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("$FreeBSD$");
   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 #include <sys/vmem.h>
   52 #include <sys/vmmeter.h>
   53 
   54 #include <vm/vm.h>
   55 #include <vm/uma.h>
   56 #include <vm/vm_param.h>
   57 #include <vm/vm_page.h>
   58 #include <vm/vm_map.h>
   59 #include <vm/vm_object.h>
   60 #include <vm/vm_kern.h>
   61 #include <vm/vm_extern.h>
   62 #include <vm/uma_int.h>
   63 #include <vm/memguard.h>
   64 
   65 static SYSCTL_NODE(_vm, OID_AUTO, memguard, CTLFLAG_RW, NULL, "MemGuard data");
   66 /*
   67  * The vm_memguard_divisor variable controls how much of kmem_map should be
   68  * reserved for MemGuard.
   69  */
   70 static u_int vm_memguard_divisor;
   71 SYSCTL_UINT(_vm_memguard, OID_AUTO, divisor, CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
   72     &vm_memguard_divisor,
   73     0, "(kmem_size/memguard_divisor) == memguard submap size");
   74 
   75 /*
   76  * Short description (ks_shortdesc) of memory type to monitor.
   77  */
   78 static char vm_memguard_desc[128] = "";
   79 static struct malloc_type *vm_memguard_mtype = NULL;
   80 TUNABLE_STR("vm.memguard.desc", vm_memguard_desc, sizeof(vm_memguard_desc));
   81 static int
   82 memguard_sysctl_desc(SYSCTL_HANDLER_ARGS)
   83 {
   84         char desc[sizeof(vm_memguard_desc)];
   85         int error;
   86 
   87         strlcpy(desc, vm_memguard_desc, sizeof(desc));
   88         error = sysctl_handle_string(oidp, desc, sizeof(desc), req);
   89         if (error != 0 || req->newptr == NULL)
   90                 return (error);
   91 
   92         mtx_lock(&malloc_mtx);
   93         /* If mtp is NULL, it will be initialized in memguard_cmp() */
   94         vm_memguard_mtype = malloc_desc2type(desc);
   95         strlcpy(vm_memguard_desc, desc, sizeof(vm_memguard_desc));
   96         mtx_unlock(&malloc_mtx);
   97         return (error);
   98 }
   99 SYSCTL_PROC(_vm_memguard, OID_AUTO, desc,
  100     CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 0,
  101     memguard_sysctl_desc, "A", "Short description of memory type to monitor");
  102 
  103 static vm_offset_t memguard_cursor;
  104 static vm_offset_t memguard_base;
  105 static vm_size_t memguard_mapsize;
  106 static vm_size_t memguard_physlimit;
  107 static u_long memguard_wasted;
  108 static u_long memguard_wrap;
  109 static u_long memguard_succ;
  110 static u_long memguard_fail_kva;
  111 static u_long memguard_fail_pgs;
  112 
  113 SYSCTL_ULONG(_vm_memguard, OID_AUTO, cursor, CTLFLAG_RD,
  114     &memguard_cursor, 0, "MemGuard cursor");
  115 SYSCTL_ULONG(_vm_memguard, OID_AUTO, mapsize, CTLFLAG_RD,
  116     &memguard_mapsize, 0, "MemGuard private arena size");
  117 SYSCTL_ULONG(_vm_memguard, OID_AUTO, phys_limit, CTLFLAG_RD,
  118     &memguard_physlimit, 0, "Limit on MemGuard memory consumption");
  119 SYSCTL_ULONG(_vm_memguard, OID_AUTO, wasted, CTLFLAG_RD,
  120     &memguard_wasted, 0, "Excess memory used through page promotion");
  121 SYSCTL_ULONG(_vm_memguard, OID_AUTO, wrapcnt, CTLFLAG_RD,
  122     &memguard_wrap, 0, "MemGuard cursor wrap count");
  123 SYSCTL_ULONG(_vm_memguard, OID_AUTO, numalloc, CTLFLAG_RD,
  124     &memguard_succ, 0, "Count of successful MemGuard allocations");
  125 SYSCTL_ULONG(_vm_memguard, OID_AUTO, fail_kva, CTLFLAG_RD,
  126     &memguard_fail_kva, 0, "MemGuard failures due to lack of KVA");
  127 SYSCTL_ULONG(_vm_memguard, OID_AUTO, fail_pgs, CTLFLAG_RD,
  128     &memguard_fail_pgs, 0, "MemGuard failures due to lack of pages");
  129 
  130 #define MG_GUARD_AROUND         0x001
  131 #define MG_GUARD_ALLLARGE       0x002
  132 #define MG_GUARD_NOFREE         0x004
  133 static int memguard_options = MG_GUARD_AROUND;
  134 SYSCTL_INT(_vm_memguard, OID_AUTO, options, CTLFLAG_RWTUN,
  135     &memguard_options, 0,
  136     "MemGuard options:\n"
  137     "\t0x001 - add guard pages around each allocation\n"
  138     "\t0x002 - always use MemGuard for allocations over a page\n"
  139     "\t0x004 - guard uma(9) zones with UMA_ZONE_NOFREE flag");
  140 
  141 static u_int memguard_minsize;
  142 static u_long memguard_minsize_reject;
  143 SYSCTL_UINT(_vm_memguard, OID_AUTO, minsize, CTLFLAG_RW,
  144     &memguard_minsize, 0, "Minimum size for page promotion");
  145 SYSCTL_ULONG(_vm_memguard, OID_AUTO, minsize_reject, CTLFLAG_RD,
  146     &memguard_minsize_reject, 0, "# times rejected for size");
  147 
  148 static u_int memguard_frequency;
  149 static u_long memguard_frequency_hits;
  150 SYSCTL_UINT(_vm_memguard, OID_AUTO, frequency, CTLFLAG_RWTUN,
  151     &memguard_frequency, 0, "Times in 100000 that MemGuard will randomly run");
  152 SYSCTL_ULONG(_vm_memguard, OID_AUTO, frequency_hits, CTLFLAG_RD,
  153     &memguard_frequency_hits, 0, "# times MemGuard randomly chose");
  154 
  155 
  156 /*
  157  * Return a fudged value to be used for vm_kmem_size for allocating
  158  * the kmem_map.  The memguard memory will be a submap.
  159  */
  160 unsigned long
  161 memguard_fudge(unsigned long km_size, const struct vm_map *parent_map)
  162 {
  163         u_long mem_pgs, parent_size;
  164 
  165         vm_memguard_divisor = 10;
  166         /* CTFLAG_RDTUN doesn't work during the early boot process. */
  167         TUNABLE_INT_FETCH("vm.memguard.divisor", &vm_memguard_divisor);
  168 
  169         parent_size = vm_map_max(parent_map) - vm_map_min(parent_map) +
  170             PAGE_SIZE;
  171         /* Pick a conservative value if provided value sucks. */
  172         if ((vm_memguard_divisor <= 0) ||
  173             ((parent_size / vm_memguard_divisor) == 0))
  174                 vm_memguard_divisor = 10;
  175         /*
  176          * Limit consumption of physical pages to
  177          * 1/vm_memguard_divisor of system memory.  If the KVA is
  178          * smaller than this then the KVA limit comes into play first.
  179          * This prevents memguard's page promotions from completely
  180          * using up memory, since most malloc(9) calls are sub-page.
  181          */
  182         mem_pgs = vm_cnt.v_page_count;
  183         memguard_physlimit = (mem_pgs / vm_memguard_divisor) * PAGE_SIZE;
  184         /*
  185          * We want as much KVA as we can take safely.  Use at most our
  186          * allotted fraction of the parent map's size.  Limit this to
  187          * twice the physical memory to avoid using too much memory as
  188          * pagetable pages (size must be multiple of PAGE_SIZE).
  189          */
  190         memguard_mapsize = round_page(parent_size / vm_memguard_divisor);
  191         if (memguard_mapsize / (2 * PAGE_SIZE) > mem_pgs)
  192                 memguard_mapsize = mem_pgs * 2 * PAGE_SIZE;
  193         if (km_size + memguard_mapsize > parent_size)
  194                 memguard_mapsize = 0;
  195         return (km_size + memguard_mapsize);
  196 }
  197 
  198 /*
  199  * Initialize the MemGuard mock allocator.  All objects from MemGuard come
  200  * out of a single VM map (contiguous chunk of address space).
  201  */
  202 void
  203 memguard_init(vmem_t *parent)
  204 {
  205         vm_offset_t base;
  206 
  207         vmem_alloc(parent, memguard_mapsize, M_BESTFIT | M_WAITOK, &base);
  208         vmem_init(memguard_arena, "memguard arena", base, memguard_mapsize,
  209             PAGE_SIZE, 0, M_WAITOK);
  210         memguard_cursor = base;
  211         memguard_base = base;
  212 
  213         printf("MEMGUARD DEBUGGING ALLOCATOR INITIALIZED:\n");
  214         printf("\tMEMGUARD map base: 0x%lx\n", (u_long)base);
  215         printf("\tMEMGUARD map size: %jd KBytes\n",
  216             (uintmax_t)memguard_mapsize >> 10);
  217 }
  218 
  219 /*
  220  * Run things that can't be done as early as memguard_init().
  221  */
  222 static void
  223 memguard_sysinit(void)
  224 {
  225         struct sysctl_oid_list *parent;
  226 
  227         parent = SYSCTL_STATIC_CHILDREN(_vm_memguard);
  228 
  229         SYSCTL_ADD_UAUTO(NULL, parent, OID_AUTO, "mapstart", CTLFLAG_RD,
  230             &memguard_base, "MemGuard KVA base");
  231         SYSCTL_ADD_UAUTO(NULL, parent, OID_AUTO, "maplimit", CTLFLAG_RD,
  232             &memguard_mapsize, "MemGuard KVA size");
  233 #if 0
  234         SYSCTL_ADD_ULONG(NULL, parent, OID_AUTO, "mapused", CTLFLAG_RD,
  235             &memguard_map->size, "MemGuard KVA used");
  236 #endif
  237 }
  238 SYSINIT(memguard, SI_SUB_KLD, SI_ORDER_ANY, memguard_sysinit, NULL);
  239 
  240 /*
  241  * v2sizep() converts a virtual address of the first page allocated for
  242  * an item to a pointer to u_long recording the size of the original
  243  * allocation request.
  244  *
  245  * This routine is very similar to those defined by UMA in uma_int.h.
  246  * The difference is that this routine stores the originally allocated
  247  * size in one of the page's fields that is unused when the page is
  248  * wired rather than the object field, which is used.
  249  */
  250 static u_long *
  251 v2sizep(vm_offset_t va)
  252 {
  253         vm_paddr_t pa;
  254         struct vm_page *p;
  255 
  256         pa = pmap_kextract(va);
  257         if (pa == 0)
  258                 panic("MemGuard detected double-free of %p", (void *)va);
  259         p = PHYS_TO_VM_PAGE(pa);
  260         KASSERT(p->wire_count != 0 && p->queue == PQ_NONE,
  261             ("MEMGUARD: Expected wired page %p in vtomgfifo!", p));
  262         return (&p->plinks.memguard.p);
  263 }
  264 
  265 static u_long *
  266 v2sizev(vm_offset_t va)
  267 {
  268         vm_paddr_t pa;
  269         struct vm_page *p;
  270 
  271         pa = pmap_kextract(va);
  272         if (pa == 0)
  273                 panic("MemGuard detected double-free of %p", (void *)va);
  274         p = PHYS_TO_VM_PAGE(pa);
  275         KASSERT(p->wire_count != 0 && p->queue == PQ_NONE,
  276             ("MEMGUARD: Expected wired page %p in vtomgfifo!", p));
  277         return (&p->plinks.memguard.v);
  278 }
  279 
  280 /*
  281  * Allocate a single object of specified size with specified flags
  282  * (either M_WAITOK or M_NOWAIT).
  283  */
  284 void *
  285 memguard_alloc(unsigned long req_size, int flags)
  286 {
  287         vm_offset_t addr, origaddr;
  288         u_long size_p, size_v;
  289         int do_guard, rv;
  290 
  291         size_p = round_page(req_size);
  292         if (size_p == 0)
  293                 return (NULL);
  294         /*
  295          * To ensure there are holes on both sides of the allocation,
  296          * request 2 extra pages of KVA.  We will only actually add a
  297          * vm_map_entry and get pages for the original request.  Save
  298          * the value of memguard_options so we have a consistent
  299          * value.
  300          */
  301         size_v = size_p;
  302         do_guard = (memguard_options & MG_GUARD_AROUND) != 0;
  303         if (do_guard)
  304                 size_v += 2 * PAGE_SIZE;
  305 
  306         /*
  307          * When we pass our memory limit, reject sub-page allocations.
  308          * Page-size and larger allocations will use the same amount
  309          * of physical memory whether we allocate or hand off to
  310          * uma_large_alloc(), so keep those.
  311          */
  312         if (vmem_size(memguard_arena, VMEM_ALLOC) >= memguard_physlimit &&
  313             req_size < PAGE_SIZE) {
  314                 addr = (vm_offset_t)NULL;
  315                 memguard_fail_pgs++;
  316                 goto out;
  317         }
  318         /*
  319          * Keep a moving cursor so we don't recycle KVA as long as
  320          * possible.  It's not perfect, since we don't know in what
  321          * order previous allocations will be free'd, but it's simple
  322          * and fast, and requires O(1) additional storage if guard
  323          * pages are not used.
  324          *
  325          * XXX This scheme will lead to greater fragmentation of the
  326          * map, unless vm_map_findspace() is tweaked.
  327          */
  328         for (;;) {
  329                 if (vmem_xalloc(memguard_arena, size_v, 0, 0, 0,
  330                     memguard_cursor, VMEM_ADDR_MAX,
  331                     M_BESTFIT | M_NOWAIT, &origaddr) == 0)
  332                         break;
  333                 /*
  334                  * The map has no space.  This may be due to
  335                  * fragmentation, or because the cursor is near the
  336                  * end of the map.
  337                  */
  338                 if (memguard_cursor == memguard_base) {
  339                         memguard_fail_kva++;
  340                         addr = (vm_offset_t)NULL;
  341                         goto out;
  342                 }
  343                 memguard_wrap++;
  344                 memguard_cursor = memguard_base;
  345         }
  346         addr = origaddr;
  347         if (do_guard)
  348                 addr += PAGE_SIZE;
  349         rv = kmem_back(kmem_object, addr, size_p, flags);
  350         if (rv != KERN_SUCCESS) {
  351                 vmem_xfree(memguard_arena, origaddr, size_v);
  352                 memguard_fail_pgs++;
  353                 addr = (vm_offset_t)NULL;
  354                 goto out;
  355         }
  356         memguard_cursor = addr + size_v;
  357         *v2sizep(trunc_page(addr)) = req_size;
  358         *v2sizev(trunc_page(addr)) = size_v;
  359         memguard_succ++;
  360         if (req_size < PAGE_SIZE) {
  361                 memguard_wasted += (PAGE_SIZE - req_size);
  362                 if (do_guard) {
  363                         /*
  364                          * Align the request to 16 bytes, and return
  365                          * an address near the end of the page, to
  366                          * better detect array overrun.
  367                          */
  368                         req_size = roundup2(req_size, 16);
  369                         addr += (PAGE_SIZE - req_size);
  370                 }
  371         }
  372 out:
  373         return ((void *)addr);
  374 }
  375 
  376 int
  377 is_memguard_addr(void *addr)
  378 {
  379         vm_offset_t a = (vm_offset_t)(uintptr_t)addr;
  380 
  381         return (a >= memguard_base && a < memguard_base + memguard_mapsize);
  382 }
  383 
  384 /*
  385  * Free specified single object.
  386  */
  387 void
  388 memguard_free(void *ptr)
  389 {
  390         vm_offset_t addr;
  391         u_long req_size, size, sizev;
  392         char *temp;
  393         int i;
  394 
  395         addr = trunc_page((uintptr_t)ptr);
  396         req_size = *v2sizep(addr);
  397         sizev = *v2sizev(addr);
  398         size = round_page(req_size);
  399 
  400         /*
  401          * Page should not be guarded right now, so force a write.
  402          * The purpose of this is to increase the likelihood of
  403          * catching a double-free, but not necessarily a
  404          * tamper-after-free (the second thread freeing might not
  405          * write before freeing, so this forces it to and,
  406          * subsequently, trigger a fault).
  407          */
  408         temp = ptr;
  409         for (i = 0; i < size; i += PAGE_SIZE)
  410                 temp[i] = 'M';
  411 
  412         /*
  413          * This requires carnal knowledge of the implementation of
  414          * kmem_free(), but since we've already replaced kmem_malloc()
  415          * above, it's not really any worse.  We want to use the
  416          * vm_map lock to serialize updates to memguard_wasted, since
  417          * we had the lock at increment.
  418          */
  419         kmem_unback(kmem_object, addr, size);
  420         if (sizev > size)
  421                 addr -= PAGE_SIZE;
  422         vmem_xfree(memguard_arena, addr, sizev);
  423         if (req_size < PAGE_SIZE)
  424                 memguard_wasted -= (PAGE_SIZE - req_size);
  425 }
  426 
  427 /*
  428  * Re-allocate an allocation that was originally guarded.
  429  */
  430 void *
  431 memguard_realloc(void *addr, unsigned long size, struct malloc_type *mtp,
  432     int flags)
  433 {
  434         void *newaddr;
  435         u_long old_size;
  436 
  437         /*
  438          * Allocate the new block.  Force the allocation to be guarded
  439          * as the original may have been guarded through random
  440          * chance, and that should be preserved.
  441          */
  442         if ((newaddr = memguard_alloc(size, flags)) == NULL)
  443                 return (NULL);
  444 
  445         /* Copy over original contents. */
  446         old_size = *v2sizep(trunc_page((uintptr_t)addr));
  447         bcopy(addr, newaddr, min(size, old_size));
  448         memguard_free(addr);
  449         return (newaddr);
  450 }
  451 
  452 static int
  453 memguard_cmp(unsigned long size)
  454 {
  455 
  456         if (size < memguard_minsize) {
  457                 memguard_minsize_reject++;
  458                 return (0);
  459         }
  460         if ((memguard_options & MG_GUARD_ALLLARGE) != 0 && size >= PAGE_SIZE)
  461                 return (1);
  462         if (memguard_frequency > 0 &&
  463             (random() % 100000) < memguard_frequency) {
  464                 memguard_frequency_hits++;
  465                 return (1);
  466         }
  467 
  468         return (0);
  469 }
  470 
  471 int
  472 memguard_cmp_mtp(struct malloc_type *mtp, unsigned long size)
  473 {
  474 
  475         if (memguard_cmp(size))
  476                 return(1);
  477 
  478 #if 1
  479         /*
  480          * The safest way of comparsion is to always compare short description
  481          * string of memory type, but it is also the slowest way.
  482          */
  483         return (strcmp(mtp->ks_shortdesc, vm_memguard_desc) == 0);
  484 #else
  485         /*
  486          * If we compare pointers, there are two possible problems:
  487          * 1. Memory type was unloaded and new memory type was allocated at the
  488          *    same address.
  489          * 2. Memory type was unloaded and loaded again, but allocated at a
  490          *    different address.
  491          */
  492         if (vm_memguard_mtype != NULL)
  493                 return (mtp == vm_memguard_mtype);
  494         if (strcmp(mtp->ks_shortdesc, vm_memguard_desc) == 0) {
  495                 vm_memguard_mtype = mtp;
  496                 return (1);
  497         }
  498         return (0);
  499 #endif
  500 }
  501 
  502 int
  503 memguard_cmp_zone(uma_zone_t zone)
  504 {
  505 
  506         if ((memguard_options & MG_GUARD_NOFREE) == 0 &&
  507             zone->uz_flags & UMA_ZONE_NOFREE)
  508                 return (0);
  509 
  510         if (memguard_cmp(zone->uz_size))
  511                 return (1);
  512 
  513         /*
  514          * The safest way of comparsion is to always compare zone name,
  515          * but it is also the slowest way.
  516          */
  517         return (strcmp(zone->uz_name, vm_memguard_desc) == 0);
  518 }

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