIZE */
  186         memguard_mapsize = round_page(memguard_mapsize);
  187         if (memguard_mapsize / (2 * PAGE_SIZE) > mem_pgs)
  188                 memguard_mapsize = mem_pgs * 2 * PAGE_SIZE;
  189         if (km_size + memguard_mapsize > km_max)
  190                 return (km_max);
  191         return (km_size + memguard_mapsize);
  192 }
  193 
  194 /*
  195  * Initialize the MemGuard mock allocator.  All objects from MemGuard come
  196  * out of a single VM map (contiguous chunk of address space).
  197  */
  198 void
  199 memguard_init(vm_map_t parent_map)
  200 {
  201         vm_offset_t base, limit;
  202 
  203         memguard_map = kmem_suballoc(parent_map, &base, &limit,
  204             memguard_mapsize, FALSE);
  205         memguard_map->system_map = 1;
  206         KASSERT(memguard_mapsize == limit - base,
  207             ("Expected %lu, got %lu", (u_long)memguard_mapsize,
  208              (u_long)(limit - base)));
  209         memguard_cursor = base;
  210 
  211         printf("MEMGUARD DEBUGGING ALLOCATOR INITIALIZED:\n");
  212         printf("\tMEMGUARD map base: 0x%lx\n", (u_long)base);
  213         printf("\tMEMGUARD map limit: 0x%lx\n", (u_long)limit);
  214         printf("\tMEMGUARD map size: %jd KBytes\n",
  215             (uintmax_t)memguard_mapsize >> 10);
  216 }
  217 
  218 /*
  219  * Run things that can't be done as early as memguard_init().
  220  */
  221 static void
  222 memguard_sysinit(void)
  223 {
  224         struct sysctl_oid_list *parent;
  225 
  226         parent = SYSCTL_STATIC_CHILDREN(_vm_memguard);
  227 
  228         SYSCTL_ADD_ULONG(NULL, parent, OID_AUTO, "mapstart", CTLFLAG_RD,
  229             &memguard_map->min_offset, "MemGuard KVA base");
  230         SYSCTL_ADD_ULONG(NULL, parent, OID_AUTO, "maplimit", CTLFLAG_RD,
  231             &memguard_map->max_offset, "MemGuard KVA end");
  232         SYSCTL_ADD_ULONG(NULL, parent, OID_AUTO, "mapused", CTLFLAG_RD,
  233             &memguard_map->size, "MemGuard KVA used");
  234 }
  235 SYSINIT(memguard, SI_SUB_KLD, SI_ORDER_ANY, memguard_sysinit, NULL);
  236 
  237 /*
  238  * v2sizep() converts a virtual address of the first page allocated for
  239  * an item to a pointer to u_long recording the size of the original
  240  * allocation request.
  241  *
  242  * This routine is very similar to those defined by UMA in uma_int.h.
  243  * The difference is that this routine stores the originally allocated
  244  * size in one of the page's fields that is unused when the page is
  245  * wired rather than the object field, which is used.
  246  */
  247 static u_long *
  248 v2sizep(vm_offset_t va)
  249 {
  250         vm_paddr_t pa;
  251         struct vm_page *p;
  252 
  253         pa = pmap_kextract(va);
  254         if (pa == 0)
  255                 panic("MemGuard detected double-free of %p", (void *)va);
  256         p = PHYS_TO_VM_PAGE(pa);
  257         KASSERT(p->wire_count != 0 && p->queue == PQ_NONE,
  258             ("MEMGUARD: Expected wired page %p in vtomgfifo!", p));
  259         return ((u_long *)&p->pageq.tqe_next);
  260 }
  261 
  262 /*
  263  * Allocate a single object of specified size with specified flags
  264  * (either M_WAITOK or M_NOWAIT).
  265  */
  266 void *
  267 memguard_alloc(unsigned long req_size, int flags)
  268 {
  269         vm_offset_t addr;
  270         u_long size_p, size_v;
  271         int do_guard, rv;
  272 
  273         size_p = round_page(req_size);
  274         if (size_p == 0)
  275                 return (NULL);
  276         /*
  277          * To ensure there are holes on both sides of the allocation,
  278          * request 2 extra pages of KVA.  We will only actually add a
  279          * vm_map_entry and get pages for the original request.  Save
  280          * the value of memguard_options so we have a consistent
  281          * value.
  282          */
  283         size_v = size_p;
  284         do_guard = (memguard_options & MG_GUARD) != 0;
  285         if (do_guard)
  286                 size_v += 2 * PAGE_SIZE;
  287 
  288         vm_map_lock(memguard_map);
  289         /*
  290          * When we pass our memory limit, reject sub-page allocations.
  291          * Page-size and larger allocations will use the same amount
  292          * of physical memory whether we allocate or hand off to
  293          * uma_large_alloc(), so keep those.
  294          */
  295         if (memguard_map->size >= memguard_physlimit &&
  296             req_size < PAGE_SIZE) {
  297                 addr = (vm_offset_t)NULL;
  298                 memguard_fail_pgs++;
  299                 goto out;
  300         }
  301         /*
  302          * Keep a moving cursor so we don't recycle KVA as long as
  303          * possible.  It's not perfect, since we don't know in what
  304          * order previous allocations will be free'd, but it's simple
  305          * and fast, and requires O(1) additional storage if guard
  306          * pages are not used.
  307          *
  308          * XXX This scheme will lead to greater fragmentation of the
  309          * map, unless vm_map_findspace() is tweaked.
  310          */
  311         for (;;) {
  312                 rv = vm_map_findspace(memguard_map, memguard_cursor,
  313                     size_v, &addr);
  314                 if (rv == KERN_SUCCESS)
  315                         break;
  316                 /*
  317                  * The map has no space.  This may be due to
  318                  * fragmentation, or because the cursor is near the
  319                  * end of the map.
  320                  */
  321                 if (memguard_cursor == vm_map_min(memguard_map)) {
  322                         memguard_fail_kva++;
  323                         addr = (vm_offset_t)NULL;
  324                         goto out;
  325                 }
  326                 memguard_wrap++;
  327                 memguard_cursor = vm_map_min(memguard_map);
  328         }
  329         if (do_guard)
  330                 addr += PAGE_SIZE;
  331         rv = kmem_back(memguard_map, addr, size_p, flags);
  332         if (rv != KERN_SUCCESS) {
  333                 memguard_fail_pgs++;
  334                 addr = (vm_offset_t)NULL;
  335                 goto out;
  336         }
  337         memguard_cursor = addr + size_p;
  338         *v2sizep(trunc_page(addr)) = req_size;
  339         memguard_succ++;
  340         if (req_size < PAGE_SIZE) {
  341                 memguard_wasted += (PAGE_SIZE - req_size);
  342                 if (do_guard) {
  343                         /*
  344                          * Align the request to 16 bytes, and return
  345                          * an address near the end of the page, to
  346                          * better detect array overrun.
  347                          */
  348                         req_size = roundup2(req_size, 16);
  349                         addr += (PAGE_SIZE - req_size);
  350                 }
  351         }
  352 out:
  353         vm_map_unlock(memguard_map);
  354         return ((void *)addr);
  355 }
  356 
  357 int
  358 is_memguard_addr(void *addr)
  359 {
  360         vm_offset_t a = (vm_offset_t)(uintptr_t)addr;
  361 
  362         return (a >= memguard_map->min_offset && a < memguard_map->max_offset);
  363 }
  364 
  365 /*
  366  * Free specified single object.
  367  */
  368 void
  369 memguard_free(void *ptr)
  370 {
  371         vm_offset_t addr;
  372         u_long req_size, size;
  373         char *temp;
  374         int i;
  375 
  376         addr = trunc_page((uintptr_t)ptr);
  377         req_size = *v2sizep(addr);
  378         size = round_page(req_size);
  379 
  380         /*
  381          * Page should not be guarded right now, so force a write.
  382          * The purpose of this is to increase the likelihood of
  383          * catching a double-free, but not necessarily a
  384          * tamper-after-free (the second thread freeing might not
  385          * write before freeing, so this forces it to and,
  386          * subsequently, trigger a fault).
  387          */
  388         temp = ptr;
  389         for (i = 0; i < size; i += PAGE_SIZE)
  390                 temp[i] = 'M';
  391 
  392         /*
  393          * This requires carnal knowledge of the implementation of
  394          * kmem_free(), but since we've already replaced kmem_malloc()
  395          * above, it's not really any worse.  We want to use the
  396          * vm_map lock to serialize updates to memguard_wasted, since
  397          * we had the lock at increment.
  398          */
  399         vm_map_lock(memguard_map);
  400         if (req_size < PAGE_SIZE)
  401                 memguard_wasted -= (PAGE_SIZE - req_size);
  402         (void)vm_map_delete(memguard_map, addr, addr + size);
  403         vm_map_unlock(memguard_map);
  404 }
  405 
  406 /*
  407  * Re-allocate an allocation that was originally guarded.
  408  */
  409 void *
  410 memguard_realloc(void *addr, unsigned long size, struct malloc_type *mtp,
  411     int flags)
  412 {
  413         void *newaddr;
  414         u_long old_size;
  415 
  416         /*
  417          * Allocate the new block.  Force the allocation to be guarded
  418          * as the original may have been guarded through random
  419          * chance, and that should be preserved.
  420          */
  421         if ((newaddr = memguard_alloc(size, flags)) == NULL)
  422                 return (NULL);
  423 
  424         /* Copy over original contents. */
  425         old_size = *v2sizep(trunc_page((uintptr_t)addr));
  426         bcopy(addr, newaddr, min(size, old_size));
  427         memguard_free(addr);
  428         return (newaddr);
  429 }
  430 
  431 int
  432 memguard_cmp(struct malloc_type *mtp, unsigned long size)
  433 {
  434 
  435         if (size < memguard_minsize) {
  436                 memguard_minsize_reject++;
  437                 return (0);
  438         }
  439         if ((memguard_options & MG_ALLLARGE) != 0 && size >= PAGE_SIZE)
  440                 return (1);
  441         if (memguard_frequency > 0 &&
  442             (random() % 100000) < memguard_frequency) {
  443                 memguard_frequency_hits++;
  444                 return (1);
  445         }
  446 #if 1
  447         /*
  448          * The safest way of comparsion is to always compare short description
  449          * string of memory type, but it is also the slowest way.
  450          */
  451         return (strcmp(mtp->ks_shortdesc, vm_memguard_desc) == 0);
  452 #else
  453         /*
  454          * If we compare pointers, there are two possible problems:
  455          * 1. Memory type was unloaded and new memory type was allocated at the
  456          *    same address.
  457          * 2. Memory type was unloaded and loaded again, but allocated at a
  458          *    different address.
  459          */
  460         if (vm_memguard_mtype != NULL)
  461                 return (mtp == vm_memguard_mtype);
  462         if (strcmp(mtp->ks_shortdesc, vm_memguard_desc) == 0) {
  463                 vm_memguard_mtype = mtp;
  464                 return (1);
  465         }
  466         return (0);
  467 #endif
  468 }

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