bpf: fix potential 32-bit overflow when accessing ARRAY map element

If BPF array map is bigger than 4GB, element pointer calculation can
overflow because both index and elem_size are u32. Fix this everywhere
by forcing 64-bit multiplication. Extract this formula into separate
small helper and use it consistently in various places.

Speculative-preventing formula utilizing index_mask trick is left as is,
but explicit u64 casts are added in both places.

Fixes: c85d6913 ("bpf: move memory size checks to bpf_map_charge_init()")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20220715053146.1291891-2-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/arraymap.c

@@ -156,6 +156,11 @@ static struct bpf_map *array_map_alloc(union bpf_attr *attr)
 	return &array->map;
 }
 
+static void *array_map_elem_ptr(struct bpf_array* array, u32 index)
+{
+	return array->value + (u64)array->elem_size * index;
+}
+
 /* Called from syscall or from eBPF program */
 static void *array_map_lookup_elem(struct bpf_map *map, void *key)
 {
@@ -165,7 +170,7 @@ static void *array_map_lookup_elem(struct bpf_map *map, void *key)
 	if (unlikely(index >= array->map.max_entries))
 		return NULL;
 
-	return array->value + array->elem_size * (index & array->index_mask);
+	return array->value + (u64)array->elem_size * (index & array->index_mask);
 }
 
 static int array_map_direct_value_addr(const struct bpf_map *map, u64 *imm,
@@ -339,7 +344,7 @@ static int array_map_update_elem(struct bpf_map *map, void *key, void *value,
 		       value, map->value_size);
 	} else {
 		val = array->value +
-			array->elem_size * (index & array->index_mask);
+			(u64)array->elem_size * (index & array->index_mask);
 		if (map_flags & BPF_F_LOCK)
 			copy_map_value_locked(map, val, value, false);
 		else
@@ -408,8 +413,7 @@ static void array_map_free_timers(struct bpf_map *map)
 		return;
 
 	for (i = 0; i < array->map.max_entries; i++)
-		bpf_timer_cancel_and_free(array->value + array->elem_size * i +
-					  map->timer_off);
+		bpf_timer_cancel_and_free(array_map_elem_ptr(array, i) + map->timer_off);
 }
 
 /* Called when map->refcnt goes to zero, either from workqueue or from syscall */
@@ -420,7 +424,7 @@ static void array_map_free(struct bpf_map *map)
 
 	if (map_value_has_kptrs(map)) {
 		for (i = 0; i < array->map.max_entries; i++)
-			bpf_map_free_kptrs(map, array->value + array->elem_size * i);
+			bpf_map_free_kptrs(map, array_map_elem_ptr(array, i));
 		bpf_map_free_kptr_off_tab(map);
 	}
 
@@ -556,7 +560,7 @@ static void *bpf_array_map_seq_start(struct seq_file *seq, loff_t *pos)
 	index = info->index & array->index_mask;
 	if (info->percpu_value_buf)
 	       return array->pptrs[index];
-	return array->value + array->elem_size * index;
+	return array_map_elem_ptr(array, index);
 }
 
 static void *bpf_array_map_seq_next(struct seq_file *seq, void *v, loff_t *pos)
@@ -575,7 +579,7 @@ static void *bpf_array_map_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 	index = info->index & array->index_mask;
 	if (info->percpu_value_buf)
 	       return array->pptrs[index];
-	return array->value + array->elem_size * index;
+	return array_map_elem_ptr(array, index);
 }
 
 static int __bpf_array_map_seq_show(struct seq_file *seq, void *v)
@@ -690,7 +694,7 @@ static int bpf_for_each_array_elem(struct bpf_map *map, bpf_callback_t callback_
 		if (is_percpu)
 			val = this_cpu_ptr(array->pptrs[i]);
 		else
-			val = array->value + array->elem_size * i;
+			val = array_map_elem_ptr(array, i);
 		num_elems++;
 		key = i;
 		ret = callback_fn((u64)(long)map, (u64)(long)&key,