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

     /*
      * Copyright (c) 2005,
      *     Bosko Milekic <bmilekic@FreeBSD.org>.  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 <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 <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/vm_page.h>
    #include <vm/vm_map.h>
    #include <vm/vm_extern.h>
    #include <vm/memguard.h>
    
    /*
     * The maximum number of pages allowed per allocation.  If you're using
     * MemGuard to override very large items (> MAX_PAGES_PER_ITEM in size),
     * you need to increase MAX_PAGES_PER_ITEM.
     */
    #define MAX_PAGES_PER_ITEM      64
    
    SYSCTL_NODE(_vm, OID_AUTO, memguard, CTLFLAG_RW, NULL, "MemGuard data");
    /*
     * The vm_memguard_divisor variable controls how much of kmem_map should be
     * reserved for MemGuard.
     */
    u_int vm_memguard_divisor;
    SYSCTL_UINT(_vm_memguard, OID_AUTO, divisor, CTLFLAG_RD, &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)
    {
            struct malloc_type_internal *mtip;
            struct malloc_type_stats *mtsp;
            struct malloc_type *mtp;
            char desc[128];
            long bytes;
            int error, i;
    
            strlcpy(desc, vm_memguard_desc, sizeof(desc));
            error = sysctl_handle_string(oidp, desc, sizeof(desc), req);
            if (error != 0 || req->newptr == NULL)
                    return (error);
    
            /*
             * We can change memory type when no memory has been allocated for it
             * or when there is no such memory type yet (ie. it will be loaded with
             * kernel module).
             */
            bytes = 0;
            mtx_lock(&malloc_mtx);
           mtp = malloc_desc2type(desc);
           if (mtp != NULL) {
                   mtip = mtp->ks_handle;
                   for (i = 0; i < MAXCPU; i++) {
                           mtsp = &mtip->mti_stats[i];
                           bytes += mtsp->mts_memalloced;
                           bytes -= mtsp->mts_memfreed;
                   }
           }
           if (bytes > 0)
                   error = EBUSY;
           else {
                   /*
                    * If mtp is NULL, it will be initialized in memguard_cmp().
                    */
                   vm_memguard_mtype = mtp;
                   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, 0, 0,
       memguard_sysctl_desc, "A", "Short description of memory type to monitor");
   
   /*
    * Global MemGuard data.
    */
   static vm_map_t memguard_map;
   static unsigned long memguard_mapsize;
   static unsigned long memguard_mapused;
   struct memguard_entry {
           STAILQ_ENTRY(memguard_entry) entries;
           void *ptr;
   };
   static struct memguard_fifo {
           struct memguard_entry *stqh_first;
           struct memguard_entry **stqh_last;
           int index;
   } memguard_fifo_pool[MAX_PAGES_PER_ITEM];
   
   /*
    * Local prototypes.
    */
   static void memguard_guard(void *addr, int numpgs);
   static void memguard_unguard(void *addr, int numpgs);
   static struct memguard_fifo *vtomgfifo(vm_offset_t va);
   static void vsetmgfifo(vm_offset_t va, struct memguard_fifo *mgfifo);
   static void vclrmgfifo(vm_offset_t va);
   
   /*
    * Local macros.  MemGuard data is global, so replace these with whatever
    * your system uses to protect global data (if it is kernel-level
    * parallelized).  This is for porting among BSDs.
    */
   #define MEMGUARD_CRIT_SECTION_DECLARE   static struct mtx memguard_mtx
   #define MEMGUARD_CRIT_SECTION_INIT                              \
           mtx_init(&memguard_mtx, "MemGuard mtx", NULL, MTX_DEF)
   #define MEMGUARD_CRIT_SECTION_ENTER     mtx_lock(&memguard_mtx)
   #define MEMGUARD_CRIT_SECTION_EXIT      mtx_unlock(&memguard_mtx)
   MEMGUARD_CRIT_SECTION_DECLARE;
   
   /*
    * Initialize the MemGuard mock allocator.  All objects from MemGuard come
    * out of a single VM map (contiguous chunk of address space).
    */
   void
   memguard_init(vm_map_t parent_map, unsigned long size)
   {
           char *base, *limit;
           int i;
   
           /* size must be multiple of PAGE_SIZE */
           size /= PAGE_SIZE;
           size++;
           size *= PAGE_SIZE;
   
           memguard_map = kmem_suballoc(parent_map, (vm_offset_t *)&base,
               (vm_offset_t *)&limit, (vm_size_t)size);
           memguard_map->system_map = 1;
           memguard_mapsize = size;
           memguard_mapused = 0;
   
           MEMGUARD_CRIT_SECTION_INIT;
           MEMGUARD_CRIT_SECTION_ENTER;
           for (i = 0; i < MAX_PAGES_PER_ITEM; i++) {
                   STAILQ_INIT(&memguard_fifo_pool[i]);
                   memguard_fifo_pool[i].index = i;
           }
           MEMGUARD_CRIT_SECTION_EXIT;
   
           printf("MEMGUARD DEBUGGING ALLOCATOR INITIALIZED:\n");
           printf("\tMEMGUARD map base: %p\n", base);
           printf("\tMEMGUARD map limit: %p\n", limit);
           printf("\tMEMGUARD map size: %ld (Bytes)\n", size);
   }
   
   /*
    * Allocate a single object of specified size with specified flags (either
    * M_WAITOK or M_NOWAIT).
    */
   void *
   memguard_alloc(unsigned long size, int flags)
   {
           void *obj;
           struct memguard_entry *e = NULL;
           int numpgs;
   
           numpgs = size / PAGE_SIZE;
           if ((size % PAGE_SIZE) != 0)
                   numpgs++;
           if (numpgs > MAX_PAGES_PER_ITEM)
                   panic("MEMGUARD: You must increase MAX_PAGES_PER_ITEM " \
                       "in memguard.c (requested: %d pages)", numpgs);
           if (numpgs == 0)
                   return NULL;
   
           /*
            * If we haven't exhausted the memguard_map yet, allocate from
            * it and grab a new page, even if we have recycled pages in our
            * FIFO.  This is because we wish to allow recycled pages to live
            * guarded in the FIFO for as long as possible in order to catch
            * even very late tamper-after-frees, even though it means that
            * we end up wasting more memory, this is only a DEBUGGING allocator
            * after all.
            */
           MEMGUARD_CRIT_SECTION_ENTER;
           if (memguard_mapused >= memguard_mapsize) {
                   e = STAILQ_FIRST(&memguard_fifo_pool[numpgs - 1]);
                   if (e != NULL) {
                           STAILQ_REMOVE(&memguard_fifo_pool[numpgs - 1], e,
                               memguard_entry, entries);
                           MEMGUARD_CRIT_SECTION_EXIT;
                           obj = e->ptr;
                           free(e, M_TEMP);
                           memguard_unguard(obj, numpgs);
                           if (flags & M_ZERO)
                                   bzero(obj, PAGE_SIZE * numpgs);
                           return obj;
                   }
                   MEMGUARD_CRIT_SECTION_EXIT;
                   if (flags & M_WAITOK)
                           panic("MEMGUARD: Failed with M_WAITOK: " \
                               "memguard_map too small");
                   return NULL;
           }
           memguard_mapused += (PAGE_SIZE * numpgs);
           MEMGUARD_CRIT_SECTION_EXIT;
   
           obj = (void *)kmem_malloc(memguard_map, PAGE_SIZE * numpgs, flags);
           if (obj != NULL) {
                   vsetmgfifo((vm_offset_t)obj, &memguard_fifo_pool[numpgs - 1]);
                   if (flags & M_ZERO)
                           bzero(obj, PAGE_SIZE * numpgs);
           } else {
                   MEMGUARD_CRIT_SECTION_ENTER;
                   memguard_mapused -= (PAGE_SIZE * numpgs);
                   MEMGUARD_CRIT_SECTION_EXIT;
           }
           return obj;
   }
   
   /*
    * Free specified single object.
    */
   void
   memguard_free(void *addr)
   {
           struct memguard_entry *e;
           struct memguard_fifo *mgfifo;
           int idx;
           int *temp;
   
           addr = (void *)trunc_page((unsigned long)addr);
   
           /*
            * Page should not be guarded by 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 = (int *)((unsigned long)addr + (PAGE_SIZE/2));    /* in page */
           *temp = 0xd34dc0d3;
   
           mgfifo = vtomgfifo((vm_offset_t)addr);
           idx = mgfifo->index;
           memguard_guard(addr, idx + 1);
           e = malloc(sizeof(struct memguard_entry), M_TEMP, M_NOWAIT);
           if (e == NULL) {
                   MEMGUARD_CRIT_SECTION_ENTER;
                   memguard_mapused -= (PAGE_SIZE * (idx + 1));
                   MEMGUARD_CRIT_SECTION_EXIT;
                   memguard_unguard(addr, idx + 1);        /* just in case */
                   vclrmgfifo((vm_offset_t)addr);
                   kmem_free(memguard_map, (vm_offset_t)addr,
                       PAGE_SIZE * (idx + 1));
                   return;
           }
           e->ptr = addr;
           MEMGUARD_CRIT_SECTION_ENTER;
           STAILQ_INSERT_TAIL(mgfifo, e, entries);
           MEMGUARD_CRIT_SECTION_EXIT;
   }
   
   int
   memguard_cmp(struct malloc_type *mtp)
   {
   
   #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
   }
   
   /*
    * Guard a page containing specified object (make it read-only so that
    * future writes to it fail).
    */
   static void
   memguard_guard(void *addr, int numpgs)
   {
           void *a = (void *)trunc_page((unsigned long)addr);
           if (vm_map_protect(memguard_map, (vm_offset_t)a,
               (vm_offset_t)((unsigned long)a + (PAGE_SIZE * numpgs)),
               VM_PROT_READ, FALSE) != KERN_SUCCESS)
                   panic("MEMGUARD: Unable to guard page!");
   }
   
   /*
    * Unguard a page containing specified object (make it read-and-write to
    * allow full data access).
    */
   static void
   memguard_unguard(void *addr, int numpgs)
   {
           void *a = (void *)trunc_page((unsigned long)addr);
           if (vm_map_protect(memguard_map, (vm_offset_t)a,
               (vm_offset_t)((unsigned long)a + (PAGE_SIZE * numpgs)),
               VM_PROT_DEFAULT, FALSE) != KERN_SUCCESS)
                   panic("MEMGUARD: Unable to unguard page!");
   }
   
   /*
    * vtomgfifo() converts a virtual address of the first page allocated for
    * an item to a memguard_fifo_pool reference for the corresponding item's
    * size.
    *
    * vsetmgfifo() sets a reference in an underlying page for the specified
    * virtual address to an appropriate memguard_fifo_pool.
    *
    * These routines are very similar to those defined by UMA in uma_int.h.
    * The difference is that these routines store the mgfifo in one of the
    * page's fields that is unused when the page is wired rather than the
    * object field, which is used.
    */
   static struct memguard_fifo *
   vtomgfifo(vm_offset_t va)
   {
           vm_page_t p;
           struct memguard_fifo *mgfifo;
   
           p = PHYS_TO_VM_PAGE(pmap_kextract(va));
           KASSERT(p->wire_count != 0 && p->queue == PQ_NONE,
               ("MEMGUARD: Expected wired page in vtomgfifo!"));
           mgfifo = (struct memguard_fifo *)p->pageq.tqe_next;
           return mgfifo;
   }
   
   static void
   vsetmgfifo(vm_offset_t va, struct memguard_fifo *mgfifo)
   {
           vm_page_t p;
   
           p = PHYS_TO_VM_PAGE(pmap_kextract(va));
           KASSERT(p->wire_count != 0 && p->queue == PQ_NONE,
               ("MEMGUARD: Expected wired page in vsetmgfifo!"));
           p->pageq.tqe_next = (vm_page_t)mgfifo;
   }
   
   static void vclrmgfifo(vm_offset_t va)
   {
           vm_page_t p;
   
           p = PHYS_TO_VM_PAGE(pmap_kextract(va));
           KASSERT(p->wire_count != 0 && p->queue == PQ_NONE,
               ("MEMGUARD: Expected wired page in vclrmgfifo!"));
           p->pageq.tqe_next = NULL;
   }

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