From 2d419c44658f75e7655794341a95c0687830f3df Mon Sep 17 00:00:00 2001 From: Menglong Dong Date: Sat, 24 Jan 2026 14:19:56 +0800 Subject: bpf: add fsession support The fsession is something that similar to kprobe session. It allow to attach a single BPF program to both the entry and the exit of the target functions. Introduce the struct bpf_fsession_link, which allows to add the link to both the fentry and fexit progs_hlist of the trampoline. Signed-off-by: Menglong Dong Co-developed-by: Leon Hwang Signed-off-by: Leon Hwang Link: https://lore.kernel.org/r/20260124062008.8657-2-dongml2@chinatelecom.cn Signed-off-by: Alexei Starovoitov --- include/linux/bpf.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) (limited to 'include/linux') diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 5936f8e2996f..41228b0add52 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1309,6 +1309,7 @@ enum bpf_tramp_prog_type { BPF_TRAMP_MODIFY_RETURN, BPF_TRAMP_MAX, BPF_TRAMP_REPLACE, /* more than MAX */ + BPF_TRAMP_FSESSION, }; struct bpf_tramp_image { @@ -1875,6 +1876,11 @@ struct bpf_tracing_link { struct bpf_prog *tgt_prog; }; +struct bpf_fsession_link { + struct bpf_tracing_link link; + struct bpf_tramp_link fexit; +}; + struct bpf_raw_tp_link { struct bpf_link link; struct bpf_raw_event_map *btp; @@ -2169,6 +2175,19 @@ static inline void bpf_struct_ops_desc_release(struct bpf_struct_ops_desc *st_op #endif +static inline int bpf_fsession_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->expected_attach_type == BPF_TRACE_FSESSION) + cnt++; + } + + return cnt; +} + int bpf_prog_ctx_arg_info_init(struct bpf_prog *prog, const struct bpf_ctx_arg_aux *info, u32 cnt); -- cgit v1.2.3 From 27d89baa6da8e5e546585c53a959176d1302d46e Mon Sep 17 00:00:00 2001 From: Menglong Dong Date: Sat, 24 Jan 2026 14:19:59 +0800 Subject: bpf: support fsession for bpf_session_is_return If fsession exists, we will use the bit (1 << BPF_TRAMP_IS_RETURN_SHIFT) in ((u64 *)ctx)[-1] to store the "is_return" flag. The logic of bpf_session_is_return() for fsession is implemented in the verifier by inline following code: bool bpf_session_is_return(void *ctx) { return (((u64 *)ctx)[-1] >> BPF_TRAMP_IS_RETURN_SHIFT) & 1; } Signed-off-by: Menglong Dong Co-developed-by: Leon Hwang Signed-off-by: Leon Hwang Link: https://lore.kernel.org/r/20260124062008.8657-5-dongml2@chinatelecom.cn Signed-off-by: Alexei Starovoitov --- include/linux/bpf.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/linux') diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 41228b0add52..29eecd79352e 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1229,6 +1229,8 @@ enum { #endif }; +#define BPF_TRAMP_IS_RETURN_SHIFT 63 + struct bpf_tramp_links { struct bpf_tramp_link *links[BPF_MAX_TRAMP_LINKS]; int nr_links; -- cgit v1.2.3 From eeee4239dbb155a98f8ba737324ac081acde8417 Mon Sep 17 00:00:00 2001 From: Menglong Dong Date: Sat, 24 Jan 2026 14:20:00 +0800 Subject: bpf: support fsession for bpf_session_cookie Implement session cookie for fsession. The session cookies will be stored in the stack, and the layout of 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 The offset of the cookie for the current bpf program, which is in 8-byte units, is stored in the "(((u64 *)ctx)[-1] >> BPF_TRAMP_COOKIE_INDEX_SHIFT) & 0xFF". Therefore, we can get the session cookie with ((u64 *)ctx)[-offset]. Implement and inline the bpf_session_cookie() for the fsession in the verifier. Signed-off-by: Menglong Dong Link: https://lore.kernel.org/r/20260124062008.8657-6-dongml2@chinatelecom.cn Signed-off-by: Alexei Starovoitov --- include/linux/bpf.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'include/linux') diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 29eecd79352e..4427c6e98331 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1229,6 +1229,7 @@ enum { #endif }; +#define BPF_TRAMP_COOKIE_INDEX_SHIFT 8 #define BPF_TRAMP_IS_RETURN_SHIFT 63 struct bpf_tramp_links { @@ -1782,6 +1783,7 @@ 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 */ @@ -2190,6 +2192,19 @@ 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); -- cgit v1.2.3