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 18:21:52 +0100	[thread overview]
Message-ID: <20231208172152.GD36716@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20231208134041.GD28727@noisy.programming.kicks-ass.net>

On Fri, Dec 08, 2023 at 02:40:41PM +0100, Peter Zijlstra wrote:
> On Fri, Dec 08, 2023 at 11:29:40AM +0100, Peter Zijlstra wrote:
> > The only problem I now have is the one XXX, I'm not entirely sure what
> > signature to use there.
> 
> > @@ -119,6 +119,7 @@ int bpf_struct_ops_test_run(struct bpf_p
> >  	op_idx = prog->expected_attach_type;
> >  	err = bpf_struct_ops_prepare_trampoline(tlinks, link,
> >  						&st_ops->func_models[op_idx],
> > +						/* XXX */ NULL,
> >  						image, image + PAGE_SIZE);
> >  	if (err < 0)
> >  		goto out;
> 
> Duh, that should ofcourse be something of dummy_ops_test_ret_fn type.
> Let me go fix that.

Next one.. bpf_obj_free_fields: field->kptr.dtor(xchg_field);

The one that trips is bpf_cgroup_release().

objtool doesn't think the address of that function 'escapes' and
'helpfully' seals that function, and then BPF thinks it does escape and
manages the above indirect call and *boom*.

How can I tell which functions escape according to BPF such that I might
teach objtool this?