Subject: Re: [PATCH v2 net-next 3/3] ARM: net: bpf_jit_32: support BPF_S_ANC_SECCOMP_LD_W instruction

From: Daniel Borkmann <[email-masked]>
Date: Sat, 27 Apr 2013 08:27:17 +0200

On 04/27/2013 04:17 AM, Xi Wang wrote:
> This patch implements the seccomp BPF_S_ANC_SECCOMP_LD_W instruction
> in ARM JIT.
>
> Signed-off-by: Xi Wang <[email-masked]>
> Cc: Daniel Borkmann <[email-masked]>
> Cc: Heiko Carstens <[email-masked]>
> Cc: Will Drewry <[email-masked]>
> Cc: Eric Dumazet <[email-masked]>
> Cc: Russell King <[email-masked]>
> Cc: David Laight <[email-masked]>
> Cc: "David S. Miller" <[email-masked]>
> Cc: Andrew Morton <[email-masked]>
> Cc: Nicolas Schichan <[email-masked]>
> ---
>   arch/arm/net/bpf_jit_32.c | 14 ++++++++++++++
>   1 file changed, 14 insertions(+)
>
> diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
> index 073b085..9bfce464 100644
> --- a/arch/arm/net/bpf_jit_32.c
> +++ b/arch/arm/net/bpf_jit_32.c
> @@ -19,6 +19,7 @@
>   #include <linux/if_vlan.h>
>   #include <asm/cacheflush.h>
>   #include <asm/hwcap.h>
> +#include <asm/syscall.h>
>
>   #include "bpf_jit_32.h"
>
> @@ -845,6 +846,19 @@ b_epilogue:
>   			off = offsetof(struct sk_buff, queue_mapping);
>   			emit(ARM_LDRH_I(r_A, r_skb, off), ctx);
>   			break;
> +#ifdef CONFIG_SECCOMP_FILTER
> +		case BPF_S_ANC_SECCOMP_LD_W:
> +			if (k == offsetof(struct seccomp_data, arch)) {
> +				emit_mov_i(r_A, AUDIT_ARCH_ARM, ctx);
> +				break;
> +			}

Not an expert in ARM, but ...

Arent't you doing here a similar thing in terms of getting arch as Eric
criticized (Nicolas' implementation does not use that part btw.)? Also,
even if it would be possible here, now your 2 JIT implementations differ
in behaviour. I think this is unintended.

Besides all that, I think I also pointed you to a patch that already made
it in for ARM, not sure why you keep posting the ARM JIT implementation?

> +			ctx->seen |= SEEN_CALL;
> +			emit_mov_i(ARM_R3, (u32)seccomp_bpf_load, ctx);
> +			emit_mov_i(ARM_R0, k, ctx);
> +			emit_blx_r(ARM_R3, ctx);
> +			emit(ARM_MOV_R(r_A, ARM_R0), ctx);
> +			break;
> +#endif
>   		default:
>   			return -1;
>   		}
>