[PATCH bpf-next v1 1/2] bpf: Disallow calling bpf_obj_new_impl on bpf_mem_alloc_init failure

[Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>]

Instead of checking bpf_global_ma_set at runtime on each allocation
inside bpf_obj_new_impl, simply disallow calling the kfunc in case
bpf_global_ma initialization failed during program verification.

The error generated when bpf_global_ma initialization fails:
...
21: (18) r1 = 0x7                     ; R1_w=7
23: (b7) r2 = 0                       ; R2_w=0
24: (85) call bpf_obj_new_impl#36585
bpf_global_ma initialization failed, can't call bpf_obj_new_impl
calling kernel function bpf_obj_new_impl is not allowed

Suggested-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
---
 kernel/bpf/helpers.c  |  2 --
 kernel/bpf/verifier.c | 13 ++++++++++++-
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 212e791d7452..bc02f55adc1f 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1760,8 +1760,6 @@ void *bpf_obj_new_impl(u64 local_type_id__k, void *meta__ign)
 	u64 size = local_type_id__k;
 	void *p;
 
-	if (unlikely(!bpf_global_ma_set))
-		return NULL;
 	p = bpf_mem_alloc(&bpf_global_ma, size);
 	if (!p)
 		return NULL;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 195d24316750..f04bee7934a8 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8746,6 +8746,17 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 	return 0;
 }
 
+static bool is_kfunc_disabled(struct bpf_verifier_env *env, const struct btf *btf, u32 func_id)
+{
+	if (btf != btf_vmlinux)
+		return false;
+	if (!bpf_global_ma_set && func_id == special_kfunc_list[KF_bpf_obj_new_impl]) {
+		verbose(env, "bpf_global_ma initialization failed, can't call bpf_obj_new_impl\n");
+		return true;
+	}
+	return false;
+}
+
 static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 			    int *insn_idx_p)
 {
@@ -8773,7 +8784,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 	func_proto = btf_type_by_id(desc_btf, func->type);
 
 	kfunc_flags = btf_kfunc_id_set_contains(desc_btf, resolve_prog_type(env->prog), func_id);
-	if (!kfunc_flags) {
+	if (!kfunc_flags || is_kfunc_disabled(env, desc_btf, func_id)) {
 		verbose(env, "calling kernel function %s is not allowed\n",
 			func_name);
 		return -EACCES;
-- 
2.38.1