FreeBSD/Linux Kernel Cross Reference
sys/vm/memguard.c

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2005, Bosko Milekic <bmilekic@FreeBSD.org>.
      * Copyright (c) 2010 Isilon Systems, Inc. (http://www.isilon.com/)
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice unmodified, this list of conditions, and the following
     *    disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    /*
     * MemGuard is a simple replacement allocator for debugging only
     * which provides ElectricFence-style memory barrier protection on
     * objects being allocated, and is used to detect tampering-after-free
     * scenarios.
     *
     * See the memguard(9) man page for more information on using MemGuard.
     */
    
    #include "opt_vm.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/types.h>
    #include <sys/queue.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/malloc.h>
    #include <sys/sysctl.h>
    #include <sys/vmem.h>
    #include <sys/vmmeter.h>
    
    #include <vm/vm.h>
    #include <vm/uma.h>
    #include <vm/vm_param.h>
    #include <vm/vm_page.h>
    #include <vm/vm_map.h>
    #include <vm/vm_object.h>
    #include <vm/vm_kern.h>
    #include <vm/vm_extern.h>
    #include <vm/uma_int.h>
    #include <vm/memguard.h>
    
    static SYSCTL_NODE(_vm, OID_AUTO, memguard, CTLFLAG_RW | CTLFLAG_MPSAFE, NULL,
        "MemGuard data");
    /*
     * The vm_memguard_divisor variable controls how much of kernel_arena should be
     * reserved for MemGuard.
     */
    static u_int vm_memguard_divisor;
    SYSCTL_UINT(_vm_memguard, OID_AUTO, divisor, CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
        &vm_memguard_divisor,
        0, "(kmem_size/memguard_divisor) == memguard submap size");
    
    /*
     * Short description (ks_shortdesc) of memory type to monitor.
     */
    static char vm_memguard_desc[128] = "";
    static struct malloc_type *vm_memguard_mtype = NULL;
    TUNABLE_STR("vm.memguard.desc", vm_memguard_desc, sizeof(vm_memguard_desc));
    static int
    memguard_sysctl_desc(SYSCTL_HANDLER_ARGS)
    {
            char desc[sizeof(vm_memguard_desc)];
            int error;
    
            strlcpy(desc, vm_memguard_desc, sizeof(desc));
            error = sysctl_handle_string(oidp, desc, sizeof(desc), req);
            if (error != 0 || req->newptr == NULL)
                    return (error);
    
            mtx_lock(&malloc_mtx);
            /* If mtp is NULL, it will be initialized in memguard_cmp() */
            vm_memguard_mtype = malloc_desc2type(desc);
            strlcpy(vm_memguard_desc, desc, sizeof(vm_memguard_desc));
            mtx_unlock(&malloc_mtx);
           return (error);
   }
   SYSCTL_PROC(_vm_memguard, OID_AUTO, desc,
       CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 0,
       memguard_sysctl_desc, "A", "Short description of memory type to monitor");
   
   static int
   memguard_sysctl_mapused(SYSCTL_HANDLER_ARGS)
   {
           vmem_size_t size;
   
           size = vmem_size(memguard_arena, VMEM_ALLOC);
           return (sysctl_handle_long(oidp, &size, sizeof(size), req));
   }
   
   static vm_offset_t memguard_base;
   static vm_size_t memguard_mapsize;
   static vm_size_t memguard_physlimit;
   static u_long memguard_wasted;
   static u_long memguard_succ;
   static u_long memguard_fail_kva;
   static u_long memguard_fail_pgs;
   
   SYSCTL_ULONG(_vm_memguard, OID_AUTO, mapsize, CTLFLAG_RD,
       &memguard_mapsize, 0, "MemGuard private arena size");
   SYSCTL_ULONG(_vm_memguard, OID_AUTO, phys_limit, CTLFLAG_RD,
       &memguard_physlimit, 0, "Limit on MemGuard memory consumption");
   SYSCTL_ULONG(_vm_memguard, OID_AUTO, wasted, CTLFLAG_RD,
       &memguard_wasted, 0, "Excess memory used through page promotion");
   SYSCTL_ULONG(_vm_memguard, OID_AUTO, numalloc, CTLFLAG_RD,
       &memguard_succ, 0, "Count of successful MemGuard allocations");
   SYSCTL_ULONG(_vm_memguard, OID_AUTO, fail_kva, CTLFLAG_RD,
       &memguard_fail_kva, 0, "MemGuard failures due to lack of KVA");
   SYSCTL_ULONG(_vm_memguard, OID_AUTO, fail_pgs, CTLFLAG_RD,
       &memguard_fail_pgs, 0, "MemGuard failures due to lack of pages");
   
   #define MG_GUARD_AROUND         0x001
   #define MG_GUARD_ALLLARGE       0x002
   #define MG_GUARD_NOFREE         0x004
   static int memguard_options = MG_GUARD_AROUND;
   SYSCTL_INT(_vm_memguard, OID_AUTO, options, CTLFLAG_RWTUN,
       &memguard_options, 0,
       "MemGuard options:\n"
       "\t0x001 - add guard pages around each allocation\n"
       "\t0x002 - always use MemGuard for allocations over a page\n"
       "\t0x004 - guard uma(9) zones with UMA_ZONE_NOFREE flag");
   
   static u_int memguard_minsize;
   static u_long memguard_minsize_reject;
   SYSCTL_UINT(_vm_memguard, OID_AUTO, minsize, CTLFLAG_RW,
       &memguard_minsize, 0, "Minimum size for page promotion");
   SYSCTL_ULONG(_vm_memguard, OID_AUTO, minsize_reject, CTLFLAG_RD,
       &memguard_minsize_reject, 0, "# times rejected for size");
   
   static u_int memguard_frequency;
   static u_long memguard_frequency_hits;
   SYSCTL_UINT(_vm_memguard, OID_AUTO, frequency, CTLFLAG_RWTUN,
       &memguard_frequency, 0, "Times in 100000 that MemGuard will randomly run");
   SYSCTL_ULONG(_vm_memguard, OID_AUTO, frequency_hits, CTLFLAG_RD,
       &memguard_frequency_hits, 0, "# times MemGuard randomly chose");
   
   /*
    * Return a fudged value to be used for vm_kmem_size for allocating
    * the kernel_arena.
    */
   unsigned long
   memguard_fudge(unsigned long km_size, const struct vm_map *parent_map)
   {
           u_long mem_pgs, parent_size;
   
           vm_memguard_divisor = 10;
           /* CTFLAG_RDTUN doesn't work during the early boot process. */
           TUNABLE_INT_FETCH("vm.memguard.divisor", &vm_memguard_divisor);
   
           parent_size = vm_map_max(parent_map) - vm_map_min(parent_map) +
               PAGE_SIZE;
           /* Pick a conservative value if provided value sucks. */
           if ((vm_memguard_divisor <= 0) ||
               ((parent_size / vm_memguard_divisor) == 0))
                   vm_memguard_divisor = 10;
           /*
            * Limit consumption of physical pages to
            * 1/vm_memguard_divisor of system memory.  If the KVA is
            * smaller than this then the KVA limit comes into play first.
            * This prevents memguard's page promotions from completely
            * using up memory, since most malloc(9) calls are sub-page.
            */
           mem_pgs = vm_cnt.v_page_count;
           memguard_physlimit = (mem_pgs / vm_memguard_divisor) * PAGE_SIZE;
           /*
            * We want as much KVA as we can take safely.  Use at most our
            * allotted fraction of the parent map's size.  Limit this to
            * twice the physical memory to avoid using too much memory as
            * pagetable pages (size must be multiple of PAGE_SIZE).
            */
           memguard_mapsize = round_page(parent_size / vm_memguard_divisor);
           if (memguard_mapsize / (2 * PAGE_SIZE) > mem_pgs)
                   memguard_mapsize = mem_pgs * 2 * PAGE_SIZE;
           if (km_size + memguard_mapsize > parent_size)
                   memguard_mapsize = 0;
           return (km_size + memguard_mapsize);
   }
   
   /*
    * Initialize the MemGuard mock allocator.  All objects from MemGuard come
    * out of a single contiguous chunk of kernel address space that is managed
    * by a vmem arena.
    */
   void
   memguard_init(vmem_t *parent)
   {
           vm_offset_t base;
   
           vmem_alloc(parent, memguard_mapsize, M_BESTFIT | M_WAITOK, &base);
           vmem_init(memguard_arena, "memguard arena", base, memguard_mapsize,
               PAGE_SIZE, 0, M_WAITOK);
           memguard_base = base;
   
           printf("MEMGUARD DEBUGGING ALLOCATOR INITIALIZED:\n");
           printf("\tMEMGUARD map base: 0x%lx\n", (u_long)base);
           printf("\tMEMGUARD map size: %jd KBytes\n",
               (uintmax_t)memguard_mapsize >> 10);
   }
   
   /*
    * Run things that can't be done as early as memguard_init().
    */
   static void
   memguard_sysinit(void)
   {
           struct sysctl_oid_list *parent;
   
           parent = SYSCTL_STATIC_CHILDREN(_vm_memguard);
           SYSCTL_ADD_UAUTO(NULL, parent, OID_AUTO, "mapstart",
               CTLFLAG_RD, &memguard_base,
               "MemGuard KVA base");
           SYSCTL_ADD_UAUTO(NULL, parent, OID_AUTO, "maplimit",
               CTLFLAG_RD, &memguard_mapsize,
               "MemGuard KVA size");
           SYSCTL_ADD_PROC(NULL, parent, OID_AUTO, "mapused",
               CTLFLAG_RD | CTLFLAG_MPSAFE | CTLTYPE_ULONG, NULL, 0, memguard_sysctl_mapused, "LU",
               "MemGuard KVA used");
   }
   SYSINIT(memguard, SI_SUB_KLD, SI_ORDER_ANY, memguard_sysinit, NULL);
   
   /*
    * v2sizep() converts a virtual address of the first page allocated for
    * an item to a pointer to u_long recording the size of the original
    * allocation request.
    *
    * This routine is very similar to those defined by UMA in uma_int.h.
    * The difference is that this routine stores the originally allocated
    * size in one of the page's fields that is unused when the page is
    * wired rather than the object field, which is used.
    */
   static u_long *
   v2sizep(vm_offset_t va)
   {
           vm_paddr_t pa;
           struct vm_page *p;
   
           pa = pmap_kextract(va);
           if (pa == 0)
                   panic("MemGuard detected double-free of %p", (void *)va);
           p = PHYS_TO_VM_PAGE(pa);
           KASSERT(vm_page_wired(p) && p->a.queue == PQ_NONE,
               ("MEMGUARD: Expected wired page %p in vtomgfifo!", p));
           return (&p->plinks.memguard.p);
   }
   
   static u_long *
   v2sizev(vm_offset_t va)
   {
           vm_paddr_t pa;
           struct vm_page *p;
   
           pa = pmap_kextract(va);
           if (pa == 0)
                   panic("MemGuard detected double-free of %p", (void *)va);
           p = PHYS_TO_VM_PAGE(pa);
           KASSERT(vm_page_wired(p) && p->a.queue == PQ_NONE,
               ("MEMGUARD: Expected wired page %p in vtomgfifo!", p));
           return (&p->plinks.memguard.v);
   }
   
   /*
    * Allocate a single object of specified size with specified flags
    * (either M_WAITOK or M_NOWAIT).
    */
   void *
   memguard_alloc(unsigned long req_size, int flags)
   {
           vm_offset_t addr, origaddr;
           u_long size_p, size_v;
           int do_guard, error, rv;
   
           size_p = round_page(req_size);
           if (size_p == 0)
                   return (NULL);
   
           /*
            * To ensure there are holes on both sides of the allocation,
            * request 2 extra pages of KVA.  Save the value of memguard_options
            * so that we use a consistent value throughout this function.
            */
           size_v = size_p;
           do_guard = (memguard_options & MG_GUARD_AROUND) != 0;
           if (do_guard)
                   size_v += 2 * PAGE_SIZE;
   
           /*
            * When we pass our memory limit, reject sub-page allocations.
            * Page-size and larger allocations will use the same amount
            * of physical memory whether we allocate or hand off to
            * malloc_large(), so keep those.
            */
           if (vmem_size(memguard_arena, VMEM_ALLOC) >= memguard_physlimit &&
               req_size < PAGE_SIZE) {
                   addr = (vm_offset_t)NULL;
                   memguard_fail_pgs++;
                   goto out;
           }
   
           /*
            * Attempt to avoid address reuse for as long as possible, to increase
            * the likelihood of catching a use-after-free.
            */
           error = vmem_alloc(memguard_arena, size_v, M_NEXTFIT | M_NOWAIT,
               &origaddr);
           if (error != 0) {
                   memguard_fail_kva++;
                   addr = (vm_offset_t)NULL;
                   goto out;
           }
           addr = origaddr;
           if (do_guard)
                   addr += PAGE_SIZE;
           rv = kmem_back(kernel_object, addr, size_p, flags);
           if (rv != KERN_SUCCESS) {
                   vmem_xfree(memguard_arena, origaddr, size_v);
                   memguard_fail_pgs++;
                   addr = (vm_offset_t)NULL;
                   goto out;
           }
           *v2sizep(trunc_page(addr)) = req_size;
           *v2sizev(trunc_page(addr)) = size_v;
           memguard_succ++;
           if (req_size < PAGE_SIZE) {
                   memguard_wasted += (PAGE_SIZE - req_size);
                   if (do_guard) {
                           /*
                            * Align the request to 16 bytes, and return
                            * an address near the end of the page, to
                            * better detect array overrun.
                            */
                           req_size = roundup2(req_size, 16);
                           addr += (PAGE_SIZE - req_size);
                   }
           }
   out:
           return ((void *)addr);
   }
   
   int
   is_memguard_addr(void *addr)
   {
           vm_offset_t a = (vm_offset_t)(uintptr_t)addr;
   
           return (a >= memguard_base && a < memguard_base + memguard_mapsize);
   }
   
   /*
    * Free specified single object.
    */
   void
   memguard_free(void *ptr)
   {
           vm_offset_t addr;
           u_long req_size, size, sizev;
           char *temp;
           int i;
   
           addr = trunc_page((uintptr_t)ptr);
           req_size = *v2sizep(addr);
           sizev = *v2sizev(addr);
           size = round_page(req_size);
   
           /*
            * Page should not be guarded right now, so force a write.
            * The purpose of this is to increase the likelihood of
            * catching a double-free, but not necessarily a
            * tamper-after-free (the second thread freeing might not
            * write before freeing, so this forces it to and,
            * subsequently, trigger a fault).
            */
           temp = ptr;
           for (i = 0; i < size; i += PAGE_SIZE)
                   temp[i] = 'M';
   
           /*
            * This requires carnal knowledge of the implementation of
            * kmem_free(), but since we've already replaced kmem_malloc()
            * above, it's not really any worse.  We want to use the
            * vm_map lock to serialize updates to memguard_wasted, since
            * we had the lock at increment.
            */
           kmem_unback(kernel_object, addr, size);
           if (sizev > size)
                   addr -= PAGE_SIZE;
           vmem_xfree(memguard_arena, addr, sizev);
           if (req_size < PAGE_SIZE)
                   memguard_wasted -= (PAGE_SIZE - req_size);
   }
   
   /*
    * Re-allocate an allocation that was originally guarded.
    */
   void *
   memguard_realloc(void *addr, unsigned long size, struct malloc_type *mtp,
       int flags)
   {
           void *newaddr;
           u_long old_size;
   
           /*
            * Allocate the new block.  Force the allocation to be guarded
            * as the original may have been guarded through random
            * chance, and that should be preserved.
            */
           if ((newaddr = memguard_alloc(size, flags)) == NULL)
                   return (NULL);
   
           /* Copy over original contents. */
           old_size = *v2sizep(trunc_page((uintptr_t)addr));
           bcopy(addr, newaddr, min(size, old_size));
           memguard_free(addr);
           return (newaddr);
   }
   
   static int
   memguard_cmp(unsigned long size)
   {
   
           if (size < memguard_minsize) {
                   memguard_minsize_reject++;
                   return (0);
           }
           if ((memguard_options & MG_GUARD_ALLLARGE) != 0 && size >= PAGE_SIZE)
                   return (1);
           if (memguard_frequency > 0 &&
               (random() % 100000) < memguard_frequency) {
                   memguard_frequency_hits++;
                   return (1);
           }
   
           return (0);
   }
   
   int
   memguard_cmp_mtp(struct malloc_type *mtp, unsigned long size)
   {
   
           if (memguard_cmp(size))
                   return(1);
   
   #if 1
           /*
            * The safest way of comparsion is to always compare short description
            * string of memory type, but it is also the slowest way.
            */
           return (strcmp(mtp->ks_shortdesc, vm_memguard_desc) == 0);
   #else
           /*
            * If we compare pointers, there are two possible problems:
            * 1. Memory type was unloaded and new memory type was allocated at the
            *    same address.
            * 2. Memory type was unloaded and loaded again, but allocated at a
            *    different address.
            */
           if (vm_memguard_mtype != NULL)
                   return (mtp == vm_memguard_mtype);
           if (strcmp(mtp->ks_shortdesc, vm_memguard_desc) == 0) {
                   vm_memguard_mtype = mtp;
                   return (1);
           }
           return (0);
   #endif
   }
   
   int
   memguard_cmp_zone(uma_zone_t zone)
   {
   
           if ((memguard_options & MG_GUARD_NOFREE) == 0 &&
               zone->uz_flags & UMA_ZONE_NOFREE)
                   return (0);
   
           if (memguard_cmp(zone->uz_size))
                   return (1);
   
           /*
            * The safest way of comparsion is to always compare zone name,
            * but it is also the slowest way.
            */
           return (strcmp(zone->uz_name, vm_memguard_desc) == 0);
   }
   
   unsigned long
   memguard_get_req_size(const void *addr)
   {
           return (*v2sizep(trunc_page((uintptr_t)addr)));
   }

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