Fix page fault in critical section in the slab allocator

* kern/slab.c (host_slab_info): Use wired kernel memory to build the
cache info.

1 files changed, 36 insertions, 28 deletions

diff --git a/kern/slab.c b/kern/slab.c
index 43962e7e..1f8e0005 100644
--- a/kern/slab.c
+++ b/kern/slab.c
@@ -1502,39 +1502,33 @@ kern_return_t host_slab_info(host_t host, cache_info_array_t *infop,
     struct kmem_cache *cache;
     cache_info_t *info;
     unsigned int i, nr_caches;
-    vm_size_t info_size = 0;
+    vm_size_t info_size;
     kern_return_t kr;
 
     if (host == HOST_NULL)
         return KERN_INVALID_HOST;
 
-    /*
-     * Assume the cache list is unaltered once the kernel is ready.
-     */
+    /* Assume the cache list is mostly unaltered once the kernel is ready */
 
-    simple_lock(&kmem_cache_list_lock);
+retry:
+    /* Harmless unsynchronized access, real value checked later */
     nr_caches = kmem_nr_caches;
-    simple_unlock(&kmem_cache_list_lock);
-
-    if (nr_caches <= *infoCntp)
-        info = *infop;
-    else {
-        vm_offset_t info_addr;
-
-        info_size = round_page(nr_caches * sizeof(*info));
-        kr = kmem_alloc_pageable(ipc_kernel_map, &info_addr, info_size);
-
-        if (kr != KERN_SUCCESS)
-            return kr;
-
-        info = (cache_info_t *)info_addr;
-    }
+    info_size = nr_caches * sizeof(*info);
+    info = (cache_info_t *)kalloc(info_size);
 
     if (info == NULL)
         return KERN_RESOURCE_SHORTAGE;
 
     i = 0;
 
+    simple_lock(&kmem_cache_list_lock);
+
+    if (nr_caches != kmem_nr_caches) {
+        simple_unlock(&kmem_cache_list_lock);
+        kfree((vm_offset_t)info, info_size);
+        goto retry;
+    }
+
     list_for_each_entry(&kmem_cache_list, cache, node) {
         simple_lock(&cache->lock);
         info[i].flags = cache->flags;
@@ -1559,24 +1553,38 @@ kern_return_t host_slab_info(host_t host, cache_info_array_t *infop,
         i++;
     }
 
-    if (info != *infop) {
+    simple_unlock(&kmem_cache_list_lock);
+
+    if (nr_caches <= *infoCntp) {
+        memcpy(*infop, info, info_size);
+    } else {
+        vm_offset_t info_addr;
+        vm_size_t total_size;
         vm_map_copy_t copy;
-        vm_size_t used;
 
-        used = nr_caches * sizeof(*info);
+        kr = kmem_alloc_pageable(ipc_kernel_map, &info_addr, info_size);
+
+        if (kr != KERN_SUCCESS)
+            goto out;
 
-        if (used != info_size)
-            memset((char *)info + used, 0, info_size - used);
+        memcpy((char *)info_addr, info, info_size);
+        total_size = round_page(info_size);
 
-        kr = vm_map_copyin(ipc_kernel_map, (vm_offset_t)info, used, TRUE,
-                           &copy);
+        if (info_size < total_size)
+            memset((char *)(info_addr + info_size),
+                   0, total_size - info_size);
 
+        kr = vm_map_copyin(ipc_kernel_map, info_addr, info_size, TRUE, &copy);
         assert(kr == KERN_SUCCESS);
         *infop = (cache_info_t *)copy;
     }
 
     *infoCntp = nr_caches;
+    kr = KERN_SUCCESS;
+
+out:
+    kfree((vm_offset_t)info, info_size);
 
-    return KERN_SUCCESS;
+    return kr;
 }
 #endif /* MACH_DEBUG */