bpf: Replace callers of BPF_CAST_CALL with proper function typedef

In order to keep ahead of cases in the kernel where Control Flow
Integrity (CFI) may trip over function call casts, enabling
-Wcast-function-type is helpful. To that end, BPF_CAST_CALL causes
various warnings and is one of the last places in the kernel
triggering this warning.

For actual function calls, replace BPF_CAST_CALL() with a typedef, which
captures the same details about the given function pointers.

This change results in no object code difference.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://github.com/KSPP/linux/issues/20
Link: https://lore.kernel.org/lkml/CAEf4Bzb46=-J5Fxc3mMZ8JQPtK1uoE0q6+g6WPz53Cvx=CBEhw@mail.gmail.com
Link: https://lore.kernel.org/bpf/20210928230946.4062144-3-keescook@chromium.org

3 files changed, 8 insertions, 11 deletions

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index cebd4fb06d19..5e1ccfae916b 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -645,7 +645,7 @@ static const struct bpf_iter_seq_info iter_seq_info = {
 	.seq_priv_size		= sizeof(struct bpf_iter_seq_array_map_info),
 };
 
-static int bpf_for_each_array_elem(struct bpf_map *map, void *callback_fn,
+static int bpf_for_each_array_elem(struct bpf_map *map, bpf_callback_t callback_fn,
 				   void *callback_ctx, u64 flags)
 {
 	u32 i, key, num_elems = 0;
@@ -668,9 +668,8 @@ static int bpf_for_each_array_elem(struct bpf_map *map, void *callback_fn,
 			val = array->value + array->elem_size * i;
 		num_elems++;
 		key = i;
-		ret = BPF_CAST_CALL(callback_fn)((u64)(long)map,
-					(u64)(long)&key, (u64)(long)val,
-					(u64)(long)callback_ctx, 0);
+		ret = callback_fn((u64)(long)map, (u64)(long)&key,
+				  (u64)(long)val, (u64)(long)callback_ctx, 0);
 		/* return value: 0 - continue, 1 - stop and return */
 		if (ret)
 			break;
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 3d8f9d6997d5..d29af9988f37 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -2049,7 +2049,7 @@ static const struct bpf_iter_seq_info iter_seq_info = {
 	.seq_priv_size		= sizeof(struct bpf_iter_seq_hash_map_info),
 };
 
-static int bpf_for_each_hash_elem(struct bpf_map *map, void *callback_fn,
+static int bpf_for_each_hash_elem(struct bpf_map *map, bpf_callback_t callback_fn,
 				  void *callback_ctx, u64 flags)
 {
 	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
@@ -2089,9 +2089,8 @@ static int bpf_for_each_hash_elem(struct bpf_map *map, void *callback_fn,
 				val = elem->key + roundup_key_size;
 			}
 			num_elems++;
-			ret = BPF_CAST_CALL(callback_fn)((u64)(long)map,
-					(u64)(long)key, (u64)(long)val,
-					(u64)(long)callback_ctx, 0);
+			ret = callback_fn((u64)(long)map, (u64)(long)key,
+					  (u64)(long)val, (u64)(long)callback_ctx, 0);
 			/* return value: 0 - continue, 1 - stop and return */
 			if (ret) {
 				rcu_read_unlock();
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 2c604ff8c7fb..1ffd469c217f 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1056,7 +1056,7 @@ static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer)
 	struct bpf_hrtimer *t = container_of(hrtimer, struct bpf_hrtimer, timer);
 	struct bpf_map *map = t->map;
 	void *value = t->value;
-	void *callback_fn;
+	bpf_callback_t callback_fn;
 	void *key;
 	u32 idx;
 
@@ -1081,8 +1081,7 @@ static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer)
 		key = value - round_up(map->key_size, 8);
 	}
 
-	BPF_CAST_CALL(callback_fn)((u64)(long)map, (u64)(long)key,
-				   (u64)(long)value, 0, 0);
+	callback_fn((u64)(long)map, (u64)(long)key, (u64)(long)value, 0, 0);
 	/* The verifier checked that return value is zero. */
 
 	this_cpu_write(hrtimer_running, NULL);