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selftests/bpf: update tcp_custom_syncookie to use scalar packet offset

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This commit updates tcp_custom_syncookie.c:tcp_parse_option() to use
explicit packet offset (ctx->off) for packet access instead of ever
moving pointer (ctx->ptr), this reduces verification complexity:
- the tcp_parse_option() is passed as a callback to bpf_loop();
- suppose a checkpoint is created each time at function entry;
- the ctx->ptr is tracked by verifier as PTR_TO_PACKET;
- the ctx->ptr is incremented in tcp_parse_option(),
  thus umax_value field tracked for it is incremented as well;
- on each next iteration of tcp_parse_option()
  checkpoint from a previous iteration can't be reused
  for state pruning, because PTR_TO_PACKET registers are
  considered equivalent only if old->umax_value >= cur->umax_value;
- on the other hand, the ctx->off is a SCALAR,
  subject to widen_imprecise_scalars();
- it's exact bounds are eventually forgotten and it is tracked as
  unknown scalar at entry to tcp_parse_option();
- hence checkpoints created at the start of the function eventually
  converge.

The change is similar to one applied in [0] to xdp_synproxy_kern.c.

Comparing before and after with veristat yields following results:

File                             Insns (A)  Insns (B)  Insns      (DIFF)
-------------------------------  ---------  ---------  -----------------
test_tcp_custom_syncookie.bpf.o     466657      12423  -454234 (-97.34%)

[0] commit 977bc146d4 ("selftests/bpf: track tcp payload offset as scalar in xdp_synproxy")

Acked-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240222150300.14909-2-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Eduard Zingerman 2024-02-22 17:03:00 +02:00 committed by Alexei Starovoitov
parent a3c70a3cf1
commit b546b57526
1 changed files with 52 additions and 29 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

81
tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
View File

@ -10,6 +10,8 @@
#include "test_siphash.h"
#include "test_tcp_custom_syncookie.h"
#define MAX_PACKET_OFF 0xffff
/* Hash is calculated for each client and split into ISN and TS.
*
* MSB LSB
@ -52,16 +54,15 @@ static siphash_key_t test_key_siphash = {
struct tcp_syncookie {
struct __sk_buff *skb;
void *data;
void *data_end;
struct ethhdr *eth;
struct iphdr *ipv4;
struct ipv6hdr *ipv6;
struct tcphdr *tcp;
union {
char *ptr;
__be32 *ptr32;
};
__be32 *ptr32;
struct bpf_tcp_req_attrs attrs;
u32 off;
u32 cookie;
u64 first;
};
@ -70,6 +71,7 @@ bool handled_syn, handled_ack;
static int tcp_load_headers(struct tcp_syncookie *ctx)
{
ctx->data = (void *)(long)ctx->skb->data;
ctx->data_end = (void *)(long)ctx->skb->data_end;
ctx->eth = (struct ethhdr *)(long)ctx->skb->data;
@ -134,6 +136,7 @@ static int tcp_reload_headers(struct tcp_syncookie *ctx)
if (bpf_skb_change_tail(ctx->skb, data_len + 60 - ctx->tcp->doff * 4, 0))
goto err;
ctx->data = (void *)(long)ctx->skb->data;
ctx->data_end = (void *)(long)ctx->skb->data_end;
ctx->eth = (struct ethhdr *)(long)ctx->skb->data;
if (ctx->ipv4) {
@ -195,47 +198,68 @@ err:
return -1;
}
static __always_inline void *next(struct tcp_syncookie *ctx, __u32 sz)
{
__u64 off = ctx->off;
__u8 *data;
/* Verifier forbids access to packet when offset exceeds MAX_PACKET_OFF */
if (off > MAX_PACKET_OFF - sz)
return NULL;
data = ctx->data + off;
barrier_var(data);
if (data + sz >= ctx->data_end)
return NULL;
ctx->off += sz;
return data;
}
static int tcp_parse_option(__u32 index, struct tcp_syncookie *ctx)
{
char opcode, opsize;
__u8 *opcode, *opsize, *wscale;
__u32 *tsval, *tsecr;
__u16 *mss;
__u32 off;
if (ctx->ptr + 1 > ctx->data_end)
off = ctx->off;
opcode = next(ctx, 1);
if (!opcode)
goto stop;
opcode = *ctx->ptr++;
if (opcode == TCPOPT_EOL)
if (*opcode == TCPOPT_EOL)
goto stop;
if (opcode == TCPOPT_NOP)
if (*opcode == TCPOPT_NOP)
goto next;
if (ctx->ptr + 1 > ctx->data_end)
opsize = next(ctx, 1);
if (!opsize)
goto stop;
opsize = *ctx->ptr++;
if (opsize < 2)
if (*opsize < 2)
goto stop;
switch (opcode) {
switch (*opcode) {
case TCPOPT_MSS:
if (opsize == TCPOLEN_MSS && ctx->tcp->syn &&
ctx->ptr + (TCPOLEN_MSS - 2) < ctx->data_end)
ctx->attrs.mss = get_unaligned_be16(ctx->ptr);
mss = next(ctx, 2);
if (*opsize == TCPOLEN_MSS && ctx->tcp->syn && mss)
ctx->attrs.mss = get_unaligned_be16(mss);
break;
case TCPOPT_WINDOW:
if (opsize == TCPOLEN_WINDOW && ctx->tcp->syn &&
ctx->ptr + (TCPOLEN_WINDOW - 2) < ctx->data_end) {
wscale = next(ctx, 1);
if (*opsize == TCPOLEN_WINDOW && ctx->tcp->syn && wscale) {
ctx->attrs.wscale_ok = 1;
ctx->attrs.snd_wscale = *ctx->ptr;
ctx->attrs.snd_wscale = *wscale;
}
break;
case TCPOPT_TIMESTAMP:
if (opsize == TCPOLEN_TIMESTAMP &&
ctx->ptr + (TCPOLEN_TIMESTAMP - 2) < ctx->data_end) {
ctx->attrs.rcv_tsval = get_unaligned_be32(ctx->ptr);
ctx->attrs.rcv_tsecr = get_unaligned_be32(ctx->ptr + 4);
tsval = next(ctx, 4);
tsecr = next(ctx, 4);
if (*opsize == TCPOLEN_TIMESTAMP && tsval && tsecr) {
ctx->attrs.rcv_tsval = get_unaligned_be32(tsval);
ctx->attrs.rcv_tsecr = get_unaligned_be32(tsecr);
if (ctx->tcp->syn && ctx->attrs.rcv_tsecr)
ctx->attrs.tstamp_ok = 0;
@ -244,13 +268,12 @@ static int tcp_parse_option(__u32 index, struct tcp_syncookie *ctx)
}
break;
case TCPOPT_SACK_PERM:
if (opsize == TCPOLEN_SACK_PERM && ctx->tcp->syn &&
ctx->ptr + (TCPOLEN_SACK_PERM - 2) < ctx->data_end)
if (*opsize == TCPOLEN_SACK_PERM && ctx->tcp->syn)
ctx->attrs.sack_ok = 1;
break;
}
ctx->ptr += opsize - 2;
ctx->off = off + *opsize;
next:
return 0;
stop:
@ -259,7 +282,7 @@ stop:
static void tcp_parse_options(struct tcp_syncookie *ctx)
{
ctx->ptr = (char *)(ctx->tcp + 1);
ctx->off = (__u8 *)(ctx->tcp + 1) - (__u8 *)ctx->data,
bpf_loop(40, tcp_parse_option, ctx, 0);
}