From: Eric Dumazet Date: Mon, 1 Jun 2026 09:38:19 +0000 (+0000) Subject: tcp: change bpf_skops_hdr_opt_len() signature X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ceac8dbce6c30f1eda0534b7dea91bfb4d050145;p=thirdparty%2Flinux.git tcp: change bpf_skops_hdr_opt_len() signature Some compilers do not inline bpf_skops_hdr_opt_len() from tcp_established_options(), forcing an expensive stack canary when CONFIG_STACKPROTECTOR_STRONG=y. Change bpf_skops_hdr_opt_len() to return @remaining by value to remove this stack canary from TCP fast path. $ scripts/bloat-o-meter -t vmlinux.old vmlinux.new add/remove: 0/0 grow/shrink: 1/1 up/down: 10/-59 (-49) Function old new delta bpf_skops_hdr_opt_len 297 307 +10 tcp_established_options 574 515 -59 Total: Before=31456795, After=31456746, chg -0.00% Signed-off-by: Eric Dumazet Acked-by: Stanislav Fomichev Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20260601093819.469626-1-edumazet@google.com Signed-off-by: Jakub Kicinski --- diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index ef0c10cd31c7..1b0a066bb6a3 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -466,22 +466,22 @@ static int bpf_skops_write_hdr_opt_arg0(struct sk_buff *skb, } /* req, syn_skb and synack_type are used when writing synack */ -static void bpf_skops_hdr_opt_len(struct sock *sk, struct sk_buff *skb, - struct request_sock *req, - struct sk_buff *syn_skb, - enum tcp_synack_type synack_type, - struct tcp_out_options *opts, - unsigned int *remaining) +static u32 bpf_skops_hdr_opt_len(struct sock *sk, struct sk_buff *skb, + struct request_sock *req, + struct sk_buff *syn_skb, + enum tcp_synack_type synack_type, + struct tcp_out_options *opts, + u32 remaining) { struct bpf_sock_ops_kern sock_ops; int err; if (likely(!BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk), BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG)) || - !*remaining) - return; + !remaining) + return remaining; - /* *remaining has already been aligned to 4 bytes, so *remaining >= 4 */ + /* remaining has already been aligned to 4 bytes, so remaining >= 4 */ /* init sock_ops */ memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp)); @@ -513,21 +513,21 @@ static void bpf_skops_hdr_opt_len(struct sock *sk, struct sk_buff *skb, } sock_ops.args[0] = bpf_skops_write_hdr_opt_arg0(skb, synack_type); - sock_ops.remaining_opt_len = *remaining; + sock_ops.remaining_opt_len = remaining; /* tcp_current_mss() does not pass a skb */ if (skb) bpf_skops_init_skb(&sock_ops, skb, 0); err = BPF_CGROUP_RUN_PROG_SOCK_OPS_SK(&sock_ops, sk); - if (err || sock_ops.remaining_opt_len == *remaining) - return; + if (err || sock_ops.remaining_opt_len == remaining) + return remaining; - opts->bpf_opt_len = *remaining - sock_ops.remaining_opt_len; + opts->bpf_opt_len = remaining - sock_ops.remaining_opt_len; /* round up to 4 bytes */ opts->bpf_opt_len = (opts->bpf_opt_len + 3) & ~3; - *remaining -= opts->bpf_opt_len; + return remaining - opts->bpf_opt_len; } static void bpf_skops_write_hdr_opt(struct sock *sk, struct sk_buff *skb, @@ -575,13 +575,14 @@ static void bpf_skops_write_hdr_opt(struct sock *sk, struct sk_buff *skb, max_opt_len - nr_written); } #else -static void bpf_skops_hdr_opt_len(struct sock *sk, struct sk_buff *skb, - struct request_sock *req, - struct sk_buff *syn_skb, - enum tcp_synack_type synack_type, - struct tcp_out_options *opts, - unsigned int *remaining) +static u32 bpf_skops_hdr_opt_len(struct sock *sk, struct sk_buff *skb, + struct request_sock *req, + struct sk_buff *syn_skb, + enum tcp_synack_type synack_type, + struct tcp_out_options *opts, + u32 remaining) { + return remaining; } static void bpf_skops_write_hdr_opt(struct sock *sk, struct sk_buff *skb, @@ -1050,7 +1051,8 @@ static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb, remaining -= tcp_options_fit_accecn(opts, 0, remaining); } - bpf_skops_hdr_opt_len(sk, skb, NULL, NULL, 0, opts, &remaining); + remaining = bpf_skops_hdr_opt_len(sk, skb, NULL, NULL, 0, opts, + remaining); return MAX_TCP_OPTION_SPACE - remaining; } @@ -1137,8 +1139,8 @@ static unsigned int tcp_synack_options(const struct sock *sk, remaining -= tcp_options_fit_accecn(opts, 0, remaining); } - bpf_skops_hdr_opt_len((struct sock *)sk, skb, req, syn_skb, - synack_type, opts, &remaining); + remaining = bpf_skops_hdr_opt_len((struct sock *)sk, skb, req, syn_skb, + synack_type, opts, remaining); return MAX_TCP_OPTION_SPACE - remaining; } @@ -1227,7 +1229,8 @@ static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG))) { unsigned int remaining = MAX_TCP_OPTION_SPACE - size; - bpf_skops_hdr_opt_len(sk, skb, NULL, NULL, 0, opts, &remaining); + remaining = bpf_skops_hdr_opt_len(sk, skb, NULL, NULL, 0, opts, + remaining); size = MAX_TCP_OPTION_SPACE - remaining; }