Re: [PATCH 1/2] bpf, riscv: fix bugs in JIT for 32-bit ALU operations

[Song Liu]

On Thu, May 30, 2019 at 12:09 PM Luke Nelson <luke.r.nels@xxxxxxxxx> wrote:
>
> In BPF, 32-bit ALU operations should zero-extend their results into
> the 64-bit registers.  The current BPF JIT on RISC-V emits incorrect
> instructions that perform either sign extension only (e.g., addw/subw)
> or no extension on 32-bit add, sub, and, or, xor, lsh, rsh, arsh,
> and neg.  This behavior diverges from the interpreter and JITs for
> other architectures.
>
> This patch fixes the bugs by performing zero extension on the destination
> register of 32-bit ALU operations.
>
> Fixes: 2353ecc6f91f ("bpf, riscv: add BPF JIT for RV64G")
> Cc: Xi Wang <xi.wang@xxxxxxxxx>
> Signed-off-by: Luke Nelson <luke.r.nels@xxxxxxxxx>

This is a little messy. How about we introduce some helper function
like:

/* please find a better name... */
emit_32_or_64(bool is64, const u32 insn_32, const u32 inst_64, struct
rv_jit_context *ctx)
{
       if (is64)
            emit(insn_64, ctx);
       else {
            emit(insn_32, ctx);
           rd = xxxx;
           emit_zext_32(rd, ctx);
       }
}

Thanks,
Song

> ---
>  arch/riscv/net/bpf_jit_comp.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/arch/riscv/net/bpf_jit_comp.c b/arch/riscv/net/bpf_jit_comp.c
> index 80b12aa5e10d..426d5c33ea90 100644
> --- a/arch/riscv/net/bpf_jit_comp.c
> +++ b/arch/riscv/net/bpf_jit_comp.c
> @@ -751,22 +751,32 @@ static int emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>         case BPF_ALU | BPF_ADD | BPF_X:
>         case BPF_ALU64 | BPF_ADD | BPF_X:
>                 emit(is64 ? rv_add(rd, rd, rs) : rv_addw(rd, rd, rs), ctx);
> +               if (!is64)
> +                       emit_zext_32(rd, ctx);
>                 break;
>         case BPF_ALU | BPF_SUB | BPF_X:
>         case BPF_ALU64 | BPF_SUB | BPF_X:
>                 emit(is64 ? rv_sub(rd, rd, rs) : rv_subw(rd, rd, rs), ctx);
> +               if (!is64)
> +                       emit_zext_32(rd, ctx);
>                 break;
>         case BPF_ALU | BPF_AND | BPF_X:
>         case BPF_ALU64 | BPF_AND | BPF_X:
>                 emit(rv_and(rd, rd, rs), ctx);
> +               if (!is64)
> +                       emit_zext_32(rd, ctx);
>                 break;
>         case BPF_ALU | BPF_OR | BPF_X:
>         case BPF_ALU64 | BPF_OR | BPF_X:
>                 emit(rv_or(rd, rd, rs), ctx);
> +               if (!is64)
> +                       emit_zext_32(rd, ctx);
>                 break;
>         case BPF_ALU | BPF_XOR | BPF_X:
>         case BPF_ALU64 | BPF_XOR | BPF_X:
>                 emit(rv_xor(rd, rd, rs), ctx);
> +               if (!is64)
> +                       emit_zext_32(rd, ctx);
>                 break;
>         case BPF_ALU | BPF_MUL | BPF_X:
>         case BPF_ALU64 | BPF_MUL | BPF_X:
> @@ -789,14 +799,20 @@ static int emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>         case BPF_ALU | BPF_LSH | BPF_X:
>         case BPF_ALU64 | BPF_LSH | BPF_X:
>                 emit(is64 ? rv_sll(rd, rd, rs) : rv_sllw(rd, rd, rs), ctx);
> +               if (!is64)
> +                       emit_zext_32(rd, ctx);
>                 break;
>         case BPF_ALU | BPF_RSH | BPF_X:
>         case BPF_ALU64 | BPF_RSH | BPF_X:
>                 emit(is64 ? rv_srl(rd, rd, rs) : rv_srlw(rd, rd, rs), ctx);
> +               if (!is64)
> +                       emit_zext_32(rd, ctx);
>                 break;
>         case BPF_ALU | BPF_ARSH | BPF_X:
>         case BPF_ALU64 | BPF_ARSH | BPF_X:
>                 emit(is64 ? rv_sra(rd, rd, rs) : rv_sraw(rd, rd, rs), ctx);
> +               if (!is64)
> +                       emit_zext_32(rd, ctx);
>                 break;
>
>         /* dst = -dst */
> @@ -804,6 +820,8 @@ static int emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>         case BPF_ALU64 | BPF_NEG:
>                 emit(is64 ? rv_sub(rd, RV_REG_ZERO, rd) :
>                      rv_subw(rd, RV_REG_ZERO, rd), ctx);
> +               if (!is64)
> +                       emit_zext_32(rd, ctx);
>                 break;
>
>         /* dst = BSWAP##imm(dst) */
> @@ -958,14 +976,20 @@ static int emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>         case BPF_ALU | BPF_LSH | BPF_K:
>         case BPF_ALU64 | BPF_LSH | BPF_K:
>                 emit(is64 ? rv_slli(rd, rd, imm) : rv_slliw(rd, rd, imm), ctx);
> +               if (!is64)
> +                       emit_zext_32(rd, ctx);
>                 break;
>         case BPF_ALU | BPF_RSH | BPF_K:
>         case BPF_ALU64 | BPF_RSH | BPF_K:
>                 emit(is64 ? rv_srli(rd, rd, imm) : rv_srliw(rd, rd, imm), ctx);
> +               if (!is64)
> +                       emit_zext_32(rd, ctx);
>                 break;
>         case BPF_ALU | BPF_ARSH | BPF_K:
>         case BPF_ALU64 | BPF_ARSH | BPF_K:
>                 emit(is64 ? rv_srai(rd, rd, imm) : rv_sraiw(rd, rd, imm), ctx);
> +               if (!is64)
> +                       emit_zext_32(rd, ctx);
>                 break;
>
>         /* JUMP off */
> --
> 2.19.1
>