Implement support for buffers larger than PAGE_SIZE in MemGuard. Adds
a little bit of complexity but performance requirements lacking (this is a debugging allocator after all), it's really not too bad (still only 317 lines). Also add an additional check to help catch really weird 3-threads-involved races: make memguard_free() write to the first page handed back, always, before it does anything else. Note that there is still a problem in VM+PMAP (specifically with vm_map_protect) w.r.t. MemGuard uses it, but this will be fixed shortly and this change stands on its own.
This commit is contained in:
Bosko Milekic
parent
ade68ea226
commit
0341256576
@ -46,11 +46,19 @@ __FBSDID("$FreeBSD$");
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#include <sys/malloc.h>
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#include <vm/vm.h>
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#include <vm/vm_param.h>
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#include <vm/vm_page.h>
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#include <vm/vm_map.h>
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#include <vm/vm_extern.h>
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#include <vm/memguard.h>
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/*
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* The maximum number of pages allowed per allocation. If you're using
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* MemGuard to override very large items (> MAX_PAGES_PER_ITEM in size),
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* you need to increase MAX_PAGES_PER_ITEM.
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*/
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#define MAX_PAGES_PER_ITEM 64
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/*
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* Global MemGuard data.
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*/
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@ -61,13 +69,20 @@ struct memguard_entry {
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STAILQ_ENTRY(memguard_entry) entries;
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void *ptr;
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};
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static STAILQ_HEAD(memguard_fifo, memguard_entry) memguard_fifo_pool;
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static struct memguard_fifo {
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struct memguard_entry *stqh_first;
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struct memguard_entry **stqh_last;
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int index;
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} memguard_fifo_pool[MAX_PAGES_PER_ITEM];
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/*
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* Local prototypes.
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*/
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static void memguard_guard(void *addr);
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static void memguard_unguard(void *addr);
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static void memguard_guard(void *addr, int numpgs);
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static void memguard_unguard(void *addr, int numpgs);
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static struct memguard_fifo *vtomgfifo(vm_offset_t va);
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static void vsetmgfifo(vm_offset_t va, struct memguard_fifo *mgfifo);
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static void vclrmgfifo(vm_offset_t va);
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/*
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* Local macros. MemGuard data is global, so replace these with whatever
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@ -89,6 +104,7 @@ void
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memguard_init(vm_map_t parent_map, unsigned long size)
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{
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char *base, *limit;
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int i;
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/* size must be multiple of PAGE_SIZE */
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size /= PAGE_SIZE;
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@ -103,7 +119,10 @@ memguard_init(vm_map_t parent_map, unsigned long size)
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MEMGUARD_CRIT_SECTION_INIT;
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MEMGUARD_CRIT_SECTION_ENTER;
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STAILQ_INIT(&memguard_fifo_pool);
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for (i = 0; i < MAX_PAGES_PER_ITEM; i++) {
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STAILQ_INIT(&memguard_fifo_pool[i]);
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memguard_fifo_pool[i].index = i;
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}
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MEMGUARD_CRIT_SECTION_EXIT;
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printf("MEMGUARD DEBUGGING ALLOCATOR INITIALIZED:\n");
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@ -119,12 +138,18 @@ memguard_init(vm_map_t parent_map, unsigned long size)
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void *
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memguard_alloc(unsigned long size, int flags)
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{
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void *obj = NULL;
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void *obj;
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struct memguard_entry *e = NULL;
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int numpgs;
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/* XXX: MemGuard does not handle > PAGE_SIZE objects. */
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if (size > PAGE_SIZE)
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panic("MEMGUARD: Cannot handle objects > PAGE_SIZE");
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numpgs = size / PAGE_SIZE;
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if ((size % PAGE_SIZE) != 0)
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numpgs++;
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if (numpgs > MAX_PAGES_PER_ITEM)
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panic("MEMGUARD: You must increase MAX_PAGES_PER_ITEM " \
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"in memguard.c (requested: %d pages)", numpgs);
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if (numpgs == 0)
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return NULL;
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/*
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* If we haven't exhausted the memguard_map yet, allocate from
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@ -137,16 +162,16 @@ memguard_alloc(unsigned long size, int flags)
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*/
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MEMGUARD_CRIT_SECTION_ENTER;
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if (memguard_mapused >= memguard_mapsize) {
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e = STAILQ_FIRST(&memguard_fifo_pool);
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e = STAILQ_FIRST(&memguard_fifo_pool[numpgs - 1]);
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if (e != NULL) {
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STAILQ_REMOVE(&memguard_fifo_pool, e,
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STAILQ_REMOVE(&memguard_fifo_pool[numpgs - 1], e,
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memguard_entry, entries);
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MEMGUARD_CRIT_SECTION_EXIT;
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obj = e->ptr;
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free(e, M_TEMP);
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memguard_unguard(obj);
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memguard_unguard(obj, numpgs);
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if (flags & M_ZERO)
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bzero(obj, PAGE_SIZE);
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bzero(obj, PAGE_SIZE * numpgs);
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return obj;
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}
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MEMGUARD_CRIT_SECTION_EXIT;
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@ -154,19 +179,18 @@ memguard_alloc(unsigned long size, int flags)
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panic("MEMGUARD: Failed with M_WAITOK: " \
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"memguard_map too small");
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return NULL;
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} else
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memguard_mapused += PAGE_SIZE;
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}
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memguard_mapused += (PAGE_SIZE * numpgs);
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MEMGUARD_CRIT_SECTION_EXIT;
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if (obj == NULL)
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obj = (void *)kmem_malloc(memguard_map, PAGE_SIZE, flags);
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obj = (void *)kmem_malloc(memguard_map, PAGE_SIZE * numpgs, flags);
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if (obj != NULL) {
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memguard_unguard(obj);
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vsetmgfifo((vm_offset_t)obj, &memguard_fifo_pool[numpgs - 1]);
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if (flags & M_ZERO)
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bzero(obj, PAGE_SIZE);
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bzero(obj, PAGE_SIZE * numpgs);
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} else {
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MEMGUARD_CRIT_SECTION_ENTER;
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memguard_mapused -= PAGE_SIZE;
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memguard_mapused -= (PAGE_SIZE * numpgs);
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MEMGUARD_CRIT_SECTION_EXIT;
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}
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return obj;
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@ -179,20 +203,39 @@ void
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memguard_free(void *addr)
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{
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struct memguard_entry *e;
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struct memguard_fifo *mgfifo;
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int idx;
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int *temp;
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memguard_guard(addr);
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addr = (void *)trunc_page((unsigned long)addr);
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/*
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* Page should not be guarded by now, so force a write.
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* The purpose of this is to increase the likelihood of catching a
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* double-free, but not necessarily a tamper-after-free (the second
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* thread freeing might not write before freeing, so this forces it
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* to and, subsequently, trigger a fault).
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*/
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temp = (int *)((unsigned long)addr + (PAGE_SIZE/2)); /* in page */
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*temp = 0xd34dc0d3;
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mgfifo = vtomgfifo((vm_offset_t)addr);
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idx = mgfifo->index;
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memguard_guard(addr, idx + 1);
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e = malloc(sizeof(struct memguard_entry), M_TEMP, M_NOWAIT);
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if (e == NULL) {
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MEMGUARD_CRIT_SECTION_ENTER;
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memguard_mapused -= PAGE_SIZE;
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memguard_mapused -= (PAGE_SIZE * (idx + 1));
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MEMGUARD_CRIT_SECTION_EXIT;
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kmem_free(memguard_map, (vm_offset_t)trunc_page(
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(unsigned long)addr), PAGE_SIZE);
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memguard_unguard(addr, idx + 1); /* just in case */
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vclrmgfifo((vm_offset_t)addr);
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kmem_free(memguard_map, (vm_offset_t)addr,
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PAGE_SIZE * (idx + 1));
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return;
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}
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e->ptr = (void *)trunc_page((unsigned long)addr);
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e->ptr = addr;
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MEMGUARD_CRIT_SECTION_ENTER;
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STAILQ_INSERT_TAIL(&memguard_fifo_pool, e, entries);
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STAILQ_INSERT_TAIL(mgfifo, e, entries);
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MEMGUARD_CRIT_SECTION_EXIT;
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}
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@ -201,11 +244,13 @@ memguard_free(void *addr)
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* future writes to it fail).
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*/
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static void
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memguard_guard(void *addr)
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memguard_guard(void *addr, int numpgs)
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{
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void *a = (void *)trunc_page((unsigned long)addr);
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(void)vm_map_protect(memguard_map, (vm_offset_t)a,
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(vm_offset_t)((unsigned long)a + PAGE_SIZE), VM_PROT_READ, 0);
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if (vm_map_protect(memguard_map, (vm_offset_t)a,
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(vm_offset_t)((unsigned long)a + (PAGE_SIZE * numpgs)),
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VM_PROT_READ, FALSE) != KERN_SUCCESS)
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panic("MEMGUARD: Unable to guard page!");
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}
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/*
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@ -213,10 +258,62 @@ memguard_guard(void *addr)
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* allow full data access).
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*/
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static void
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memguard_unguard(void *addr)
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memguard_unguard(void *addr, int numpgs)
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{
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void *a = (void *)trunc_page((unsigned long)addr);
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(void)vm_map_protect(memguard_map, (vm_offset_t)a,
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(vm_offset_t)((unsigned long)a + PAGE_SIZE),
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VM_PROT_READ | VM_PROT_WRITE, 0);
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if (vm_map_protect(memguard_map, (vm_offset_t)a,
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(vm_offset_t)((unsigned long)a + (PAGE_SIZE * numpgs)),
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VM_PROT_DEFAULT, FALSE) != KERN_SUCCESS)
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panic("MEMGUARD: Unable to unguard page!");
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}
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/*
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* vtomgfifo() converts a virtual address of the first page allocated for
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* an item to a memguard_fifo_pool reference for the corresponding item's
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* size.
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*
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* vsetmgfifo() sets a reference in an underlying page for the specified
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* virtual address to an appropriate memguard_fifo_pool.
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*
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* These routines are very similar to those defined by UMA in uma_int.h
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*/
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static struct memguard_fifo *
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vtomgfifo(vm_offset_t va)
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{
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vm_page_t p;
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struct memguard_fifo *mgfifo;
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p = PHYS_TO_VM_PAGE(pmap_kextract(va));
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mgfifo = (struct memguard_fifo *)p->object;
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/*
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* We use PG_SLAB, just like UMA does, even though we stash a
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* reference to a memguard_fifo, and not a slab.
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*/
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if ((p->flags & PG_SLAB) == 0)
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panic("MEMGUARD: Expected memguard_fifo reference to be set!");
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return mgfifo;
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}
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static void
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vsetmgfifo(vm_offset_t va, struct memguard_fifo *mgfifo)
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{
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vm_page_t p;
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p = PHYS_TO_VM_PAGE(pmap_kextract(va));
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p->object = (vm_object_t)mgfifo;
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/*
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* We use PG_SLAB, just like UMA does, even though we stash a reference
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* to a memguard_fifo, and not a slab.
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*/
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p->flags |= PG_SLAB;
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}
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static void vclrmgfifo(vm_offset_t va)
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{
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vm_page_t p;
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p = PHYS_TO_VM_PAGE(pmap_kextract(va));
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p->object = NULL;
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p->flags &= ~PG_SLAB;
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}
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