Commit eeee4239 authored by Menglong Dong's avatar Menglong Dong Committed by Alexei Starovoitov
Browse files

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: default avatarMenglong Dong <dongml2@chinatelecom.cn>
Link: https://lore.kernel.org/r/20260124062008.8657-6-dongml2@chinatelecom.cn


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 27d89baa

include/linux/bpf.h

+15 −0
Original line number Diff line number Diff line
@@ -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);

kernel/bpf/verifier.c

+20 −0
Original line number Diff line number Diff line
@@ -14406,6 +14406,9 @@ 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;









}
















@@ -23024,6 +23027,23 @@ 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_IS_RETURN_SHIFT);









		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) {









		/*









		 * inline bpf_session_cookie() for fsession:









		 *   __u64 *bpf_session_cookie(void *ctx)









		 *   {









		 *       u64 off = (((u64 *)ctx)[-1] >> BPF_TRAMP_COOKIE_INDEX_SHIFT) & 0xFF;









		 *       return &((u64 *)ctx)[-off];









		 *   }









		 */









		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_COOKIE_INDEX_SHIFT);









		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) {