Re: [PATCH v2 2/2] x86/cfi,bpf: Fix BPF JIT call

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Dec 08, 2023 at 11:40:27AM -0800, Alexei Starovoitov wrote:

> typedef void (*btf_dtor_kfunc_t)(void *);
>         btf_dtor_kfunc_t dtor;
> but the bpf_cgroup_release takes 'struct cgroup*'.
> From kcfi pov void * == struct cgroup * ?
> Do we need to change it to 'void *cgrp' ?

Yes, doing that naively like the below, gets me lovely things like:

validate_case:FAIL:expect_msg unexpected error: -22
VERIFIER LOG:
=============
=============
EXPECTED MSG: 'Possibly NULL pointer passed to trusted arg0'
#48/7    cgrp_kfunc/cgrp_kfunc_acquire_untrusted:FAIL
run_subtest:PASS:obj_open_mem 0 nsec
libbpf: extern (func ksym) 'bpf_cgroup_release': func_proto [148] incompatible with vmlinux [125610]
libbpf: failed to load object 'cgrp_kfunc_failure'


But let me try rebuilding everything..


---
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index b3be5742d6f1..078b207af7f0 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2145,10 +2145,11 @@ __bpf_kfunc struct task_struct *bpf_task_acquire(struct task_struct *p)
  * bpf_task_release - Release the reference acquired on a task.
  * @p: The task on which a reference is being released.
  */
-__bpf_kfunc void bpf_task_release(struct task_struct *p)
+__bpf_kfunc void bpf_task_release(void *p)
 {
 	put_task_struct_rcu_user(p);
 }
+EXPORT_SYMBOL_GPL(bpf_task_release);
 
 #ifdef CONFIG_CGROUPS
 /**
@@ -2169,10 +2170,11 @@ __bpf_kfunc struct cgroup *bpf_cgroup_acquire(struct cgroup *cgrp)
  * drops to 0.
  * @cgrp: The cgroup on which a reference is being released.
  */
-__bpf_kfunc void bpf_cgroup_release(struct cgroup *cgrp)
+__bpf_kfunc void bpf_cgroup_release(void *cgrp)
 {
 	cgroup_put(cgrp);
 }
+EXPORT_SYMBOL_GPL(bpf_cgroup_release);
 
 /**
  * bpf_cgroup_ancestor - Perform a lookup on an entry in a cgroup's ancestor