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

From: Pu Lehui <pulehui@huawei.com>
To: Peilin Ye <yepeilin@google.com>, <bpf@vger.kernel.org>
Cc: 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: Tue, 6 May 2025 22:03:59 +0800	[thread overview]
Message-ID: <83698e73-3b47-4cdc-af50-c4f3ca479b7a@huawei.com> (raw)
In-Reply-To: <2c1ec0e60974f8438730dc5126f9ed986b32a3f6.1745970908.git.yepeilin@google.com>


On 2025/4/30 8:50, Peilin Ye wrote:
> In preparation for supporting BPF load-acquire and store-release
> instructions for architectures where bpf_jit_needs_zext() returns true
> (e.g. riscv64), make insn_def_regno() handle load-acquires properly.
> 
> Signed-off-by: Peilin Ye <yepeilin@google.com>
> ---
>   kernel/bpf/verifier.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 54c6953a8b84..6435ea23fee4 100644
> --- 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;
         }
}
```

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