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diff --git a/sys/vm/vm_map.h b/sys/vm/vm_map.h
--- a/sys/vm/vm_map.h
+++ b/sys/vm/vm_map.h
@@ -97,6 +97,10 @@
* a VM object (or sharing map) and offset into that object,
* and user-exported inheritance and protection information.
* Also included is control information for virtual copy operations.
+ *
+ * For stack gap map entries (MAP_ENTRY_GUARD | MAP_ENTRY_GROWS_DOWN
+ * or UP), the next_read member is reused as the stack_guard_page
+ * storage, and offset is the stack protection.
*/
struct vm_map_entry {
struct vm_map_entry *left; /* left child or previous entry */
diff --git a/sys/vm/vm_map.c b/sys/vm/vm_map.c
--- a/sys/vm/vm_map.c
+++ b/sys/vm/vm_map.c
@@ -4493,7 +4493,7 @@
vm_map_stack_locked(vm_map_t map, vm_offset_t addrbos, vm_size_t max_ssize,
vm_size_t growsize, vm_prot_t prot, vm_prot_t max, int cow)
{
- vm_map_entry_t new_entry, prev_entry;
+ vm_map_entry_t gap_entry, new_entry, prev_entry;
vm_offset_t bot, gap_bot, gap_top, top;
vm_size_t init_ssize, sgp;
int orient, rv;
@@ -4575,11 +4575,14 @@
* read-ahead logic is never used for it. Re-use
* next_read of the gap entry to store
* stack_guard_page for vm_map_growstack().
+ * Similarly, since a gap cannot have a backing object,
+ * store the original stack protections in the
+ * object offset.
*/
- if (orient == MAP_STACK_GROWS_DOWN)
- vm_map_entry_pred(new_entry)->next_read = sgp;
- else
- vm_map_entry_succ(new_entry)->next_read = sgp;
+ gap_entry = orient == MAP_STACK_GROWS_DOWN ?
+ vm_map_entry_pred(new_entry) : vm_map_entry_succ(new_entry);
+ gap_entry->next_read = sgp;
+ gap_entry->offset = prot;
} else {
(void)vm_map_delete(map, bot, top);
}
@@ -4599,6 +4602,7 @@
struct ucred *cred;
vm_offset_t gap_end, gap_start, grow_start;
vm_size_t grow_amount, guard, max_grow;
+ vm_prot_t prot;
rlim_t lmemlim, stacklim, vmemlim;
int rv, rv1 __diagused;
bool gap_deleted, grow_down, is_procstack;
@@ -4739,6 +4743,12 @@
}
if (grow_down) {
+ /*
+ * The gap_entry "offset" field is overloaded. See
+ * vm_map_stack_locked().
+ */
+ prot = gap_entry->offset;
+
grow_start = gap_entry->end - grow_amount;
if (gap_entry->start + grow_amount == gap_entry->end) {
gap_start = gap_entry->start;
@@ -4751,9 +4761,7 @@
gap_deleted = false;
}
rv = vm_map_insert(map, NULL, 0, grow_start,
- grow_start + grow_amount,
- stack_entry->protection, stack_entry->max_protection,
- MAP_STACK_GROWS_DOWN);
+ grow_start + grow_amount, prot, prot, MAP_STACK_GROWS_DOWN);
if (rv != KERN_SUCCESS) {
if (gap_deleted) {
rv1 = vm_map_insert(map, NULL, 0, gap_start,

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