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

[Pu Lehui]

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 at 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;
         }
}
```