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

From: Peter Zijlstra <peterz@infradead.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Jiri Olsa <olsajiri@gmail.com>, Song Liu <song@kernel.org>,
	Song Liu <songliubraving@meta.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	"David S. Miller" <davem@davemloft.net>,
	David Ahern <dsahern@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <martin.lau@linux.dev>,
	Yonghong Song <yonghong.song@linux.dev>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Sami Tolvanen <samitolvanen@google.com>,
	Kees Cook <keescook@chromium.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	bpf <bpf@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	clang-built-linux <llvm@lists.linux.dev>,
	Josh Poimboeuf <jpoimboe@kernel.org>,
	Joao Moreira <joao@overdrivepizza.com>,
	Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH v2 2/2] x86/cfi,bpf: Fix BPF JIT call
Date: Fri, 8 Dec 2023 21:35:35 +0100	[thread overview]
Message-ID: <20231208203535.GG36716@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <CAADnVQKsnZfFomQ4wTZz=jMZW5QCV2XiXVsi64bghHkAjJtcmA@mail.gmail.com>

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
