The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: 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  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
    3  *
    4  * Copyright (c) 2005, Bosko Milekic <bmilekic@FreeBSD.org>.
    5  * Copyright (c) 2010 Isilon Systems, Inc. (http://www.isilon.com/)
    6  * All rights reserved.
    7  *
    8  * Redistribution and use in source and binary forms, with or without
    9  * modification, are permitted provided that the following conditions
   10  * are met:
   11  * 1. Redistributions of source code must retain the above copyright
   12  *    notice unmodified, this list of conditions, and the following
   13  *    disclaimer.
   14  * 2. Redistributions in binary form must reproduce the above copyright
   15  *    notice, this list of conditions and the following disclaimer in the
   16  *    documentation and/or other materials provided with the distribution.
   17  *
   18  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
   19  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   20  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   21  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
   22  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   23  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   24  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   25  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   26  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   27  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   28  */
   29 
   30 #include <sys/cdefs.h>
   31 __FBSDID("$FreeBSD: releng/12.0/sys/vm/memguard.c 326347 2017-11-28 23:40:54Z jeff $");
   32 
   33 /*
   34  * MemGuard is a simple replacement allocator for debugging only
   35  * which provides ElectricFence-style memory barrier protection on
   36  * objects being allocated, and is used to detect tampering-after-free
   37  * scenarios.
   38  *
   39  * See the memguard(9) man page for more information on using MemGuard.
   40  */
   41 
   42 #include "opt_vm.h"
   43 
   44 #include <sys/param.h>
   45 #include <sys/systm.h>
   46 #include <sys/kernel.h>
   47 #include <sys/types.h>
   48 #include <sys/queue.h>
   49 #include <sys/lock.h>
   50 #include <sys/mutex.h>
   51 #include <sys/malloc.h>
   52 #include <sys/sysctl.h>
   53 #include <sys/vmem.h>
   54 #include <sys/vmmeter.h>
   55 
   56 #include <vm/vm.h>
   57 #include <vm/uma.h>
   58 #include <vm/vm_param.h>
   59 #include <vm/vm_page.h>
   60 #include <vm/vm_map.h>
   61 #include <vm/vm_object.h>
   62 #include <vm/vm_kern.h>
   63 #include <vm/vm_extern.h>
   64 #include <vm/uma_int.h>
   65 #include <vm/memguard.h>
   66 
   67 static SYSCTL_NODE(_vm, OID_AUTO, memguard, CTLFLAG_RW, NULL, "MemGuard data");
   68 /*
   69  * The vm_memguard_divisor variable controls how much of kernel_arena should be
   70  * reserved for MemGuard.
   71  */
   72 static u_int vm_memguard_divisor;
   73 SYSCTL_UINT(_vm_memguard, OID_AUTO, divisor, CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
   74     &vm_memguard_divisor,
   75     0, "(kmem_size/memguard_divisor) == memguard submap size");
   76 
   77 /*
   78  * Short description (ks_shortdesc) of memory type to monitor.
   79  */
   80 static char vm_memguard_desc[128] = "";
   81 static struct malloc_type *vm_memguard_mtype = NULL;
   82 TUNABLE_STR("vm.memguard.desc", vm_memguard_desc, sizeof(vm_memguard_desc));
   83 static int
   84 memguard_sysctl_desc(SYSCTL_HANDLER_ARGS)
   85 {
   86         char desc[sizeof(vm_memguard_desc)];
   87         int error;
   88 
   89         strlcpy(desc, vm_memguard_desc, sizeof(desc));
   90         error = sysctl_handle_string(oidp, desc, sizeof(desc), req);
   91         if (error != 0 || req->newptr == NULL)
   92                 return (error);
   93 
   94         mtx_lock(&malloc_mtx);
   95         /* If mtp is NULL, it will be initialized in memguard_cmp() */
   96         vm_memguard_mtype = malloc_desc2type(desc);
   97         strlcpy(vm_memguard_desc, desc, sizeof(vm_memguard_desc));
   98         mtx_unlock(&malloc_mtx);
   99         return (error);
  100 }
  101 SYSCTL_PROC(_vm_memguard, OID_AUTO, desc,
  102     CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 0,
  103     memguard_sysctl_desc, "A", "Short description of memory type to monitor");
  104 
  105 static vm_offset_t memguard_cursor;
  106 static vm_offset_t memguard_base;
  107 static vm_size_t memguard_mapsize;
  108 static vm_size_t memguard_physlimit;
  109 static u_long memguard_wasted;
  110 static u_long memguard_wrap;
  111 static u_long memguard_succ;
  112 static u_long memguard_fail_kva;
  113 static u_long memguard_fail_pgs;
  114 
  115 SYSCTL_ULONG(_vm_memguard, OID_AUTO, cursor, CTLFLAG_RD,
  116     &memguard_cursor, 0, "MemGuard cursor");
  117 SYSCTL_ULONG(_vm_memguard, OID_AUTO, mapsize, CTLFLAG_RD,
  118     &memguard_mapsize, 0, "MemGuard private arena size");
  119 SYSCTL_ULONG(_vm_memguard, OID_AUTO, phys_limit, CTLFLAG_RD,
  120     &memguard_physlimit, 0, "Limit on MemGuard memory consumption");
  121 SYSCTL_ULONG(_vm_memguard, OID_AUTO, wasted, CTLFLAG_RD,
  122     &memguard_wasted, 0, "Excess memory used through page promotion");
  123 SYSCTL_ULONG(_vm_memguard, OID_AUTO, wrapcnt, CTLFLAG_RD,
  124     &memguard_wrap, 0, "MemGuard cursor wrap count");
  125 SYSCTL_ULONG(_vm_memguard, OID_AUTO, numalloc, CTLFLAG_RD,
  126     &memguard_succ, 0, "Count of successful MemGuard allocations");
  127 SYSCTL_ULONG(_vm_memguard, OID_AUTO, fail_kva, CTLFLAG_RD,
  128     &memguard_fail_kva, 0, "MemGuard failures due to lack of KVA");
  129 SYSCTL_ULONG(_vm_memguard, OID_AUTO, fail_pgs, CTLFLAG_RD,
  130     &memguard_fail_pgs, 0, "MemGuard failures due to lack of pages");
  131 
  132 #define MG_GUARD_AROUND         0x001
  133 #define MG_GUARD_ALLLARGE       0x002
  134 #define MG_GUARD_NOFREE         0x004
  135 static int memguard_options = MG_GUARD_AROUND;
  136 SYSCTL_INT(_vm_memguard, OID_AUTO, options, CTLFLAG_RWTUN,
  137     &memguard_options, 0,
  138     "MemGuard options:\n"
  139     "\t0x001 - add guard pages around each allocation\n"
  140     "\t0x002 - always use MemGuard for allocations over a page\n"
  141     "\t0x004 - guard uma(9) zones with UMA_ZONE_NOFREE flag");
  142 
  143 static u_int memguard_minsize;
  144 static u_long memguard_minsize_reject;
  145 SYSCTL_UINT(_vm_memguard, OID_AUTO, minsize, CTLFLAG_RW,
  146     &memguard_minsize, 0, "Minimum size for page promotion");
  147 SYSCTL_ULONG(_vm_memguard, OID_AUTO, minsize_reject, CTLFLAG_RD,
  148     &memguard_minsize_reject, 0, "# times rejected for size");
  149 
  150 static u_int memguard_frequency;
  151 static u_long memguard_frequency_hits;
  152 SYSCTL_UINT(_vm_memguard, OID_AUTO, frequency, CTLFLAG_RWTUN,
  153     &memguard_frequency, 0, "Times in 100000 that MemGuard will randomly run");
  154 SYSCTL_ULONG(_vm_memguard, OID_AUTO, frequency_hits, CTLFLAG_RD,
  155     &memguard_frequency_hits, 0, "# times MemGuard randomly chose");
  156 
  157 
  158 /*
  159  * Return a fudged value to be used for vm_kmem_size for allocating
  160  * the kernel_arena.  The memguard memory will be a submap.
  161  */
  162 unsigned long
  163 memguard_fudge(unsigned long km_size, const struct vm_map *parent_map)
  164 {
  165         u_long mem_pgs, parent_size;
  166 
  167         vm_memguard_divisor = 10;
  168         /* CTFLAG_RDTUN doesn't work during the early boot process. */
  169         TUNABLE_INT_FETCH("vm.memguard.divisor", &vm_memguard_divisor);
  170 
  171         parent_size = vm_map_max(parent_map) - vm_map_min(parent_map) +
  172             PAGE_SIZE;
  173         /* Pick a conservative value if provided value sucks. */
  174         if ((vm_memguard_divisor <= 0) ||
  175             ((parent_size / vm_memguard_divisor) == 0))
  176                 vm_memguard_divisor = 10;
  177         /*
  178          * Limit consumption of physical pages to
  179          * 1/vm_memguard_divisor of system memory.  If the KVA is
  180          * smaller than this then the KVA limit comes into play first.
  181          * This prevents memguard's page promotions from completely
  182          * using up memory, since most malloc(9) calls are sub-page.
  183          */
  184         mem_pgs = vm_cnt.v_page_count;
  185         memguard_physlimit = (mem_pgs / vm_memguard_divisor) * PAGE_SIZE;
  186         /*
  187          * We want as much KVA as we can take safely.  Use at most our
  188          * allotted fraction of the parent map's size.  Limit this to
  189          * twice the physical memory to avoid using too much memory as
  190          * pagetable pages (size must be multiple of PAGE_SIZE).
  191          */
  192         memguard_mapsize = round_page(parent_size / vm_memguard_divisor);
  193         if (memguard_mapsize / (2 * PAGE_SIZE) > mem_pgs)
  194                 memguard_mapsize = mem_pgs * 2 * PAGE_SIZE;
  195         if (km_size + memguard_mapsize > parent_size)
  196                 memguard_mapsize = 0;
  197         return (km_size + memguard_mapsize);
  198 }
  199 
  200 /*
  201  * Initialize the MemGuard mock allocator.  All objects from MemGuard come
  202  * out of a single VM map (contiguous chunk of address space).
  203  */
  204 void
  205 memguard_init(vmem_t *parent)
  206 {
  207         vm_offset_t base;
  208 
  209         vmem_alloc(parent, memguard_mapsize, M_BESTFIT | M_WAITOK, &base);
  210         vmem_init(memguard_arena, "memguard arena", base, memguard_mapsize,
  211             PAGE_SIZE, 0, M_WAITOK);
  212         memguard_cursor = base;
  213         memguard_base = base;
  214 
  215         printf("MEMGUARD DEBUGGING ALLOCATOR INITIALIZED:\n");
  216         printf("\tMEMGUARD map base: 0x%lx\n", (u_long)base);
  217         printf("\tMEMGUARD map size: %jd KBytes\n",
  218             (uintmax_t)memguard_mapsize >> 10);
  219 }
  220 
  221 /*
  222  * Run things that can't be done as early as memguard_init().
  223  */
  224 static void
  225 memguard_sysinit(void)
  226 {
  227         struct sysctl_oid_list *parent;
  228 
  229         parent = SYSCTL_STATIC_CHILDREN(_vm_memguard);
  230 
  231         SYSCTL_ADD_UAUTO(NULL, parent, OID_AUTO, "mapstart", CTLFLAG_RD,
  232             &memguard_base, "MemGuard KVA base");
  233         SYSCTL_ADD_UAUTO(NULL, parent, OID_AUTO, "maplimit", CTLFLAG_RD,
  234             &memguard_mapsize, "MemGuard KVA size");
  235 #if 0
  236         SYSCTL_ADD_ULONG(NULL, parent, OID_AUTO, "mapused", CTLFLAG_RD,
  237             &memguard_map->size, "MemGuard KVA used");
  238 #endif
  239 }
  240 SYSINIT(memguard, SI_SUB_KLD, SI_ORDER_ANY, memguard_sysinit, NULL);
  241 
  242 /*
  243  * v2sizep() converts a virtual address of the first page allocated for
  244  * an item to a pointer to u_long recording the size of the original
  245  * allocation request.
  246  *
  247  * This routine is very similar to those defined by UMA in uma_int.h.
  248  * The difference is that this routine stores the originally allocated
  249  * size in one of the page's fields that is unused when the page is
  250  * wired rather than the object field, which is used.
  251  */
  252 static u_long *
  253 v2sizep(vm_offset_t va)
  254 {
  255         vm_paddr_t pa;
  256         struct vm_page *p;
  257 
  258         pa = pmap_kextract(va);
  259         if (pa == 0)
  260                 panic("MemGuard detected double-free of %p", (void *)va);
  261         p = PHYS_TO_VM_PAGE(pa);
  262         KASSERT(p->wire_count != 0 && p->queue == PQ_NONE,
  263             ("MEMGUARD: Expected wired page %p in vtomgfifo!", p));
  264         return (&p->plinks.memguard.p);
  265 }
  266 
  267 static u_long *
  268 v2sizev(vm_offset_t va)
  269 {
  270         vm_paddr_t pa;
  271         struct vm_page *p;
  272 
  273         pa = pmap_kextract(va);
  274         if (pa == 0)
  275                 panic("MemGuard detected double-free of %p", (void *)va);
  276         p = PHYS_TO_VM_PAGE(pa);
  277         KASSERT(p->wire_count != 0 && p->queue == PQ_NONE,
  278             ("MEMGUARD: Expected wired page %p in vtomgfifo!", p));
  279         return (&p->plinks.memguard.v);
  280 }
  281 
  282 /*
  283  * Allocate a single object of specified size with specified flags
  284  * (either M_WAITOK or M_NOWAIT).
  285  */
  286 void *
  287 memguard_alloc(unsigned long req_size, int flags)
  288 {
  289         vm_offset_t addr, origaddr;
  290         u_long size_p, size_v;
  291         int do_guard, rv;
  292 
  293         size_p = round_page(req_size);
  294         if (size_p == 0)
  295                 return (NULL);
  296         /*
  297          * To ensure there are holes on both sides of the allocation,
  298          * request 2 extra pages of KVA.  We will only actually add a
  299          * vm_map_entry and get pages for the original request.  Save
  300          * the value of memguard_options so we have a consistent
  301          * value.
  302          */
  303         size_v = size_p;
  304         do_guard = (memguard_options & MG_GUARD_AROUND) != 0;
  305         if (do_guard)
  306                 size_v += 2 * PAGE_SIZE;
  307 
  308         /*
  309          * When we pass our memory limit, reject sub-page allocations.
  310          * Page-size and larger allocations will use the same amount
  311          * of physical memory whether we allocate or hand off to
  312          * uma_large_alloc(), so keep those.
  313          */
  314         if (vmem_size(memguard_arena, VMEM_ALLOC) >= memguard_physlimit &&
  315             req_size < PAGE_SIZE) {
  316                 addr = (vm_offset_t)NULL;
  317                 memguard_fail_pgs++;
  318                 goto out;
  319         }
  320         /*
  321          * Keep a moving cursor so we don't recycle KVA as long as
  322          * possible.  It's not perfect, since we don't know in what
  323          * order previous allocations will be free'd, but it's simple
  324          * and fast, and requires O(1) additional storage if guard
  325          * pages are not used.
  326          *
  327          * XXX This scheme will lead to greater fragmentation of the
  328          * map, unless vm_map_findspace() is tweaked.
  329          */
  330         for (;;) {
  331                 if (vmem_xalloc(memguard_arena, size_v, 0, 0, 0,
  332                     memguard_cursor, VMEM_ADDR_MAX,
  333                     M_BESTFIT | M_NOWAIT, &origaddr) == 0)
  334                         break;
  335                 /*
  336                  * The map has no space.  This may be due to
  337                  * fragmentation, or because the cursor is near the
  338                  * end of the map.
  339                  */
  340                 if (memguard_cursor == memguard_base) {
  341                         memguard_fail_kva++;
  342                         addr = (vm_offset_t)NULL;
  343                         goto out;
  344                 }
  345                 memguard_wrap++;
  346                 memguard_cursor = memguard_base;
  347         }
  348         addr = origaddr;
  349         if (do_guard)
  350                 addr += PAGE_SIZE;
  351         rv = kmem_back(kernel_object, addr, size_p, flags);
  352         if (rv != KERN_SUCCESS) {
  353                 vmem_xfree(memguard_arena, origaddr, size_v);
  354                 memguard_fail_pgs++;
  355                 addr = (vm_offset_t)NULL;
  356                 goto out;
  357         }
  358         memguard_cursor = addr + size_v;
  359         *v2sizep(trunc_page(addr)) = req_size;
  360         *v2sizev(trunc_page(addr)) = size_v;
  361         memguard_succ++;
  362         if (req_size < PAGE_SIZE) {
  363                 memguard_wasted += (PAGE_SIZE - req_size);
  364                 if (do_guard) {
  365                         /*
  366                          * Align the request to 16 bytes, and return
  367                          * an address near the end of the page, to
  368                          * better detect array overrun.
  369                          */
  370                         req_size = roundup2(req_size, 16);
  371                         addr += (PAGE_SIZE - req_size);
  372                 }
  373         }
  374 out:
  375         return ((void *)addr);
  376 }
  377 
  378 int
  379 is_memguard_addr(void *addr)
  380 {
  381         vm_offset_t a = (vm_offset_t)(uintptr_t)addr;
  382 
  383         return (a >= memguard_base && a < memguard_base + memguard_mapsize);
  384 }
  385 
  386 /*
  387  * Free specified single object.
  388  */
  389 void
  390 memguard_free(void *ptr)
  391 {
  392         vm_offset_t addr;
  393         u_long req_size, size, sizev;
  394         char *temp;
  395         int i;
  396 
  397         addr = trunc_page((uintptr_t)ptr);
  398         req_size = *v2sizep(addr);
  399         sizev = *v2sizev(addr);
  400         size = round_page(req_size);
  401 
  402         /*
  403          * Page should not be guarded right now, so force a write.
  404          * The purpose of this is to increase the likelihood of
  405          * catching a double-free, but not necessarily a
  406          * tamper-after-free (the second thread freeing might not
  407          * write before freeing, so this forces it to and,
  408          * subsequently, trigger a fault).
  409          */
  410         temp = ptr;
  411         for (i = 0; i < size; i += PAGE_SIZE)
  412                 temp[i] = 'M';
  413 
  414         /*
  415          * This requires carnal knowledge of the implementation of
  416          * kmem_free(), but since we've already replaced kmem_malloc()
  417          * above, it's not really any worse.  We want to use the
  418          * vm_map lock to serialize updates to memguard_wasted, since
  419          * we had the lock at increment.
  420          */
  421         kmem_unback(kernel_object, addr, size);
  422         if (sizev > size)
  423                 addr -= PAGE_SIZE;
  424         vmem_xfree(memguard_arena, addr, sizev);
  425         if (req_size < PAGE_SIZE)
  426                 memguard_wasted -= (PAGE_SIZE - req_size);
  427 }
  428 
  429 /*
  430  * Re-allocate an allocation that was originally guarded.
  431  */
  432 void *
  433 memguard_realloc(void *addr, unsigned long size, struct malloc_type *mtp,
  434     int flags)
  435 {
  436         void *newaddr;
  437         u_long old_size;
  438 
  439         /*
  440          * Allocate the new block.  Force the allocation to be guarded
  441          * as the original may have been guarded through random
  442          * chance, and that should be preserved.
  443          */
  444         if ((newaddr = memguard_alloc(size, flags)) == NULL)
  445                 return (NULL);
  446 
  447         /* Copy over original contents. */
  448         old_size = *v2sizep(trunc_page((uintptr_t)addr));
  449         bcopy(addr, newaddr, min(size, old_size));
  450         memguard_free(addr);
  451         return (newaddr);
  452 }
  453 
  454 static int
  455 memguard_cmp(unsigned long size)
  456 {
  457 
  458         if (size < memguard_minsize) {
  459                 memguard_minsize_reject++;
  460                 return (0);
  461         }
  462         if ((memguard_options & MG_GUARD_ALLLARGE) != 0 && size >= PAGE_SIZE)
  463                 return (1);
  464         if (memguard_frequency > 0 &&
  465             (random() % 100000) < memguard_frequency) {
  466                 memguard_frequency_hits++;
  467                 return (1);
  468         }
  469 
  470         return (0);
  471 }
  472 
  473 int
  474 memguard_cmp_mtp(struct malloc_type *mtp, unsigned long size)
  475 {
  476 
  477         if (memguard_cmp(size))
  478                 return(1);
  479 
  480 #if 1
  481         /*
  482          * The safest way of comparsion is to always compare short description
  483          * string of memory type, but it is also the slowest way.
  484          */
  485         return (strcmp(mtp->ks_shortdesc, vm_memguard_desc) == 0);
  486 #else
  487         /*
  488          * If we compare pointers, there are two possible problems:
  489          * 1. Memory type was unloaded and new memory type was allocated at the
  490          *    same address.
  491          * 2. Memory type was unloaded and loaded again, but allocated at a
  492          *    different address.
  493          */
  494         if (vm_memguard_mtype != NULL)
  495                 return (mtp == vm_memguard_mtype);
  496         if (strcmp(mtp->ks_shortdesc, vm_memguard_desc) == 0) {
  497                 vm_memguard_mtype = mtp;
  498                 return (1);
  499         }
  500         return (0);
  501 #endif
  502 }
  503 
  504 int
  505 memguard_cmp_zone(uma_zone_t zone)
  506 {
  507 
  508         if ((memguard_options & MG_GUARD_NOFREE) == 0 &&
  509             zone->uz_flags & UMA_ZONE_NOFREE)
  510                 return (0);
  511 
  512         if (memguard_cmp(zone->uz_size))
  513                 return (1);
  514 
  515         /*
  516          * The safest way of comparsion is to always compare zone name,
  517          * but it is also the slowest way.
  518          */
  519         return (strcmp(zone->uz_name, vm_memguard_desc) == 0);
  520 }

Cache object: e04503c50c57cc09a4f2763097426d31


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