bpf: Refactor kptr_off_tab into btf_record

To prepare the BPF verifier to handle special fields in both map values
and program allocated types coming from program BTF, we need to refactor
the kptr_off_tab handling code into something more generic and reusable
across both cases to avoid code duplication.

Later patches also require passing this data to helpers at runtime, so
that they can work on user defined types, initialize them, destruct
them, etc.

The main observation is that both map values and such allocated types
point to a type in program BTF, hence they can be handled similarly. We
can prepare a field metadata table for both cases and store them in
struct bpf_map or struct btf depending on the use case.

Hence, refactor the code into generic btf_record and btf_field member
structs. The btf_record represents the fields of a specific btf_type in
user BTF. The cnt indicates the number of special fields we successfully
recognized, and field_mask is a bitmask of fields that were found, to
enable quick determination of availability of a certain field.

Subsequently, refactor the rest of the code to work with these generic
types, remove assumptions about kptr and kptr_off_tab, rename variables
to more meaningful names, etc.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20221103191013.1236066-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 6 insertions, 7 deletions

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 832b2659e96e..417f84342e98 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -310,8 +310,7 @@ static void check_and_free_fields(struct bpf_array *arr, void *val)
 {
 	if (map_value_has_timer(&arr->map))
 		bpf_timer_cancel_and_free(val + arr->map.timer_off);
-	if (map_value_has_kptrs(&arr->map))
-		bpf_map_free_kptrs(&arr->map, val);
+	bpf_obj_free_fields(arr->map.record, val);
 }
 
 /* Called from syscall or from eBPF program */
@@ -409,7 +408,7 @@ static void array_map_free_timers(struct bpf_map *map)
 	struct bpf_array *array = container_of(map, struct bpf_array, map);
 	int i;
 
-	/* We don't reset or free kptr on uref dropping to zero. */
+	/* We don't reset or free fields other than timer on uref dropping to zero. */
 	if (!map_value_has_timer(map))
 		return;
 
@@ -423,22 +422,22 @@ static void array_map_free(struct bpf_map *map)
 	struct bpf_array *array = container_of(map, struct bpf_array, map);
 	int i;
 
-	if (map_value_has_kptrs(map)) {
+	if (!IS_ERR_OR_NULL(map->record)) {
 		if (array->map.map_type == BPF_MAP_TYPE_PERCPU_ARRAY) {
 			for (i = 0; i < array->map.max_entries; i++) {
 				void __percpu *pptr = array->pptrs[i & array->index_mask];
 				int cpu;
 
 				for_each_possible_cpu(cpu) {
-					bpf_map_free_kptrs(map, per_cpu_ptr(pptr, cpu));
+					bpf_obj_free_fields(map->record, per_cpu_ptr(pptr, cpu));
 					cond_resched();
 				}
 			}
 		} else {
 			for (i = 0; i < array->map.max_entries; i++)
-				bpf_map_free_kptrs(map, array_map_elem_ptr(array, i));
+				bpf_obj_free_fields(map->record, array_map_elem_ptr(array, i));
 		}
-		bpf_map_free_kptr_off_tab(map);
+		bpf_map_free_record(map);
 	}
 
 	if (array->map.map_type == BPF_MAP_TYPE_PERCPU_ARRAY)