Commit 91bc4822 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by David S. Miller
Browse files

tc: bpf: add checksum helpers 



Commit 608cd71a ("tc: bpf: generalize pedit action") has added the
possibility to mangle packet data to BPF programs in the tc pipeline.
This patch adds two helpers bpf_l3_csum_replace() and bpf_l4_csum_replace()
for fixing up the protocol checksums after the packet mangling.

It also adds 'flags' argument to bpf_skb_store_bytes() helper to avoid
unnecessary checksum recomputations when BPF programs adjusting l3/l4
checksums and documents all three helpers in uapi header.

Moreover, a sample program is added to show how BPF programs can make use
of the mangle and csum helpers.

Signed-off-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 5888b93b

include/uapi/linux/bpf.h

+37 −1
Original line number Diff line number Diff line
@@ -168,7 +168,43 @@ enum bpf_func_id { 
	BPF_FUNC_map_delete_elem, /* int map_delete_elem(&map, &key) */

	BPF_FUNC_get_prandom_u32, /* u32 prandom_u32(void) */

	BPF_FUNC_get_smp_processor_id, /* u32 raw_smp_processor_id(void) */

	BPF_FUNC_skb_store_bytes, /* int skb_store_bytes(skb, offset, from, len) */



	/**

	 * skb_store_bytes(skb, offset, from, len, flags) - store bytes into packet

	 * @skb: pointer to skb

	 * @offset: offset within packet from skb->data

	 * @from: pointer where to copy bytes from

	 * @len: number of bytes to store into packet

	 * @flags: bit 0 - if true, recompute skb->csum

	 *         other bits - reserved

	 * Return: 0 on success

	 */

	BPF_FUNC_skb_store_bytes,



	/**

	 * l3_csum_replace(skb, offset, from, to, flags) - recompute IP checksum

	 * @skb: pointer to skb

	 * @offset: offset within packet where IP checksum is located

	 * @from: old value of header field

	 * @to: new value of header field

	 * @flags: bits 0-3 - size of header field

	 *         other bits - reserved

	 * Return: 0 on success

	 */

	BPF_FUNC_l3_csum_replace,



	/**

	 * l4_csum_replace(skb, offset, from, to, flags) - recompute TCP/UDP checksum

	 * @skb: pointer to skb

	 * @offset: offset within packet where TCP/UDP checksum is located

	 * @from: old value of header field

	 * @to: new value of header field

	 * @flags: bits 0-3 - size of header field

	 *         bit 4 - is pseudo header

	 *         other bits - reserved

	 * Return: 0 on success

	 */

	BPF_FUNC_l4_csum_replace,

	__BPF_FUNC_MAX_ID,

};

net/core/filter.c

+104 −4
Original line number Diff line number Diff line
@@ -1175,7 +1175,9 @@ int sk_attach_bpf(u32 ufd, struct sock *sk) 
	return 0;

}



static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)

#define BPF_RECOMPUTE_CSUM(flags)	((flags) & 1)



static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 flags)

{

	struct sk_buff *skb = (struct sk_buff *) (long) r1;

	unsigned int offset = (unsigned int) r2;
@@ -1192,7 +1194,7 @@ static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5) 
	 *

	 * so check for invalid 'offset' and too large 'len'

	 */

	if (offset > 0xffff || len > sizeof(buf))

	if (unlikely(offset > 0xffff || len > sizeof(buf)))

		return -EFAULT;



	if (skb_cloned(skb) && !skb_clone_writable(skb, offset + len))
@@ -1202,6 +1204,7 @@ static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5) 
	if (unlikely(!ptr))

		return -EFAULT;



	if (BPF_RECOMPUTE_CSUM(flags))

		skb_postpull_rcsum(skb, ptr, len);



	memcpy(ptr, from, len);
@@ -1210,7 +1213,7 @@ static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5) 
		/* skb_store_bits cannot return -EFAULT here */

		skb_store_bits(skb, offset, ptr, len);



	if (skb->ip_summed == CHECKSUM_COMPLETE)

	if (BPF_RECOMPUTE_CSUM(flags) && skb->ip_summed == CHECKSUM_COMPLETE)

		skb->csum = csum_add(skb->csum, csum_partial(ptr, len, 0));

	return 0;

}
@@ -1223,6 +1226,99 @@ const struct bpf_func_proto bpf_skb_store_bytes_proto = { 
	.arg2_type	= ARG_ANYTHING,

	.arg3_type	= ARG_PTR_TO_STACK,

	.arg4_type	= ARG_CONST_STACK_SIZE,

	.arg5_type	= ARG_ANYTHING,

};



#define BPF_HEADER_FIELD_SIZE(flags)	((flags) & 0x0f)

#define BPF_IS_PSEUDO_HEADER(flags)	((flags) & 0x10)



static u64 bpf_l3_csum_replace(u64 r1, u64 offset, u64 from, u64 to, u64 flags)

{

	struct sk_buff *skb = (struct sk_buff *) (long) r1;

	__sum16 sum, *ptr;



	if (unlikely(offset > 0xffff))

		return -EFAULT;



	if (skb_cloned(skb) && !skb_clone_writable(skb, offset + sizeof(sum)))

		return -EFAULT;



	ptr = skb_header_pointer(skb, offset, sizeof(sum), &sum);

	if (unlikely(!ptr))

		return -EFAULT;



	switch (BPF_HEADER_FIELD_SIZE(flags)) {

	case 2:

		csum_replace2(ptr, from, to);

		break;

	case 4:

		csum_replace4(ptr, from, to);

		break;

	default:

		return -EINVAL;

	}



	if (ptr == &sum)

		/* skb_store_bits guaranteed to not return -EFAULT here */

		skb_store_bits(skb, offset, ptr, sizeof(sum));



	return 0;

}



const struct bpf_func_proto bpf_l3_csum_replace_proto = {

	.func		= bpf_l3_csum_replace,

	.gpl_only	= false,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_CTX,

	.arg2_type	= ARG_ANYTHING,

	.arg3_type	= ARG_ANYTHING,

	.arg4_type	= ARG_ANYTHING,

	.arg5_type	= ARG_ANYTHING,

};



static u64 bpf_l4_csum_replace(u64 r1, u64 offset, u64 from, u64 to, u64 flags)

{

	struct sk_buff *skb = (struct sk_buff *) (long) r1;

	u32 is_pseudo = BPF_IS_PSEUDO_HEADER(flags);

	__sum16 sum, *ptr;



	if (unlikely(offset > 0xffff))

		return -EFAULT;



	if (skb_cloned(skb) && !skb_clone_writable(skb, offset + sizeof(sum)))

		return -EFAULT;



	ptr = skb_header_pointer(skb, offset, sizeof(sum), &sum);

	if (unlikely(!ptr))

		return -EFAULT;



	switch (BPF_HEADER_FIELD_SIZE(flags)) {

	case 2:

		inet_proto_csum_replace2(ptr, skb, from, to, is_pseudo);

		break;

	case 4:

		inet_proto_csum_replace4(ptr, skb, from, to, is_pseudo);

		break;

	default:

		return -EINVAL;

	}



	if (ptr == &sum)

		/* skb_store_bits guaranteed to not return -EFAULT here */

		skb_store_bits(skb, offset, ptr, sizeof(sum));



	return 0;

}



const struct bpf_func_proto bpf_l4_csum_replace_proto = {

	.func		= bpf_l4_csum_replace,

	.gpl_only	= false,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_CTX,

	.arg2_type	= ARG_ANYTHING,

	.arg3_type	= ARG_ANYTHING,

	.arg4_type	= ARG_ANYTHING,

	.arg5_type	= ARG_ANYTHING,

};



static const struct bpf_func_proto *
@@ -1250,6 +1346,10 @@ tc_cls_act_func_proto(enum bpf_func_id func_id) 
	switch (func_id) {

	case BPF_FUNC_skb_store_bytes:

		return &bpf_skb_store_bytes_proto;

	case BPF_FUNC_l3_csum_replace:

		return &bpf_l3_csum_replace_proto;

	case BPF_FUNC_l4_csum_replace:

		return &bpf_l4_csum_replace_proto;

	default:

		return sk_filter_func_proto(func_id);

	}

samples/bpf/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ sockex2-objs := bpf_load.o libbpf.o sockex2_user.o 
always := $(hostprogs-y)

always += sockex1_kern.o

always += sockex2_kern.o

always += tcbpf1_kern.o



HOSTCFLAGS += -I$(objtree)/usr/include

samples/bpf/bpf_helpers.h

+7 −0
Original line number Diff line number Diff line
@@ -37,4 +37,11 @@ struct bpf_map_def { 
	unsigned int max_entries;

};



static int (*bpf_skb_store_bytes)(void *ctx, int off, void *from, int len, int flags) =

	(void *) BPF_FUNC_skb_store_bytes;

static int (*bpf_l3_csum_replace)(void *ctx, int off, int from, int to, int flags) =

	(void *) BPF_FUNC_l3_csum_replace;

static int (*bpf_l4_csum_replace)(void *ctx, int off, int from, int to, int flags) =

	(void *) BPF_FUNC_l4_csum_replace;



#endif

samples/bpf/tcbpf1_kern.c

0 → 100644
+71 −0
Original line number Diff line number Diff line 
#include <uapi/linux/bpf.h>

#include <uapi/linux/if_ether.h>

#include <uapi/linux/if_packet.h>

#include <uapi/linux/ip.h>

#include <uapi/linux/in.h>

#include <uapi/linux/tcp.h>

#include "bpf_helpers.h"



/* compiler workaround */

#define _htonl __builtin_bswap32



static inline void set_dst_mac(struct __sk_buff *skb, char *mac)

{

	bpf_skb_store_bytes(skb, 0, mac, ETH_ALEN, 1);

}



/* use 1 below for ingress qdisc and 0 for egress */

#if 0

#undef ETH_HLEN

#define ETH_HLEN 0

#endif



#define IP_CSUM_OFF (ETH_HLEN + offsetof(struct iphdr, check))

#define TOS_OFF (ETH_HLEN + offsetof(struct iphdr, tos))



static inline void set_ip_tos(struct __sk_buff *skb, __u8 new_tos)

{

	__u8 old_tos = load_byte(skb, TOS_OFF);



	bpf_l3_csum_replace(skb, IP_CSUM_OFF, htons(old_tos), htons(new_tos), 2);

	bpf_skb_store_bytes(skb, TOS_OFF, &new_tos, sizeof(new_tos), 0);

}



#define TCP_CSUM_OFF (ETH_HLEN + sizeof(struct iphdr) + offsetof(struct tcphdr, check))

#define IP_SRC_OFF (ETH_HLEN + offsetof(struct iphdr, saddr))



#define IS_PSEUDO 0x10



static inline void set_tcp_ip_src(struct __sk_buff *skb, __u32 new_ip)

{

	__u32 old_ip = _htonl(load_word(skb, IP_SRC_OFF));



	bpf_l4_csum_replace(skb, TCP_CSUM_OFF, old_ip, new_ip, IS_PSEUDO | sizeof(new_ip));

	bpf_l3_csum_replace(skb, IP_CSUM_OFF, old_ip, new_ip, sizeof(new_ip));

	bpf_skb_store_bytes(skb, IP_SRC_OFF, &new_ip, sizeof(new_ip), 0);

}



#define TCP_DPORT_OFF (ETH_HLEN + sizeof(struct iphdr) + offsetof(struct tcphdr, dest))

static inline void set_tcp_dest_port(struct __sk_buff *skb, __u16 new_port)

{

	__u16 old_port = htons(load_half(skb, TCP_DPORT_OFF));



	bpf_l4_csum_replace(skb, TCP_CSUM_OFF, old_port, new_port, sizeof(new_port));

	bpf_skb_store_bytes(skb, TCP_DPORT_OFF, &new_port, sizeof(new_port), 0);

}



SEC("classifier")

int bpf_prog1(struct __sk_buff *skb)

{

	__u8 proto = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol));

	long *value;



	if (proto == IPPROTO_TCP) {

		set_ip_tos(skb, 8);

		set_tcp_ip_src(skb, 0xA010101);

		set_tcp_dest_port(skb, 5001);

	}



	return 0;

}

char _license[] SEC("license") = "GPL";

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