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

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Message-ID: <20231208203535.GG36716@noisy.programming.kicks-ass.net>
Date: Fri, 8 Dec 2023 21:35:35 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Jiri Olsa <olsajiri@...il.com>, Song Liu <song@...nel.org>,
	Song Liu <songliubraving@...a.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, X86 ML <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"David S. Miller" <davem@...emloft.net>,
	David Ahern <dsahern@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>, Arnd Bergmann <arnd@...db.de>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Kees Cook <keescook@...omium.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	linux-riscv <linux-riscv@...ts.infradead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	bpf <bpf@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>,
	clang-built-linux <llvm@...ts.linux.dev>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Joao Moreira <joao@...rdrivepizza.com>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v2 2/2] x86/cfi,bpf: Fix BPF JIT call

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