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Commit 3b58908a authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

x86: bpf_jit_comp: add pkt_type support 



Supporting access to skb->pkt_type is a bit tricky if we want
to have a generic code, allowing pkt_type to be moved in struct sk_buff

pkt_type is a bit field, so compiler cannot really help us to find
its offset. Let's use a helper for this : It will throw a one time
message if pkt_type no longer starts at a byte boundary or is
no longer a 3bit field.

Reported-by: default avatarWillem de Bruijn <willemb@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Maciej Żenczykowski <maze@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 45acd3a0

arch/x86/net/bpf_jit_comp.c

+39 −1
Original line number Diff line number Diff line 
/* bpf_jit_comp.c : BPF JIT compiler

 *

 * Copyright (C) 2011 Eric Dumazet (eric.dumazet@gmail.com)

 * Copyright (C) 2011-2013 Eric Dumazet (eric.dumazet@gmail.com)

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License
@@ -124,6 +124,26 @@ static inline void bpf_flush_icache(void *start, void *end) 
#define CHOOSE_LOAD_FUNC(K, func) \

	((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset)



/* Helper to find the offset of pkt_type in sk_buff

 * We want to make sure its still a 3bit field starting at a byte boundary.

 */

#define PKT_TYPE_MAX 7

static int pkt_type_offset(void)

{

	struct sk_buff skb_probe = {

		.pkt_type = ~0,

	};

	char *ct = (char *)&skb_probe;

	unsigned int off;



	for (off = 0; off < sizeof(struct sk_buff); off++) {

		if (ct[off] == PKT_TYPE_MAX)

			return off;

	}

	pr_err_once("Please fix pkt_type_offset(), as pkt_type couldn't be found\n");

	return -1;

}



void bpf_jit_compile(struct sk_filter *fp)

{

	u8 temp[64];
@@ -216,6 +236,7 @@ void bpf_jit_compile(struct sk_filter *fp) 
		case BPF_S_ANC_VLAN_TAG:

		case BPF_S_ANC_VLAN_TAG_PRESENT:

		case BPF_S_ANC_QUEUE:

		case BPF_S_ANC_PKTTYPE:

		case BPF_S_LD_W_ABS:

		case BPF_S_LD_H_ABS:

		case BPF_S_LD_B_ABS:
@@ -536,6 +557,23 @@ void bpf_jit_compile(struct sk_filter *fp) 
					EMIT3(0x83, 0xe0, 0x01); /* and    $0x1,%eax */

				}

				break;

			case BPF_S_ANC_PKTTYPE:

			{

				int off = pkt_type_offset();



				if (off < 0)

					goto out;

				if (is_imm8(off)) {

					/* movzbl off8(%rdi),%eax */

					EMIT4(0x0f, 0xb6, 0x47, off);

				} else {

					/* movbl off32(%rdi),%eax */

					EMIT3(0x0f, 0xb6, 0x87);

					EMIT(off, 4);

				}

				EMIT3(0x83, 0xe0, PKT_TYPE_MAX); /* and    $0x7,%eax */

				break;

			}

			case BPF_S_LD_W_ABS:

				func = CHOOSE_LOAD_FUNC(K, sk_load_word);

common_load:			seen |= SEEN_DATAREF;