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tc: bpf: add checksum helpers 

Commit 608cd71a9c ("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: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
wifi-calibration
Alexei Starovoitov 2015-04-01 17:12:13 -07:00 committed by David S. Miller
parent 5888b93b75
commit 91bc4822c3
5 changed files with 220 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
include/uapi/linux/bpf.h
View File

@ -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,
};

108
net/core/filter.c
View File

@ -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))
@ -1202,7 +1204,8 @@ static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
if (unlikely(!ptr))
return -EFAULT;
skb_postpull_rcsum(skb, ptr, len);
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);
}

1
samples/bpf/Makefile
View File

@ -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

7
samples/bpf/bpf_helpers.h
View File

@ -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

71
samples/bpf/tcbpf1_kern.c 100644
View File

@ -0,0 +1,71 @@
#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";