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Tue, 06 Jan 2026 22:44:58 -0800 (PST) From: Menglong Dong X-Google-Original-From: Menglong Dong To: ast@kernel.org, andrii@kernel.org Cc: 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, davem@davemloft.net, dsahern@kernel.org, tglx@linutronix.de, mingo@redhat.com, jiang.biao@linux.dev, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH bpf-next v7 05/11] bpf: support fsession for bpf_session_cookie Date: Wed, 7 Jan 2026 14:43:46 +0800 Message-ID: <20260107064352.291069-6-dongml2@chinatelecom.cn> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260107064352.291069-1-dongml2@chinatelecom.cn> References: <20260107064352.291069-1-dongml2@chinatelecom.cn> Precedence: bulk X-Mailing-List: netdev@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 verifier too. The calling to bpf_session_cookie() will be changed to bpf_fsession_cookie() in verifier for fsession. Signed-off-by: Menglong Dong --- v7: - reuse bpf_session_cookie() instead of introduce new kfunc v5: - remove "cookie_cnt" in struct bpf_trampoline 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 | 13 +++++++++++-- kernel/bpf/verifier.c | 19 ++++++++++++++++++- kernel/trace/bpf_trace.c | 8 ++++++++ 4 files changed, 53 insertions(+), 3 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index d996dd390681..31e03886c864 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1231,6 +1231,7 @@ 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]; @@ -1783,6 +1784,7 @@ 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_session_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 */ @@ -2191,6 +2193,19 @@ 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); @@ -3949,5 +3964,6 @@ static inline int bpf_map_check_op_flags(struct bpf_map *map, u64 flags, u64 all } bool bpf_fsession_is_return(void *ctx); +u64 *bpf_fsession_cookie(void *ctx); #endif /* _LINUX_BPF_H */ diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index 11e043049d68..29b4e00d860c 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) @@ -600,7 +602,7 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_tramp_link *link_exiting; struct bpf_fsession_link *fslink; struct hlist_head *prog_list; - int err = 0; + int err = 0, cookie_cnt = 0; int cnt = 0, i; kind = bpf_attach_type_to_tramp(link->link.prog); @@ -637,11 +639,18 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, /* prog already linked */ return -EBUSY; hlist_for_each_entry(link_exiting, prog_list, tramp_hlist) { - if (link_exiting->link.prog != link->link.prog) + if (link_exiting->link.prog != link->link.prog) { + if (kind == BPF_TRAMP_FSESSION && + link_exiting->link.prog->call_session_cookie) + cookie_cnt++; continue; + } /* prog already linked */ return -EBUSY; } + if (link->link.prog->call_session_cookie && + cookie_cnt >= BPF_TRAMP_MAX_COOKIES) + return -E2BIG; hlist_add_head(&link->tramp_hlist, prog_list); if (kind == BPF_TRAMP_FSESSION) { diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d3709edd0e51..210af94e3957 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -12508,7 +12508,8 @@ 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_session_is_return]) + meta->func_id == special_kfunc_list[KF_bpf_session_is_return] || + meta->func_id == special_kfunc_list[KF_bpf_session_cookie]) return KF_ARG_PTR_TO_CTX; if (argno + 1 < nargs && @@ -14294,6 +14295,9 @@ 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_session_cookie]) + env->prog->call_session_cookie = true; + return 0; } @@ -22446,6 +22450,9 @@ static int specialize_kfunc(struct bpf_verifier_env *env, struct bpf_kfunc_desc } else if (func_id == special_kfunc_list[KF_bpf_session_is_return]) { if (prog->expected_attach_type == BPF_TRACE_FSESSION) addr = (unsigned long)bpf_fsession_is_return; + } else if (func_id == special_kfunc_list[KF_bpf_session_cookie]) { + if (prog->expected_attach_type == BPF_TRACE_FSESSION) + addr = (unsigned long)bpf_fsession_cookie; } desc->addr = addr; return 0; @@ -22571,6 +22578,16 @@ 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_session_cookie] && + env->prog->expected_attach_type == BPF_TRACE_FSESSION) { + /* 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 9d3bf3bbe8f6..4960bb69cb30 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -3320,6 +3320,14 @@ bool bpf_fsession_is_return(void *ctx) return !!(((u64 *)ctx)[-1] & (1 << BPF_TRAMP_M_IS_RETURN)); } +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_start_defs(); __bpf_kfunc bool bpf_session_is_return(void *ctx) -- 2.52.0