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Wed, 17 Dec 2025 01:55:20 -0800 (PST) From: Menglong Dong X-Google-Original-From: Menglong Dong To: ast@kernel.org, andrii@kernel.org Cc: davem@davemloft.net, dsahern@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH bpf-next v4 4/9] bpf: add the kfunc bpf_fsession_cookie Date: Wed, 17 Dec 2025 17:54:40 +0800 Message-ID: <20251217095445.218428-5-dongml2@chinatelecom.cn> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251217095445.218428-1-dongml2@chinatelecom.cn> References: <20251217095445.218428-1-dongml2@chinatelecom.cn> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Implement session cookie for fsession. In order to limit the stack usage, we make 4 as the maximum of the cookie count. The offset of the current cookie is stored in the "(ctx[-1] >> BPF_TRAMP_M_COOKIE) & 0xFF". Therefore, we can get the session cookie with ctx[-offset]. The stack will look like this: return value -> 8 bytes argN -> 8 bytes ... arg1 -> 8 bytes nr_args -> 8 bytes ip(optional) -> 8 bytes cookie2 -> 8 bytes cookie1 -> 8 bytes Inline the bpf_fsession_cookie() in the verifer too. Signed-off-by: Menglong Dong --- v4: - limit the maximum of the cookie count to 4 - store the session cookies before nr_regs in stack --- include/linux/bpf.h | 16 ++++++++++++++++ kernel/bpf/trampoline.c | 14 +++++++++++++- kernel/bpf/verifier.c | 20 ++++++++++++++++++-- kernel/trace/bpf_trace.c | 9 +++++++++ 4 files changed, 56 insertions(+), 3 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index d165ace5cc9b..0f35c6ab538c 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1215,6 +1215,7 @@ enum { #define BPF_TRAMP_M_NR_ARGS 0 #define BPF_TRAMP_M_IS_RETURN 8 +#define BPF_TRAMP_M_COOKIE 9 struct bpf_tramp_links { struct bpf_tramp_link *links[BPF_MAX_TRAMP_LINKS]; @@ -1318,6 +1319,7 @@ struct bpf_trampoline { struct mutex mutex; refcount_t refcnt; u32 flags; + int cookie_cnt; u64 key; struct { struct btf_func_model model; @@ -1762,6 +1764,7 @@ struct bpf_prog { enforce_expected_attach_type:1, /* Enforce expected_attach_type checking at attach time */ call_get_stack:1, /* Do we call bpf_get_stack() or bpf_get_stackid() */ call_get_func_ip:1, /* Do we call get_func_ip() */ + call_session_cookie:1, /* Do we call bpf_fsession_cookie() */ tstamp_type_access:1, /* Accessed __sk_buff->tstamp_type */ sleepable:1; /* BPF program is sleepable */ enum bpf_prog_type type; /* Type of BPF program */ @@ -2137,6 +2140,19 @@ static inline int bpf_fsession_cnt(struct bpf_tramp_links *links) return cnt; } +static inline int bpf_fsession_cookie_cnt(struct bpf_tramp_links *links) +{ + struct bpf_tramp_links fentries = links[BPF_TRAMP_FENTRY]; + int cnt = 0; + + for (int i = 0; i < links[BPF_TRAMP_FENTRY].nr_links; i++) { + if (fentries.links[i]->link.prog->call_session_cookie) + cnt++; + } + + return cnt; +} + int bpf_prog_ctx_arg_info_init(struct bpf_prog *prog, const struct bpf_ctx_arg_aux *info, u32 cnt); diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index 3b9fc99e1e89..68f3d73a94a9 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -592,6 +592,8 @@ static int bpf_freplace_check_tgt_prog(struct bpf_prog *tgt_prog) return 0; } +#define BPF_TRAMP_MAX_COOKIES 4 + static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr, struct bpf_prog *tgt_prog) @@ -599,7 +601,7 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, enum bpf_tramp_prog_type kind, okind; struct bpf_tramp_link *link_existing; struct bpf_fsession_link *fslink; - int err = 0; + int err = 0, cookie_cnt; int cnt = 0, i; okind = kind = bpf_attach_type_to_tramp(link->link.prog); @@ -640,6 +642,12 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, /* prog already linked */ return -EBUSY; } + cookie_cnt = tr->cookie_cnt; + if (link->link.prog->call_session_cookie) { + if (cookie_cnt >= BPF_TRAMP_MAX_COOKIES) + return -E2BIG; + cookie_cnt++; + } hlist_add_head(&link->tramp_hlist, &tr->progs_hlist[kind]); tr->progs_cnt[kind]++; @@ -657,6 +665,8 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, } hlist_del_init(&link->tramp_hlist); tr->progs_cnt[kind]--; + } else { + tr->cookie_cnt = cookie_cnt; } return err; } @@ -696,6 +706,8 @@ static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, hlist_del_init(&fslink->fexit.tramp_hlist); tr->progs_cnt[BPF_TRAMP_FEXIT]--; kind = BPF_TRAMP_FENTRY; + if (link->link.prog->call_session_cookie) + tr->cookie_cnt--; } hlist_del_init(&link->tramp_hlist); tr->progs_cnt[kind]--; diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b0dcd715150f..da8335cf7c46 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -12381,6 +12381,7 @@ enum special_kfunc_type { KF_bpf_task_work_schedule_signal_impl, KF_bpf_task_work_schedule_resume_impl, KF_bpf_fsession_is_return, + KF_bpf_fsession_cookie, }; BTF_ID_LIST(special_kfunc_list) @@ -12456,6 +12457,7 @@ BTF_ID(func, __bpf_trap) BTF_ID(func, bpf_task_work_schedule_signal_impl) BTF_ID(func, bpf_task_work_schedule_resume_impl) BTF_ID(func, bpf_fsession_is_return) +BTF_ID(func, bpf_fsession_cookie) static bool is_task_work_add_kfunc(u32 func_id) { @@ -12511,7 +12513,8 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env, bool arg_mem_size = false; if (meta->func_id == special_kfunc_list[KF_bpf_cast_to_kern_ctx] || - meta->func_id == special_kfunc_list[KF_bpf_fsession_is_return]) + meta->func_id == special_kfunc_list[KF_bpf_fsession_is_return] || + meta->func_id == special_kfunc_list[KF_bpf_fsession_cookie]) return KF_ARG_PTR_TO_CTX; /* In this function, we verify the kfunc's BTF as per the argument type, @@ -14009,7 +14012,8 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn, } } - if (meta.func_id == special_kfunc_list[KF_bpf_session_cookie]) { + if (meta.func_id == special_kfunc_list[KF_bpf_session_cookie] || + meta.func_id == special_kfunc_list[KF_bpf_fsession_cookie]) { meta.r0_size = sizeof(u64); meta.r0_rdonly = false; } @@ -14293,6 +14297,9 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn, return err; } + if (meta.func_id == special_kfunc_list[KF_bpf_fsession_cookie]) + env->prog->call_session_cookie = true; + return 0; } @@ -22565,6 +22572,15 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn, insn_buf[1] = BPF_ALU64_IMM(BPF_RSH, BPF_REG_0, BPF_TRAMP_M_IS_RETURN); insn_buf[2] = BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 1); *cnt = 3; + } else if (desc->func_id == special_kfunc_list[KF_bpf_fsession_cookie]) { + /* Load nr_args from ctx - 8 */ + insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8); + insn_buf[1] = BPF_ALU64_IMM(BPF_RSH, BPF_REG_0, BPF_TRAMP_M_COOKIE); + insn_buf[2] = BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xFF); + insn_buf[3] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_0, 3); + insn_buf[4] = BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1); + insn_buf[5] = BPF_ALU64_IMM(BPF_NEG, BPF_REG_0, 0); + *cnt = 6; } if (env->insn_aux_data[insn_idx].arg_prog) { diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 0857d77eb34c..ae7866d8ea62 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -3364,10 +3364,19 @@ __bpf_kfunc bool bpf_fsession_is_return(void *ctx) return !!(((u64 *)ctx)[-1] & (1 << BPF_TRAMP_M_IS_RETURN)); } +__bpf_kfunc u64 *bpf_fsession_cookie(void *ctx) +{ + /* This helper call is inlined by verifier. */ + u64 off = (((u64 *)ctx)[-1] >> BPF_TRAMP_M_COOKIE) & 0xFF; + + return &((u64 *)ctx)[-off]; +} + __bpf_kfunc_end_defs(); BTF_KFUNCS_START(tracing_kfunc_set_ids) BTF_ID_FLAGS(func, bpf_fsession_is_return, KF_FASTCALL) +BTF_ID_FLAGS(func, bpf_fsession_cookie, KF_FASTCALL) BTF_KFUNCS_END(tracing_kfunc_set_ids) static int bpf_tracing_filter(const struct bpf_prog *prog, u32 kfunc_id) -- 2.52.0