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Wed, 07 Jan 2026 18:25:57 -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 v8 05/11] bpf: support fsession for bpf_session_cookie Date: Thu, 8 Jan 2026 10:24:44 +0800 Message-ID: <20260108022450.88086-6-dongml2@chinatelecom.cn> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260108022450.88086-1-dongml2@chinatelecom.cn> References: <20260108022450.88086-1-dongml2@chinatelecom.cn> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 95248b0d28ab..699ad06e2465 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1231,6 +1231,7 @@ enum { =20 #define BPF_TRAMP_M_NR_ARGS 0 #define BPF_TRAMP_M_IS_RETURN 8 +#define BPF_TRAMP_M_COOKIE 9 =20 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 checki= ng 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; } =20 +static inline int bpf_fsession_cookie_cnt(struct bpf_tramp_links *links) +{ + struct bpf_tramp_links fentries =3D links[BPF_TRAMP_FENTRY]; + int cnt =3D 0; + + for (int i =3D 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); =20 @@ -3978,5 +3993,6 @@ static inline int bpf_map_check_op_flags(struct bpf_m= ap *map, u64 flags, u64 all } =20 bool bpf_fsession_is_return(void *ctx); +u64 *bpf_fsession_cookie(void *ctx); =20 #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; } =20 +#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 =3D 0; + int err =3D 0, cookie_cnt =3D 0; int cnt =3D 0, i; =20 kind =3D bpf_attach_type_to_tramp(link->link.prog); @@ -637,11 +639,18 @@ static int __bpf_trampoline_link_prog(struct bpf_tram= p_link *link, /* prog already linked */ return -EBUSY; hlist_for_each_entry(link_exiting, prog_list, tramp_hlist) { - if (link_exiting->link.prog !=3D link->link.prog) + if (link_exiting->link.prog !=3D link->link.prog) { + if (kind =3D=3D 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 >=3D BPF_TRAMP_MAX_COOKIES) + return -E2BIG; =20 hlist_add_head(&link->tramp_hlist, prog_list); if (kind =3D=3D 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 =3D false; =20 if (meta->func_id =3D=3D special_kfunc_list[KF_bpf_cast_to_kern_ctx] || - meta->func_id =3D=3D special_kfunc_list[KF_bpf_session_is_return]) + meta->func_id =3D=3D special_kfunc_list[KF_bpf_session_is_return] || + meta->func_id =3D=3D special_kfunc_list[KF_bpf_session_cookie]) return KF_ARG_PTR_TO_CTX; =20 if (argno + 1 < nargs && @@ -14294,6 +14295,9 @@ static int check_kfunc_call(struct bpf_verifier_env= *env, struct bpf_insn *insn, return err; } =20 + if (meta.func_id =3D=3D special_kfunc_list[KF_bpf_session_cookie]) + env->prog->call_session_cookie =3D true; + return 0; } =20 @@ -22446,6 +22450,9 @@ static int specialize_kfunc(struct bpf_verifier_env= *env, struct bpf_kfunc_desc } else if (func_id =3D=3D special_kfunc_list[KF_bpf_session_is_return]) { if (prog->expected_attach_type =3D=3D BPF_TRACE_FSESSION) addr =3D (unsigned long)bpf_fsession_is_return; + } else if (func_id =3D=3D special_kfunc_list[KF_bpf_session_cookie]) { + if (prog->expected_attach_type =3D=3D BPF_TRACE_FSESSION) + addr =3D (unsigned long)bpf_fsession_cookie; } desc->addr =3D addr; return 0; @@ -22571,6 +22578,16 @@ static int fixup_kfunc_call(struct bpf_verifier_en= v *env, struct bpf_insn *insn, insn_buf[1] =3D BPF_ALU64_IMM(BPF_RSH, BPF_REG_0, BPF_TRAMP_M_IS_RETURN); insn_buf[2] =3D BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 1); *cnt =3D 3; + } else if (desc->func_id =3D=3D special_kfunc_list[KF_bpf_session_cookie]= && + env->prog->expected_attach_type =3D=3D BPF_TRACE_FSESSION) { + /* Load nr_args from ctx - 8 */ + insn_buf[0] =3D BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8); + insn_buf[1] =3D BPF_ALU64_IMM(BPF_RSH, BPF_REG_0, BPF_TRAMP_M_COOKIE); + insn_buf[2] =3D BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xFF); + insn_buf[3] =3D BPF_ALU64_IMM(BPF_LSH, BPF_REG_0, 3); + insn_buf[4] =3D BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1); + insn_buf[5] =3D BPF_ALU64_IMM(BPF_NEG, BPF_REG_0, 0); + *cnt =3D 6; } =20 if (env->insn_aux_data[insn_idx].arg_prog) { diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 056f30844de2..665f10197fd7 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)); } =20 +u64 *bpf_fsession_cookie(void *ctx) +{ + /* This helper call is inlined by verifier. */ + u64 off =3D (((u64 *)ctx)[-1] >> BPF_TRAMP_M_COOKIE) & 0xFF; + + return &((u64 *)ctx)[-off]; +} + __bpf_kfunc_start_defs(); =20 __bpf_kfunc bool bpf_session_is_return(void *ctx) --=20 2.52.0