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[176.36.0.241]) by smtp.gmail.com with ESMTPSA id rf20-20020a1709076a1400b00a3f2bf468b9sm1869059ejc.173.2024.02.22.07.03.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Feb 2024 07:03:28 -0800 (PST) From: Eduard Zingerman To: bpf@vger.kernel.org, ast@kernel.org Cc: andrii@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, kernel-team@fb.com, yonghong.song@linux.dev, kuniyu@amazon.com, Eduard Zingerman Subject: [PATCH bpf-next 1/1] selftests/bpf: update tcp_custom_syncookie to use scalar packet offset Date: Thu, 22 Feb 2024 17:03:00 +0200 Message-ID: <20240222150300.14909-2-eddyz87@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240222150300.14909-1-eddyz87@gmail.com> References: <20240222150300.14909-1-eddyz87@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: bpf@iogearbox.net 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 977bc146d4eb ("selftests/bpf: track tcp payload offset as scalar in xdp_synproxy") Acked-by: Yonghong Song Signed-off-by: Eduard Zingerman --- .../bpf/progs/test_tcp_custom_syncookie.c | 83 ++++++++++++------- 1 file changed, 53 insertions(+), 30 deletions(-) diff --git a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c index a5501b29979a..c8e4553648bf 100644 --- a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c +++ b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c @@ -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 @@ static int tcp_validate_header(struct tcp_syncookie *ctx) return -1; } -static int tcp_parse_option(__u32 index, struct tcp_syncookie *ctx) +static __always_inline void *next(struct tcp_syncookie *ctx, __u32 sz) { - char opcode, opsize; + __u64 off = ctx->off; + __u8 *data; - if (ctx->ptr + 1 > ctx->data_end) - goto stop; + /* 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; - opcode = *ctx->ptr++; + ctx->off += sz; + return data; +} - if (opcode == TCPOPT_EOL) +static int tcp_parse_option(__u32 index, struct tcp_syncookie *ctx) +{ + __u8 *opcode, *opsize, *wscale; + __u32 *tsval, *tsecr; + __u16 *mss; + __u32 off; + + off = ctx->off; + opcode = next(ctx, 1); + if (!opcode) goto stop; - if (opcode == TCPOPT_NOP) + if (*opcode == TCPOPT_EOL) + goto stop; + + 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 @@ static int tcp_parse_option(__u32 index, struct tcp_syncookie *ctx) 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); }