bpf: Refactor trampoline update code

As we need to introduce a third type of attachment for trampolines, the
flattened signature of arch_prepare_bpf_trampoline gets even more
complicated.

Refactor the prog and count argument to arch_prepare_bpf_trampoline to
use bpf_tramp_progs to simplify the addition and accounting for new
attachment types.

Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200304191853.1529-2-kpsingh@chromium.org

2 files changed, 44 insertions, 28 deletions

diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index c498f0fffb40..ca5cc8cdb6eb 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -320,6 +320,7 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 	struct bpf_struct_ops_value *uvalue, *kvalue;
 	const struct btf_member *member;
 	const struct btf_type *t = st_ops->type;
+	struct bpf_tramp_progs *tprogs = NULL;
 	void *udata, *kdata;
 	int prog_fd, err = 0;
 	void *image;
@@ -343,6 +344,10 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 	if (uvalue->state || refcount_read(&uvalue->refcnt))
 		return -EINVAL;
 
+	tprogs = kcalloc(BPF_TRAMP_MAX, sizeof(*tprogs), GFP_KERNEL);
+	if (!tprogs)
+		return -ENOMEM;
+
 	uvalue = (struct bpf_struct_ops_value *)st_map->uvalue;
 	kvalue = (struct bpf_struct_ops_value *)&st_map->kvalue;
 
@@ -425,10 +430,12 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 			goto reset_unlock;
 		}
 
+		tprogs[BPF_TRAMP_FENTRY].progs[0] = prog;
+		tprogs[BPF_TRAMP_FENTRY].nr_progs = 1;
 		err = arch_prepare_bpf_trampoline(image,
 						  st_map->image + PAGE_SIZE,
 						  &st_ops->func_models[i], 0,
-						  &prog, 1, NULL, 0, NULL);
+						  tprogs, NULL);
 		if (err < 0)
 			goto reset_unlock;
 
@@ -469,6 +476,7 @@ reset_unlock:
 	memset(uvalue, 0, map->value_size);
 	memset(kvalue, 0, map->value_size);
 unlock:
+	kfree(tprogs);
 	mutex_unlock(&st_map->lock);
 	return err;
 }
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 704fa787fec0..546198f6f307 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -190,40 +190,49 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
 	return ret;
 }
 
-/* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
- * bytes on x86.  Pick a number to fit into BPF_IMAGE_SIZE / 2
- */
-#define BPF_MAX_TRAMP_PROGS 40
+static struct bpf_tramp_progs *
+bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total)
+{
+	const struct bpf_prog_aux *aux;
+	struct bpf_tramp_progs *tprogs;
+	struct bpf_prog **progs;
+	int kind;
+
+	*total = 0;
+	tprogs = kcalloc(BPF_TRAMP_MAX, sizeof(*tprogs), GFP_KERNEL);
+	if (!tprogs)
+		return ERR_PTR(-ENOMEM);
+
+	for (kind = 0; kind < BPF_TRAMP_MAX; kind++) {
+		tprogs[kind].nr_progs = tr->progs_cnt[kind];
+		*total += tr->progs_cnt[kind];
+		progs = tprogs[kind].progs;
+
+		hlist_for_each_entry(aux, &tr->progs_hlist[kind], tramp_hlist)
+			*progs++ = aux->prog;
+	}
+	return tprogs;
+}
 
 static int bpf_trampoline_update(struct bpf_trampoline *tr)
 {
 	void *old_image = tr->image + ((tr->selector + 1) & 1) * BPF_IMAGE_SIZE/2;
 	void *new_image = tr->image + (tr->selector & 1) * BPF_IMAGE_SIZE/2;
-	struct bpf_prog *progs_to_run[BPF_MAX_TRAMP_PROGS];
-	int fentry_cnt = tr->progs_cnt[BPF_TRAMP_FENTRY];
-	int fexit_cnt = tr->progs_cnt[BPF_TRAMP_FEXIT];
-	struct bpf_prog **progs, **fentry, **fexit;
+	struct bpf_tramp_progs *tprogs;
 	u32 flags = BPF_TRAMP_F_RESTORE_REGS;
-	struct bpf_prog_aux *aux;
-	int err;
+	int err, total;
 
-	if (fentry_cnt + fexit_cnt == 0) {
+	tprogs = bpf_trampoline_get_progs(tr, &total);
+	if (IS_ERR(tprogs))
+		return PTR_ERR(tprogs);
+
+	if (total == 0) {
 		err = unregister_fentry(tr, old_image);
 		tr->selector = 0;
 		goto out;
 	}
 
-	/* populate fentry progs */
-	fentry = progs = progs_to_run;
-	hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FENTRY], tramp_hlist)
-		*progs++ = aux->prog;
-
-	/* populate fexit progs */
-	fexit = progs;
-	hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FEXIT], tramp_hlist)
-		*progs++ = aux->prog;
-
-	if (fexit_cnt)
+	if (tprogs[BPF_TRAMP_FEXIT].nr_progs)
 		flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;
 
 	/* Though the second half of trampoline page is unused a task could be
@@ -232,12 +241,11 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
 	 * preempted task. Hence wait for tasks to voluntarily schedule or go
 	 * to userspace.
 	 */
+
 	synchronize_rcu_tasks();
 
 	err = arch_prepare_bpf_trampoline(new_image, new_image + BPF_IMAGE_SIZE / 2,
-					  &tr->func.model, flags,
-					  fentry, fentry_cnt,
-					  fexit, fexit_cnt,
+					  &tr->func.model, flags, tprogs,
 					  tr->func.addr);
 	if (err < 0)
 		goto out;
@@ -252,6 +260,7 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
 		goto out;
 	tr->selector++;
 out:
+	kfree(tprogs);
 	return err;
 }
 
@@ -409,8 +418,7 @@ void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start)
 int __weak
 arch_prepare_bpf_trampoline(void *image, void *image_end,
 			    const struct btf_func_model *m, u32 flags,
-			    struct bpf_prog **fentry_progs, int fentry_cnt,
-			    struct bpf_prog **fexit_progs, int fexit_cnt,
+			    struct bpf_tramp_progs *tprogs,
 			    void *orig_call)
 {
 	return -ENOTSUPP;