Re: [PATCH bpf-next 1/8] bpf/verifier: Handle BPF_LOAD_ACQ instructions in insn_def_regno()

From: Peilin Ye <yepeilin@google.com>
To: Pu Lehui <pulehui@huawei.com>
Cc: bpf@vger.kernel.org, linux-riscv@lists.infradead.org,
	"Andrea Parri" <parri.andrea@gmail.com>,
	"Björn Töpel" <bjorn@kernel.org>,
	"Puranjay Mohan" <puranjay@kernel.org>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Andrii Nakryiko" <andrii@kernel.org>,
	"Martin KaFai Lau" <martin.lau@linux.dev>,
	"Eduard Zingerman" <eddyz87@gmail.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	"Song Liu" <song@kernel.org>,
	"Yonghong Song" <yonghong.song@linux.dev>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"KP Singh" <kpsingh@kernel.org>,
	"Stanislav Fomichev" <sdf@fomichev.me>,
	"Hao Luo" <haoluo@google.com>, "Jiri Olsa" <jolsa@kernel.org>,
	"Luke Nelson" <luke.r.nels@gmail.com>,
	"Xi Wang" <xi.wang@gmail.com>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Alexandre Ghiti" <alex@ghiti.fr>,
	"Mykola Lysenko" <mykolal@fb.com>,
	"Shuah Khan" <shuah@kernel.org>, "Josh Don" <joshdon@google.com>,
	"Barret Rhoden" <brho@google.com>,
	"Neel Natu" <neelnatu@google.com>,
	"Benjamin Segall" <bsegall@google.com>
Subject: Re: [PATCH bpf-next 1/8] bpf/verifier: Handle BPF_LOAD_ACQ instructions in insn_def_regno()
Date: Wed, 7 May 2025 00:18:43 +0000	[thread overview]
Message-ID: <aBqm4-CsZyWXRwp_@google.com> (raw)
In-Reply-To: <83698e73-3b47-4cdc-af50-c4f3ca479b7a@huawei.com>

Hi Lehui,

On Tue, May 06, 2025 at 10:03:59PM +0800, Pu Lehui wrote:
> On 2025/4/30 8:50, Peilin Ye wrote:
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -3649,13 +3649,16 @@ static int insn_def_regno(const struct bpf_insn *insn)
> >   	case BPF_ST:
> >   		return -1;
> >   	case BPF_STX:
> > -		if ((BPF_MODE(insn->code) == BPF_ATOMIC ||
> > -		     BPF_MODE(insn->code) == BPF_PROBE_ATOMIC) &&
> > -		    (insn->imm & BPF_FETCH)) {
> > +		if (BPF_MODE(insn->code) == BPF_ATOMIC ||
> > +		    BPF_MODE(insn->code) == BPF_PROBE_ATOMIC) {
> >   			if (insn->imm == BPF_CMPXCHG)
> >   				return BPF_REG_0;
> > -			else
> > +			else if (insn->imm == BPF_LOAD_ACQ)
> > +				return insn->dst_reg;
> > +			else if (insn->imm & BPF_FETCH)
> >   				return insn->src_reg;
> > +			else
> > +				return -1;
> >   		} else {
> >   			return -1;
> >   		}
> 
> How about simplify like this:
> ```
> static int insn_def_regno(const struct bpf_insn *insn)
> {
>         switch (BPF_CLASS(insn->code)) {
>         case BPF_JMP:
>         case BPF_JMP32:
>         case BPF_ST:
>                 return -1;
>         case BPF_STX:
>                 if (BPF_MODE(insn->code) == BPF_ATOMIC ||
>                     BPF_MODE(insn->code) == BPF_PROBE_ATOMIC) {
>                         if (insn->imm == BPF_CMPXCHG)
>                                 return BPF_REG_0;
>                         else if (insn->imm == BPF_LOAD_ACQ)
>                                 return insn->dst_reg;
>                         else if (insn->imm & BPF_FETCH)
>                                 return insn->src_reg;
>                 }
>                 return -1;
>         default:
>                 return insn->dst_reg;
>         }
> }
> ```

I see, I'll change it in v2.  Thanks for the suggestion!

Peilin Ye