Re: [PATCH bpf v2] bpf, riscv: clear high 32 bits for ALU32 add/sub/neg/lsh/rsh/arsh

[Palmer Dabbelt]

On Thu, 30 May 2019 15:29:22 PDT (-0700), 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
> sign extension only (e.g., addw, subw) on 32-bit add, sub, 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>

Reviewed-by: Palmer Dabbelt <palmer@xxxxxxxxxx>

Thanks!  I'm assuming this is going in through a BPF tree and not the RISC-V
tree, but LMK if that's not the case.

> ---
> The original patch is
> https://lkml.org/lkml/2019/5/30/1370
>
> This version is rebased against the bpf tree.
> ---
>  arch/riscv/net/bpf_jit_comp.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/arch/riscv/net/bpf_jit_comp.c b/arch/riscv/net/bpf_jit_comp.c
> index e5c8d675bd6e..426d5c33ea90 100644
> --- a/arch/riscv/net/bpf_jit_comp.c
> +++ b/arch/riscv/net/bpf_jit_comp.c
> @@ -751,10 +751,14 @@ 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:
> @@ -795,14 +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 */
> @@ -810,6 +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) */
> @@ -964,14 +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 */