linux-kernel - Re: [PATCH] MIPS: BPF: Add support for SKF_AD

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Message-ID: <20170313105659.GJ996@jhogan-linux.le.imgtec.org>
Date:   Mon, 13 Mar 2017 10:56:59 +0000
From:   James Hogan <james.hogan@...tec.com>
To:     David Daney <david.daney@...ium.com>
CC:     <linux-mips@...ux-mips.org>, <ralf@...ux-mips.org>,
        <linux-kernel@...r.kernel.org>,
        "Steven J. Hill" <steven.hill@...ium.com>,
        Alexei Starovoitov <ast@...nel.org>, <netdev@...r.kernel.org>
Subject: Re: [PATCH] MIPS: BPF: Add support for SKF_AD_HATYPE

On Fri, Mar 10, 2017 at 02:14:05PM -0800, David Daney wrote:
> This let's us pass some additional "modprobe test-bpf" tests.
> 
> Reuse the code for SKF_AD_IFINDEX, but substitute the offset and size
> of the "type" field.
> 
> Signed-off-by: David Daney <david.daney@...ium.com>

I think the BPF maintainers should probably be Cc'd on this patch.
Cc'ing now.

> ---
>  arch/mips/net/bpf_jit.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/mips/net/bpf_jit.c b/arch/mips/net/bpf_jit.c
> index 49a2e22..f613708 100644
> --- a/arch/mips/net/bpf_jit.c
> +++ b/arch/mips/net/bpf_jit.c
> @@ -1111,6 +1111,7 @@ static int build_body(struct jit_ctx *ctx)
>  			emit_load(r_A, 28, off, ctx);
>  			break;
>  		case BPF_ANC | SKF_AD_IFINDEX:
> +		case BPF_ANC | SKF_AD_HATYPE:
>  			/* A = skb->dev->ifindex */

this comment should probably be updated.

>  			ctx->flags |= SEEN_SKB | SEEN_A;
>  			off = offsetof(struct sk_buff, dev);
> @@ -1120,10 +1121,15 @@ static int build_body(struct jit_ctx *ctx)
>  			emit_bcond(MIPS_COND_EQ, r_s0, r_zero,
>  				   b_imm(prog->len, ctx), ctx);
>  			emit_reg_move(r_ret, r_zero, ctx);
> -			BUILD_BUG_ON(FIELD_SIZEOF(struct net_device,
> -						  ifindex) != 4);
> -			off = offsetof(struct net_device, ifindex);
> -			emit_load(r_A, r_s0, off, ctx);
> +			if (code == (BPF_ANC | SKF_AD_IFINDEX)) {
> +				BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, ifindex) != 4);
> +				off = offsetof(struct net_device, ifindex);
> +				emit_load(r_A, r_s0, off, ctx);
> +			} else { /* (code == (BPF_ANC | SKF_AD_HATYPE) */
> +				BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, type) != 2);
> +				off = offsetof(struct net_device, type);
> +				emit_half_load(r_A, r_s0, off, ctx);

Technically net_device::type is unsigned, and emit_half_load uses LH
which sign extends. Does that matter in practice.

Cheers
James

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