Merge branch 'bpf: Support calling kernel function'

Martin KaFai says:

====================

This series adds support to allow bpf program calling kernel function.

The use case included in this set is to allow bpf-tcp-cc to directly
call some tcp-cc helper functions (e.g. "tcp_cong_avoid_ai()").  Those
functions have already been used by some kernel tcp-cc implementations.

This set will also allow the bpf-tcp-cc program to directly call the
kernel tcp-cc implementation,  For example, a bpf_dctcp may only want to
implement its own dctcp_cwnd_event() and reuse other dctcp_*() directly
from the kernel tcp_dctcp.c instead of reimplementing (or
copy-and-pasting) them.

The tcp-cc kernel functions mentioned above will be white listed
for the struct_ops bpf-tcp-cc programs to use in a later patch.
The white listed functions are not bounded to a fixed ABI contract.
Those functions have already been used by the existing kernel tcp-cc.
If any of them has changed, both in-tree and out-of-tree kernel tcp-cc
implementations have to be changed.  The same goes for the struct_ops
bpf-tcp-cc programs which have to be adjusted accordingly.

Please see individual patch for details.

v2:
- Patch 2 in v1 is removed.  No need to support extern func in kernel.
  Changed libbpf to adjust the .ksyms datasec for extern func
  in patch 11. (Andrii)
- Name change: btf_check_func_arg_match() and btf_check_subprog_arg_match()
  in patch 2. (Andrii)
- Always set unreliable on any error in patch 2 since it does not
  matter. (Andrii)
- s/kern_func/kfunc/ and s/descriptor/desc/ in this set. (Andrii)
- Remove some unnecessary changes in disasm.h and disasm.c
  in patch 3.  In particular, no need to change the function
  signature in bpf_insn_revmap_call_t.  Also, removed the changes
  in print_bpf_insn().
- Fixed an issue in check_kfunc_call() when the calling kernel function
  returns a pointer in patch 3.  Added a selftest.
- Adjusted the verifier selftests due to the changes in the verifier log
  in patch 3.
- Fixed a comparison issue in kfunc_desc_cmp_by_imm() in patch 3. (Andrii)
- Name change: is_ldimm64_insn(),
  new helper: is_call_insn() in patch 10 (Andrii)
- Move btf_func_linkage() from btf.h to libbpf.c in patch 11. (Andrii)
- Fixed the linker error when CONFIG_BPF_SYSCALL is not defined.
  Moved the check_kfunc_call from filter.c to test_run.c in patch 14.
  (kernel test robot)
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

arch/x86/net/bpf_jit_comp.c

@@ -2346,3 +2346,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 					   tmp : orig_prog);
 	return prog;
 }
+
+bool bpf_jit_supports_kfunc_call(void)
+{
+	return true;
+}

arch/x86/net/bpf_jit_comp32.c

@@ -1390,6 +1390,19 @@ static inline void emit_push_r64(const u8 src[], u8 **pprog)
 	*pprog = prog;
 }
 
+static void emit_push_r32(const u8 src[], u8 **pprog)
+{
+	u8 *prog = *pprog;
+	int cnt = 0;
+
+	/* mov ecx,dword ptr [ebp+off] */
+	EMIT3(0x8B, add_2reg(0x40, IA32_EBP, IA32_ECX), STACK_VAR(src_lo));
+	/* push ecx */
+	EMIT1(0x51);
+
+	*pprog = prog;
+}
+
 static u8 get_cond_jmp_opcode(const u8 op, bool is_cmp_lo)
 {
 	u8 jmp_cond;
@@ -1459,6 +1472,174 @@ static u8 get_cond_jmp_opcode(const u8 op, bool is_cmp_lo)
 	return jmp_cond;
 }
 
+/* i386 kernel compiles with "-mregparm=3".  From gcc document:
+ *
+ * ==== snippet ====
+ * regparm (number)
+ *	On x86-32 targets, the regparm attribute causes the compiler
+ *	to pass arguments number one to (number) if they are of integral
+ *	type in registers EAX, EDX, and ECX instead of on the stack.
+ *	Functions that take a variable number of arguments continue
+ *	to be passed all of their arguments on the stack.
+ * ==== snippet ====
+ *
+ * The first three args of a function will be considered for
+ * putting into the 32bit register EAX, EDX, and ECX.
+ *
+ * Two 32bit registers are used to pass a 64bit arg.
+ *
+ * For example,
+ * void foo(u32 a, u32 b, u32 c, u32 d):
+ *	u32 a: EAX
+ *	u32 b: EDX
+ *	u32 c: ECX
+ *	u32 d: stack
+ *
+ * void foo(u64 a, u32 b, u32 c):
+ *	u64 a: EAX (lo32) EDX (hi32)
+ *	u32 b: ECX
+ *	u32 c: stack
+ *
+ * void foo(u32 a, u64 b, u32 c):
+ *	u32 a: EAX
+ *	u64 b: EDX (lo32) ECX (hi32)
+ *	u32 c: stack
+ *
+ * void foo(u32 a, u32 b, u64 c):
+ *	u32 a: EAX
+ *	u32 b: EDX
+ *	u64 c: stack
+ *
+ * The return value will be stored in the EAX (and EDX for 64bit value).
+ *
+ * For example,
+ * u32 foo(u32 a, u32 b, u32 c):
+ *	return value: EAX
+ *
+ * u64 foo(u32 a, u32 b, u32 c):
+ *	return value: EAX (lo32) EDX (hi32)
+ *
+ * Notes:
+ *	The verifier only accepts function having integer and pointers
+ *	as its args and return value, so it does not have
+ *	struct-by-value.
+ *
+ * emit_kfunc_call() finds out the btf_func_model by calling
+ * bpf_jit_find_kfunc_model().  A btf_func_model
+ * has the details about the number of args, size of each arg,
+ * and the size of the return value.
+ *
+ * It first decides how many args can be passed by EAX, EDX, and ECX.
+ * That will decide what args should be pushed to the stack:
+ * [first_stack_regno, last_stack_regno] are the bpf regnos
+ * that should be pushed to the stack.
+ *
+ * It will first push all args to the stack because the push
+ * will need to use ECX.  Then, it moves
+ * [BPF_REG_1, first_stack_regno) to EAX, EDX, and ECX.
+ *
+ * When emitting a call (0xE8), it needs to figure out
+ * the jmp_offset relative to the jit-insn address immediately
+ * following the call (0xE8) instruction.  At this point, it knows
+ * the end of the jit-insn address after completely translated the
+ * current (BPF_JMP | BPF_CALL) bpf-insn.  It is passed as "end_addr"
+ * to the emit_kfunc_call().  Thus, it can learn the "immediate-follow-call"
+ * address by figuring out how many jit-insn is generated between
+ * the call (0xE8) and the end_addr:
+ *	- 0-1 jit-insn (3 bytes each) to restore the esp pointer if there
+ *	  is arg pushed to the stack.
+ *	- 0-2 jit-insns (3 bytes each) to handle the return value.
+ */
+static int emit_kfunc_call(const struct bpf_prog *bpf_prog, u8 *end_addr,
+			   const struct bpf_insn *insn, u8 **pprog)
+{
+	const u8 arg_regs[] = { IA32_EAX, IA32_EDX, IA32_ECX };
+	int i, cnt = 0, first_stack_regno, last_stack_regno;
+	int free_arg_regs = ARRAY_SIZE(arg_regs);
+	const struct btf_func_model *fm;
+	int bytes_in_stack = 0;
+	const u8 *cur_arg_reg;
+	u8 *prog = *pprog;
+	s64 jmp_offset;
+
+	fm = bpf_jit_find_kfunc_model(bpf_prog, insn);
+	if (!fm)
+		return -EINVAL;
+
+	first_stack_regno = BPF_REG_1;
+	for (i = 0; i < fm->nr_args; i++) {
+		int regs_needed = fm->arg_size[i] > sizeof(u32) ? 2 : 1;
+
+		if (regs_needed > free_arg_regs)
+			break;
+
+		free_arg_regs -= regs_needed;
+		first_stack_regno++;
+	}
+
+	/* Push the args to the stack */
+	last_stack_regno = BPF_REG_0 + fm->nr_args;
+	for (i = last_stack_regno; i >= first_stack_regno; i--) {
+		if (fm->arg_size[i - 1] > sizeof(u32)) {
+			emit_push_r64(bpf2ia32[i], &prog);
+			bytes_in_stack += 8;
+		} else {
+			emit_push_r32(bpf2ia32[i], &prog);
+			bytes_in_stack += 4;
+		}
+	}
+
+	cur_arg_reg = &arg_regs[0];
+	for (i = BPF_REG_1; i < first_stack_regno; i++) {
+		/* mov e[adc]x,dword ptr [ebp+off] */
+		EMIT3(0x8B, add_2reg(0x40, IA32_EBP, *cur_arg_reg++),
+		      STACK_VAR(bpf2ia32[i][0]));
+		if (fm->arg_size[i - 1] > sizeof(u32))
+			/* mov e[adc]x,dword ptr [ebp+off] */
+			EMIT3(0x8B, add_2reg(0x40, IA32_EBP, *cur_arg_reg++),
+			      STACK_VAR(bpf2ia32[i][1]));
+	}
+
+	if (bytes_in_stack)
+		/* add esp,"bytes_in_stack" */
+		end_addr -= 3;
+
+	/* mov dword ptr [ebp+off],edx */
+	if (fm->ret_size > sizeof(u32))
+		end_addr -= 3;
+
+	/* mov dword ptr [ebp+off],eax */
+	if (fm->ret_size)
+		end_addr -= 3;
+
+	jmp_offset = (u8 *)__bpf_call_base + insn->imm - end_addr;
+	if (!is_simm32(jmp_offset)) {
+		pr_err("unsupported BPF kernel function jmp_offset:%lld\n",
+		       jmp_offset);
+		return -EINVAL;
+	}
+
+	EMIT1_off32(0xE8, jmp_offset);
+
+	if (fm->ret_size)
+		/* mov dword ptr [ebp+off],eax */
+		EMIT3(0x89, add_2reg(0x40, IA32_EBP, IA32_EAX),
+		      STACK_VAR(bpf2ia32[BPF_REG_0][0]));
+
+	if (fm->ret_size > sizeof(u32))
+		/* mov dword ptr [ebp+off],edx */
+		EMIT3(0x89, add_2reg(0x40, IA32_EBP, IA32_EDX),
+		      STACK_VAR(bpf2ia32[BPF_REG_0][1]));
+
+	if (bytes_in_stack)
+		/* add esp,"bytes_in_stack" */
+		EMIT3(0x83, add_1reg(0xC0, IA32_ESP), bytes_in_stack);
+
+	*pprog = prog;
+
+	return 0;
+}
+
 static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 		  int oldproglen, struct jit_context *ctx)
 {
@@ -1888,6 +2069,18 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			if (insn->src_reg == BPF_PSEUDO_CALL)
 				goto notyet;
 
+			if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {
+				int err;
+
+				err = emit_kfunc_call(bpf_prog,
+						      image + addrs[i],
+						      insn, &prog);
+
+				if (err)
+					return err;
+				break;
+			}
+
 			func = (u8 *) __bpf_call_base + imm32;
 			jmp_offset = func - (image + addrs[i]);
 
@@ -2393,3 +2586,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 					   tmp : orig_prog);
 	return prog;
 }
+
+bool bpf_jit_supports_kfunc_call(void)
+{
+	return true;
+}

include/linux/bpf.h

@@ -427,6 +427,7 @@ enum bpf_reg_type {
 	PTR_TO_PERCPU_BTF_ID,	 /* reg points to a percpu kernel variable */
 	PTR_TO_FUNC,		 /* reg points to a bpf program function */
 	PTR_TO_MAP_KEY,		 /* reg points to a map element key */
+	__BPF_REG_TYPE_MAX,
 };
 
 /* The information passed from prog-specific *_is_valid_access
@@ -480,6 +481,7 @@ struct bpf_verifier_ops {
 				 const struct btf_type *t, int off, int size,
 				 enum bpf_access_type atype,
 				 u32 *next_btf_id);
+	bool (*check_kfunc_call)(u32 kfunc_btf_id);
 };
 
 struct bpf_prog_offload_ops {
@@ -796,6 +798,8 @@ struct btf_mod_pair {
 	struct module *module;
 };
 
+struct bpf_kfunc_desc_tab;
+
 struct bpf_prog_aux {
 	atomic64_t refcnt;
 	u32 used_map_cnt;
@@ -832,6 +836,7 @@ struct bpf_prog_aux {
 	struct bpf_prog **func;
 	void *jit_data; /* JIT specific data. arch dependent */
 	struct bpf_jit_poke_descriptor *poke_tab;
+	struct bpf_kfunc_desc_tab *kfunc_tab;
 	u32 size_poke_tab;
 	struct bpf_ksym ksym;
 	const struct bpf_prog_ops *ops;
@@ -1527,6 +1532,7 @@ int bpf_prog_test_run_raw_tp(struct bpf_prog *prog,
 int bpf_prog_test_run_sk_lookup(struct bpf_prog *prog,
 				const union bpf_attr *kattr,
 				union bpf_attr __user *uattr);
+bool bpf_prog_test_check_kfunc_call(u32 kfunc_id);
 bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 		    const struct bpf_prog *prog,
 		    struct bpf_insn_access_aux *info);
@@ -1545,8 +1551,11 @@ int btf_distill_func_proto(struct bpf_verifier_log *log,
 			   struct btf_func_model *m);
 
 struct bpf_reg_state;
-int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
-			     struct bpf_reg_state *regs);
+int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
+				struct bpf_reg_state *regs);
+int btf_check_kfunc_arg_match(struct bpf_verifier_env *env,
+			      const struct btf *btf, u32 func_id,
+			      struct bpf_reg_state *regs);
 int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
 			  struct bpf_reg_state *reg);
 int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *prog,
@@ -1557,6 +1566,10 @@ struct bpf_link *bpf_link_by_id(u32 id);
 
 const struct bpf_func_proto *bpf_base_func_proto(enum bpf_func_id func_id);
 void bpf_task_storage_free(struct task_struct *task);
+bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog);
+const struct btf_func_model *
+bpf_jit_find_kfunc_model(const struct bpf_prog *prog,
+			 const struct bpf_insn *insn);
 #else /* !CONFIG_BPF_SYSCALL */
 static inline struct bpf_prog *bpf_prog_get(u32 ufd)
 {
@@ -1719,6 +1732,11 @@ static inline int bpf_prog_test_run_sk_lookup(struct bpf_prog *prog,
 	return -ENOTSUPP;
 }
 
+static inline bool bpf_prog_test_check_kfunc_call(u32 kfunc_id)
+{
+	return false;
+}
+
 static inline void bpf_map_put(struct bpf_map *map)
 {
 }
@@ -1737,6 +1755,18 @@ bpf_base_func_proto(enum bpf_func_id func_id)
 static inline void bpf_task_storage_free(struct task_struct *task)
 {
 }
+
+static inline bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
+{
+	return false;
+}
+
+static inline const struct btf_func_model *
+bpf_jit_find_kfunc_model(const struct bpf_prog *prog,
+			 const struct bpf_insn *insn)
+{
+	return NULL;
+}
 #endif /* CONFIG_BPF_SYSCALL */
 
 void __bpf_free_used_btfs(struct bpf_prog_aux *aux,

include/linux/btf.h

@@ -110,6 +110,7 @@ const struct btf_type *btf_type_resolve_func_ptr(const struct btf *btf,
 const struct btf_type *
 btf_resolve_size(const struct btf *btf, const struct btf_type *type,
 		 u32 *type_size);
+const char *btf_type_str(const struct btf_type *t);
 
 #define for_each_member(i, struct_type, member)			\
 	for (i = 0, member = btf_type_member(struct_type);	\
@@ -141,6 +142,11 @@ static inline bool btf_type_is_enum(const struct btf_type *t)
 	return BTF_INFO_KIND(t->info) == BTF_KIND_ENUM;
 }
 
+static inline bool btf_type_is_scalar(const struct btf_type *t)
+{
+	return btf_type_is_int(t) || btf_type_is_enum(t);
+}
+
 static inline bool btf_type_is_typedef(const struct btf_type *t)
 {
 	return BTF_INFO_KIND(t->info) == BTF_KIND_TYPEDEF;

include/linux/filter.h

@@ -877,8 +877,7 @@ void bpf_prog_free_linfo(struct bpf_prog *prog);
 void bpf_prog_fill_jited_linfo(struct bpf_prog *prog,
 			       const u32 *insn_to_jit_off);
 int bpf_prog_alloc_jited_linfo(struct bpf_prog *prog);
-void bpf_prog_free_jited_linfo(struct bpf_prog *prog);
-void bpf_prog_free_unused_jited_linfo(struct bpf_prog *prog);
+void bpf_prog_jit_attempt_done(struct bpf_prog *prog);
 
 struct bpf_prog *bpf_prog_alloc(unsigned int size, gfp_t gfp_extra_flags);
 struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flags);
@@ -919,6 +918,7 @@ u64 __bpf_call_base(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
 struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog);
 void bpf_jit_compile(struct bpf_prog *prog);
 bool bpf_jit_needs_zext(void);
+bool bpf_jit_supports_kfunc_call(void);
 bool bpf_helper_changes_pkt_data(void *func);
 
 static inline bool bpf_dump_raw_ok(const struct cred *cred)

include/uapi/linux/bpf.h

@@ -1117,6 +1117,10 @@ enum bpf_link_type {
  * offset to another bpf function
  */
 #define BPF_PSEUDO_CALL		1
+/* when bpf_call->src_reg == BPF_PSEUDO_KFUNC_CALL,
+ * bpf_call->imm == btf_id of a BTF_KIND_FUNC in the running kernel
+ */
+#define BPF_PSEUDO_KFUNC_CALL	2
 
 /* flags for BPF_MAP_UPDATE_ELEM command */
 enum {

kernel/bpf/btf.c

@@ -283,7 +283,7 @@ static const char * const btf_kind_str[NR_BTF_KINDS] = {
 	[BTF_KIND_FLOAT]	= "FLOAT",
 };
 
-static const char *btf_type_str(const struct btf_type *t)
+const char *btf_type_str(const struct btf_type *t)
 {
 	return btf_kind_str[BTF_INFO_KIND(t->info)];
 }
@@ -4377,7 +4377,7 @@ static u8 bpf_ctx_convert_map[] = {
 #undef BPF_LINK_TYPE
 
 static const struct btf_member *
-btf_get_prog_ctx_type(struct bpf_verifier_log *log, struct btf *btf,
+btf_get_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf,
 		      const struct btf_type *t, enum bpf_prog_type prog_type,
 		      int arg)
 {
@@ -5362,122 +5362,190 @@ int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *pr
 	return btf_check_func_type_match(log, btf1, t1, btf2, t2);
 }
 
-/* Compare BTF of a function with given bpf_reg_state.
- * Returns:
- * EFAULT - there is a verifier bug. Abort verification.
- * EINVAL - there is a type mismatch or BTF is not available.
- * 0 - BTF matches with what bpf_reg_state expects.
- * Only PTR_TO_CTX and SCALAR_VALUE states are recognized.
- */
-int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
-			     struct bpf_reg_state *regs)
+static u32 *reg2btf_ids[__BPF_REG_TYPE_MAX] = {
+#ifdef CONFIG_NET
+	[PTR_TO_SOCKET] = &btf_sock_ids[BTF_SOCK_TYPE_SOCK],
+	[PTR_TO_SOCK_COMMON] = &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
+	[PTR_TO_TCP_SOCK] = &btf_sock_ids[BTF_SOCK_TYPE_TCP],
+#endif
+};
+
+static int btf_check_func_arg_match(struct bpf_verifier_env *env,
+				    const struct btf *btf, u32 func_id,
+				    struct bpf_reg_state *regs,
+				    bool ptr_to_mem_ok)
 {
 	struct bpf_verifier_log *log = &env->log;
-	struct bpf_prog *prog = env->prog;
-	struct btf *btf = prog->aux->btf;
-	const struct btf_param *args;
+	const char *func_name, *ref_tname;
 	const struct btf_type *t, *ref_t;
-	u32 i, nargs, btf_id, type_size;
-	const char *tname;
-	bool is_global;
-
-	if (!prog->aux->func_info)
-		return -EINVAL;
-
-	btf_id = prog->aux->func_info[subprog].type_id;
-	if (!btf_id)
-		return -EFAULT;
-
-	if (prog->aux->func_info_aux[subprog].unreliable)
-		return -EINVAL;
+	const struct btf_param *args;
+	u32 i, nargs, ref_id;
 
-	t = btf_type_by_id(btf, btf_id);
+	t = btf_type_by_id(btf, func_id);
 	if (!t || !btf_type_is_func(t)) {
 		/* These checks were already done by the verifier while loading
-		 * struct bpf_func_info
+		 * struct bpf_func_info or in add_kfunc_call().
 		 */
-		bpf_log(log, "BTF of func#%d doesn't point to KIND_FUNC\n",
-			subprog);
+		bpf_log(log, "BTF of func_id %u doesn't point to KIND_FUNC\n",
+			func_id);
 		return -EFAULT;
 	}
-	tname = btf_name_by_offset(btf, t->name_off);
+	func_name = btf_name_by_offset(btf, t->name_off);
 
 	t = btf_type_by_id(btf, t->type);
 	if (!t || !btf_type_is_func_proto(t)) {
-		bpf_log(log, "Invalid BTF of func %s\n", tname);
+		bpf_log(log, "Invalid BTF of func %s\n", func_name);
 		return -EFAULT;
 	}
 	args = (const struct btf_param *)(t + 1);
 	nargs = btf_type_vlen(t);
 	if (nargs > MAX_BPF_FUNC_REG_ARGS) {
-		bpf_log(log, "Function %s has %d > %d args\n", tname, nargs,
+		bpf_log(log, "Function %s has %d > %d args\n", func_name, nargs,
 			MAX_BPF_FUNC_REG_ARGS);
-		goto out;
+		return -EINVAL;
 	}
 
-	is_global = prog->aux->func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL;
 	/* check that BTF function arguments match actual types that the
 	 * verifier sees.
 	 */
 	for (i = 0; i < nargs; i++) {
-		struct bpf_reg_state *reg = &regs[i + 1];
+		u32 regno = i + 1;
+		struct bpf_reg_state *reg = &regs[regno];
 
-		t = btf_type_by_id(btf, args[i].type);
-		while (btf_type_is_modifier(t))
-			t = btf_type_by_id(btf, t->type);
-		if (btf_type_is_int(t) || btf_type_is_enum(t)) {
+		t = btf_type_skip_modifiers(btf, args[i].type, NULL);
+		if (btf_type_is_scalar(t)) {
 			if (reg->type == SCALAR_VALUE)
 				continue;
-			bpf_log(log, "R%d is not a scalar\n", i + 1);
-			goto out;
+			bpf_log(log, "R%d is not a scalar\n", regno);
+			return -EINVAL;
 		}
-		if (btf_type_is_ptr(t)) {
+
+		if (!btf_type_is_ptr(t)) {
+			bpf_log(log, "Unrecognized arg#%d type %s\n",
+				i, btf_type_str(t));
+			return -EINVAL;
+		}
+
+		ref_t = btf_type_skip_modifiers(btf, t->type, &ref_id);
+		ref_tname = btf_name_by_offset(btf, ref_t->name_off);
+		if (btf_is_kernel(btf)) {
+			const struct btf_type *reg_ref_t;
+			const struct btf *reg_btf;
+			const char *reg_ref_tname;
+			u32 reg_ref_id;
+
+			if (!btf_type_is_struct(ref_t)) {
+				bpf_log(log, "kernel function %s args#%d pointer type %s %s is not supported\n",
+					func_name, i, btf_type_str(ref_t),
+					ref_tname);
+				return -EINVAL;
+			}
+
+			if (reg->type == PTR_TO_BTF_ID) {
+				reg_btf = reg->btf;
+				reg_ref_id = reg->btf_id;
+			} else if (reg2btf_ids[reg->type]) {
+				reg_btf = btf_vmlinux;
+				reg_ref_id = *reg2btf_ids[reg->type];
+			} else {
+				bpf_log(log, "kernel function %s args#%d expected pointer to %s %s but R%d is not a pointer to btf_id\n",
+					func_name, i,
+					btf_type_str(ref_t), ref_tname, regno);
+				return -EINVAL;
+			}
+
+			reg_ref_t = btf_type_skip_modifiers(reg_btf, reg_ref_id,
+							    &reg_ref_id);
+			reg_ref_tname = btf_name_by_offset(reg_btf,
+							   reg_ref_t->name_off);
+			if (!btf_struct_ids_match(log, reg_btf, reg_ref_id,
+						  reg->off, btf, ref_id)) {
+				bpf_log(log, "kernel function %s args#%d expected pointer to %s %s but R%d has a pointer to %s %s\n",
+					func_name, i,
+					btf_type_str(ref_t), ref_tname,
+					regno, btf_type_str(reg_ref_t),
+					reg_ref_tname);
+				return -EINVAL;
+			}
+		} else if (btf_get_prog_ctx_type(log, btf, t,
+						 env->prog->type, i)) {
 			/* If function expects ctx type in BTF check that caller
 			 * is passing PTR_TO_CTX.
 			 */
-			if (btf_get_prog_ctx_type(log, btf, t, prog->type, i)) {
-				if (reg->type != PTR_TO_CTX) {
-					bpf_log(log,
-						"arg#%d expected pointer to ctx, but got %s\n",
-						i, btf_kind_str[BTF_INFO_KIND(t->info)]);
-					goto out;
-				}
-				if (check_ctx_reg(env, reg, i + 1))
-					goto out;
-				continue;
+			if (reg->type != PTR_TO_CTX) {
+				bpf_log(log,
+					"arg#%d expected pointer to ctx, but got %s\n",
+					i, btf_type_str(t));
+				return -EINVAL;
 			}
+			if (check_ctx_reg(env, reg, regno))
+				return -EINVAL;
+		} else if (ptr_to_mem_ok) {
+			const struct btf_type *resolve_ret;
+			u32 type_size;
 
-			if (!is_global)
-				goto out;
-
-			t = btf_type_skip_modifiers(btf, t->type, NULL);
-
-			ref_t = btf_resolve_size(btf, t, &type_size);
-			if (IS_ERR(ref_t)) {
+			resolve_ret = btf_resolve_size(btf, ref_t, &type_size);
+			if (IS_ERR(resolve_ret)) {
 				bpf_log(log,
-				    "arg#%d reference type('%s %s') size cannot be determined: %ld\n",
-				    i, btf_type_str(t), btf_name_by_offset(btf, t->name_off),
-					PTR_ERR(ref_t));
-				goto out;
+					"arg#%d reference type('%s %s') size cannot be determined: %ld\n",
+					i, btf_type_str(ref_t), ref_tname,
+					PTR_ERR(resolve_ret));
+				return -EINVAL;
 			}
 
-			if (check_mem_reg(env, reg, i + 1, type_size))
-				goto out;
-
-			continue;
+			if (check_mem_reg(env, reg, regno, type_size))
+				return -EINVAL;
+		} else {
+			return -EINVAL;
 		}
-		bpf_log(log, "Unrecognized arg#%d type %s\n",
-			i, btf_kind_str[BTF_INFO_KIND(t->info)]);
-		goto out;
 	}
+
 	return 0;
-out:
+}
+
+/* Compare BTF of a function with given bpf_reg_state.
+ * Returns:
+ * EFAULT - there is a verifier bug. Abort verification.
+ * EINVAL - there is a type mismatch or BTF is not available.
+ * 0 - BTF matches with what bpf_reg_state expects.
+ * Only PTR_TO_CTX and SCALAR_VALUE states are recognized.
+ */
+int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
+				struct bpf_reg_state *regs)
+{
+	struct bpf_prog *prog = env->prog;
+	struct btf *btf = prog->aux->btf;
+	bool is_global;
+	u32 btf_id;
+	int err;
+
+	if (!prog->aux->func_info)
+		return -EINVAL;
+
+	btf_id = prog->aux->func_info[subprog].type_id;
+	if (!btf_id)
+		return -EFAULT;
+
+	if (prog->aux->func_info_aux[subprog].unreliable)
+		return -EINVAL;
+
+	is_global = prog->aux->func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL;
+	err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global);
+
 	/* Compiler optimizations can remove arguments from static functions
 	 * or mismatched type can be passed into a global function.
 	 * In such cases mark the function as unreliable from BTF point of view.
 	 */
-	prog->aux->func_info_aux[subprog].unreliable = true;
-	return -EINVAL;
+	if (err)
+		prog->aux->func_info_aux[subprog].unreliable = true;
+	return err;
+}
+
+int btf_check_kfunc_arg_match(struct bpf_verifier_env *env,
+			      const struct btf *btf, u32 func_id,
+			      struct bpf_reg_state *regs)
+{
+	return btf_check_func_arg_match(env, btf, func_id, regs, false);
 }
 
 /* Convert BTF of a function into bpf_reg_state if possible

kernel/bpf/core.c

@@ -143,25 +143,25 @@ int bpf_prog_alloc_jited_linfo(struct bpf_prog *prog)
 	if (!prog->aux->nr_linfo || !prog->jit_requested)
 		return 0;
 
-	prog->aux->jited_linfo = kcalloc(prog->aux->nr_linfo,
-					 sizeof(*prog->aux->jited_linfo),
-					 GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
+	prog->aux->jited_linfo = kvcalloc(prog->aux->nr_linfo,
+					  sizeof(*prog->aux->jited_linfo),
+					  GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
 	if (!prog->aux->jited_linfo)
 		return -ENOMEM;
 
 	return 0;
 }
 
-void bpf_prog_free_jited_linfo(struct bpf_prog *prog)
+void bpf_prog_jit_attempt_done(struct bpf_prog *prog)
 {
-	kfree(prog->aux->jited_linfo);
-	prog->aux->jited_linfo = NULL;
-}
+	if (prog->aux->jited_linfo &&
+	    (!prog->jited || !prog->aux->jited_linfo[0])) {
+		kvfree(prog->aux->jited_linfo);
+		prog->aux->jited_linfo = NULL;
+	}
 
-void bpf_prog_free_unused_jited_linfo(struct bpf_prog *prog)
-{
-	if (prog->aux->jited_linfo && !prog->aux->jited_linfo[0])
-		bpf_prog_free_jited_linfo(prog);
+	kfree(prog->aux->kfunc_tab);
+	prog->aux->kfunc_tab = NULL;
 }
 
 /* The jit engine is responsible to provide an array
@@ -217,12 +217,6 @@ void bpf_prog_fill_jited_linfo(struct bpf_prog *prog,
 			insn_to_jit_off[linfo[i].insn_off - insn_start - 1];
 }
 
-void bpf_prog_free_linfo(struct bpf_prog *prog)
-{
-	bpf_prog_free_jited_linfo(prog);
-	kvfree(prog->aux->linfo);
-}
-
 struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size,
 				  gfp_t gfp_extra_flags)
 {
@@ -1849,9 +1843,15 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_prog *fp, int *err)
 	/* In case of BPF to BPF calls, verifier did all the prep
 	 * work with regards to JITing, etc.
 	 */
+	bool jit_needed = false;
+
 	if (fp->bpf_func)
 		goto finalize;
 
+	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
+	    bpf_prog_has_kfunc_call(fp))
+		jit_needed = true;
+
 	bpf_prog_select_func(fp);
 
 	/* eBPF JITs can rewrite the program in case constant
@@ -1866,14 +1866,10 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_prog *fp, int *err)
 			return fp;
 
 		fp = bpf_int_jit_compile(fp);
-		if (!fp->jited) {
-			bpf_prog_free_jited_linfo(fp);
-#ifdef CONFIG_BPF_JIT_ALWAYS_ON
+		bpf_prog_jit_attempt_done(fp);
+		if (!fp->jited && jit_needed) {
 			*err = -ENOTSUPP;
 			return fp;
-#endif
-		} else {
-			bpf_prog_free_unused_jited_linfo(fp);
 		}
 	} else {
 		*err = bpf_prog_offload_compile(fp);
@@ -2354,6 +2350,11 @@ bool __weak bpf_jit_needs_zext(void)
 	return false;
 }
 
+bool __weak bpf_jit_supports_kfunc_call(void)
+{
+	return false;
+}
+
 /* To execute LD_ABS/LD_IND instructions __bpf_prog_run() may call
  * skb_copy_bits(), so provide a weak definition of it for NET-less config.
  */

kernel/bpf/disasm.c

@@ -19,16 +19,23 @@ static const char *__func_get_name(const struct bpf_insn_cbs *cbs,
 {
 	BUILD_BUG_ON(ARRAY_SIZE(func_id_str) != __BPF_FUNC_MAX_ID);
 
-	if (insn->src_reg != BPF_PSEUDO_CALL &&
+	if (!insn->src_reg &&
 	    insn->imm >= 0 && insn->imm < __BPF_FUNC_MAX_ID &&
 	    func_id_str[insn->imm])
 		return func_id_str[insn->imm];
 
-	if (cbs && cbs->cb_call)
-		return cbs->cb_call(cbs->private_data, insn);
+	if (cbs && cbs->cb_call) {
+		const char *res;
+
+		res = cbs->cb_call(cbs->private_data, insn);
+		if (res)
+			return res;
+	}
 
 	if (insn->src_reg == BPF_PSEUDO_CALL)
 		snprintf(buff, len, "%+d", insn->imm);
+	else if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL)
+		snprintf(buff, len, "kernel-function");
 
 	return buff;
 }

kernel/bpf/syscall.c

@@ -1694,7 +1694,9 @@ static void __bpf_prog_put_noref(struct bpf_prog *prog, bool deferred)
 {
 	bpf_prog_kallsyms_del_all(prog);
 	btf_put(prog->aux->btf);
-	bpf_prog_free_linfo(prog);
+	kvfree(prog->aux->jited_linfo);
+	kvfree(prog->aux->linfo);
+	kfree(prog->aux->kfunc_tab);
 	if (prog->aux->attach_btf)
 		btf_put(prog->aux->attach_btf);
 

net/bpf/test_run.c

@@ -2,6 +2,7 @@
 /* Copyright (c) 2017 Facebook
  */
 #include <linux/bpf.h>
+#include <linux/btf_ids.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/etherdevice.h>
@@ -213,10 +214,37 @@ int noinline bpf_modify_return_test(int a, int *b)
 	*b += 1;
 	return a + *b;
 }
+
+u64 noinline bpf_kfunc_call_test1(struct sock *sk, u32 a, u64 b, u32 c, u64 d)
+{
+	return a + b + c + d;
+}
+
+int noinline bpf_kfunc_call_test2(struct sock *sk, u32 a, u32 b)
+{
+	return a + b;
+}
+
+struct sock * noinline bpf_kfunc_call_test3(struct sock *sk)
+{
+	return sk;
+}
+
 __diag_pop();
 
 ALLOW_ERROR_INJECTION(bpf_modify_return_test, ERRNO);
 
+BTF_SET_START(test_sk_kfunc_ids)
+BTF_ID(func, bpf_kfunc_call_test1)
+BTF_ID(func, bpf_kfunc_call_test2)
+BTF_ID(func, bpf_kfunc_call_test3)
+BTF_SET_END(test_sk_kfunc_ids)
+
+bool bpf_prog_test_check_kfunc_call(u32 kfunc_id)
+{
+	return btf_id_set_contains(&test_sk_kfunc_ids, kfunc_id);
+}
+
 static void *bpf_test_init(const union bpf_attr *kattr, u32 size,
 			   u32 headroom, u32 tailroom)
 {

net/core/filter.c

@@ -9813,6 +9813,7 @@ const struct bpf_verifier_ops tc_cls_act_verifier_ops = {
 	.convert_ctx_access	= tc_cls_act_convert_ctx_access,
 	.gen_prologue		= tc_cls_act_prologue,
 	.gen_ld_abs		= bpf_gen_ld_abs,
+	.check_kfunc_call	= bpf_prog_test_check_kfunc_call,
 };
 
 const struct bpf_prog_ops tc_cls_act_prog_ops = {

net/ipv4/bpf_tcp_ca.c

@@ -5,6 +5,7 @@
 #include <linux/bpf_verifier.h>
 #include <linux/bpf.h>
 #include <linux/btf.h>
+#include <linux/btf_ids.h>
 #include <linux/filter.h>
 #include <net/tcp.h>
 #include <net/bpf_sk_storage.h>
@@ -178,10 +179,50 @@ bpf_tcp_ca_get_func_proto(enum bpf_func_id func_id,
 	}
 }
 
+BTF_SET_START(bpf_tcp_ca_kfunc_ids)
+BTF_ID(func, tcp_reno_ssthresh)
+BTF_ID(func, tcp_reno_cong_avoid)
+BTF_ID(func, tcp_reno_undo_cwnd)
+BTF_ID(func, tcp_slow_start)
+BTF_ID(func, tcp_cong_avoid_ai)
+#if IS_BUILTIN(CONFIG_TCP_CONG_CUBIC)
+BTF_ID(func, cubictcp_init)
+BTF_ID(func, cubictcp_recalc_ssthresh)
+BTF_ID(func, cubictcp_cong_avoid)
+BTF_ID(func, cubictcp_state)
+BTF_ID(func, cubictcp_cwnd_event)
+BTF_ID(func, cubictcp_acked)
+#endif
+#if IS_BUILTIN(CONFIG_TCP_CONG_DCTCP)
+BTF_ID(func, dctcp_init)
+BTF_ID(func, dctcp_update_alpha)
+BTF_ID(func, dctcp_cwnd_event)
+BTF_ID(func, dctcp_ssthresh)
+BTF_ID(func, dctcp_cwnd_undo)
+BTF_ID(func, dctcp_state)
+#endif
+#if IS_BUILTIN(CONFIG_TCP_CONG_BBR)
+BTF_ID(func, bbr_init)
+BTF_ID(func, bbr_main)
+BTF_ID(func, bbr_sndbuf_expand)
+BTF_ID(func, bbr_undo_cwnd)
+BTF_ID(func, bbr_cwnd_even),
+BTF_ID(func, bbr_ssthresh)
+BTF_ID(func, bbr_min_tso_segs)
+BTF_ID(func, bbr_set_state)
+#endif
+BTF_SET_END(bpf_tcp_ca_kfunc_ids)
+
+static bool bpf_tcp_ca_check_kfunc_call(u32 kfunc_btf_id)
+{
+	return btf_id_set_contains(&bpf_tcp_ca_kfunc_ids, kfunc_btf_id);
+}
+
 static const struct bpf_verifier_ops bpf_tcp_ca_verifier_ops = {
 	.get_func_proto		= bpf_tcp_ca_get_func_proto,
 	.is_valid_access	= bpf_tcp_ca_is_valid_access,
 	.btf_struct_access	= bpf_tcp_ca_btf_struct_access,
+	.check_kfunc_call	= bpf_tcp_ca_check_kfunc_call,
 };
 
 static int bpf_tcp_ca_init_member(const struct btf_type *t,

net/ipv4/tcp_cubic.c

@@ -124,7 +124,7 @@ static inline void bictcp_hystart_reset(struct sock *sk)
 	ca->sample_cnt = 0;
 }
 
-static void bictcp_init(struct sock *sk)
+static void cubictcp_init(struct sock *sk)
 {
 	struct bictcp *ca = inet_csk_ca(sk);
 
@@ -137,7 +137,7 @@ static void bictcp_init(struct sock *sk)
 		tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
 }
 
-static void bictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event)
+static void cubictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event)
 {
 	if (event == CA_EVENT_TX_START) {
 		struct bictcp *ca = inet_csk_ca(sk);
@@ -319,7 +319,7 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd, u32 acked)
 	ca->cnt = max(ca->cnt, 2U);
 }
 
-static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
+static void cubictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct bictcp *ca = inet_csk_ca(sk);
@@ -338,7 +338,7 @@ static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 	tcp_cong_avoid_ai(tp, ca->cnt, acked);
 }
 
-static u32 bictcp_recalc_ssthresh(struct sock *sk)
+static u32 cubictcp_recalc_ssthresh(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	struct bictcp *ca = inet_csk_ca(sk);
@@ -355,7 +355,7 @@ static u32 bictcp_recalc_ssthresh(struct sock *sk)
 	return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
 }
 
-static void bictcp_state(struct sock *sk, u8 new_state)
+static void cubictcp_state(struct sock *sk, u8 new_state)
 {
 	if (new_state == TCP_CA_Loss) {
 		bictcp_reset(inet_csk_ca(sk));
@@ -442,7 +442,7 @@ static void hystart_update(struct sock *sk, u32 delay)
 	}
 }
 
-static void bictcp_acked(struct sock *sk, const struct ack_sample *sample)
+static void cubictcp_acked(struct sock *sk, const struct ack_sample *sample)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	struct bictcp *ca = inet_csk_ca(sk);
@@ -471,13 +471,13 @@ static void bictcp_acked(struct sock *sk, const struct ack_sample *sample)
 }
 
 static struct tcp_congestion_ops cubictcp __read_mostly = {
-	.init		= bictcp_init,
-	.ssthresh	= bictcp_recalc_ssthresh,
-	.cong_avoid	= bictcp_cong_avoid,
-	.set_state	= bictcp_state,
+	.init		= cubictcp_init,
+	.ssthresh	= cubictcp_recalc_ssthresh,
+	.cong_avoid	= cubictcp_cong_avoid,
+	.set_state	= cubictcp_state,
 	.undo_cwnd	= tcp_reno_undo_cwnd,
-	.cwnd_event	= bictcp_cwnd_event,
-	.pkts_acked     = bictcp_acked,
+	.cwnd_event	= cubictcp_cwnd_event,
+	.pkts_acked     = cubictcp_acked,
 	.owner		= THIS_MODULE,
 	.name		= "cubic",
 };

tools/include/uapi/linux/bpf.h

@@ -1117,6 +1117,10 @@ enum bpf_link_type {
  * offset to another bpf function
  */
 #define BPF_PSEUDO_CALL		1
+/* when bpf_call->src_reg == BPF_PSEUDO_KFUNC_CALL,
+ * bpf_call->imm == btf_id of a BTF_KIND_FUNC in the running kernel
+ */
+#define BPF_PSEUDO_KFUNC_CALL	2
 
 /* flags for BPF_MAP_UPDATE_ELEM command */
 enum {

tools/testing/selftests/bpf/bpf_tcp_helpers.h

@@ -187,16 +187,6 @@ struct tcp_congestion_ops {
 	typeof(y) __y = (y);			\
 	__x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
 
-static __always_inline __u32 tcp_slow_start(struct tcp_sock *tp, __u32 acked)
-{
-	__u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
-
-	acked -= cwnd - tp->snd_cwnd;
-	tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
-
-	return acked;
-}
-
 static __always_inline bool tcp_in_slow_start(const struct tcp_sock *tp)
 {
 	return tp->snd_cwnd < tp->snd_ssthresh;
@@ -213,22 +203,7 @@ static __always_inline bool tcp_is_cwnd_limited(const struct sock *sk)
 	return !!BPF_CORE_READ_BITFIELD(tp, is_cwnd_limited);
 }
 
-static __always_inline void tcp_cong_avoid_ai(struct tcp_sock *tp, __u32 w, __u32 acked)
-{
-	/* If credits accumulated at a higher w, apply them gently now. */
-	if (tp->snd_cwnd_cnt >= w) {
-		tp->snd_cwnd_cnt = 0;
-		tp->snd_cwnd++;
-	}
-
-	tp->snd_cwnd_cnt += acked;
-	if (tp->snd_cwnd_cnt >= w) {
-		__u32 delta = tp->snd_cwnd_cnt / w;
-
-		tp->snd_cwnd_cnt -= delta * w;
-		tp->snd_cwnd += delta;
-	}
-	tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
-}
+extern __u32 tcp_slow_start(struct tcp_sock *tp, __u32 acked) __ksym;
+extern void tcp_cong_avoid_ai(struct tcp_sock *tp, __u32 w, __u32 acked) __ksym;
 
 #endif

tools/testing/selftests/bpf/prog_tests/kfunc_call.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include <test_progs.h>
+#include <network_helpers.h>
+#include "kfunc_call_test.skel.h"
+#include "kfunc_call_test_subprog.skel.h"
+
+static void test_main(void)
+{
+	struct kfunc_call_test *skel;
+	int prog_fd, retval, err;
+
+	skel = kfunc_call_test__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel"))
+		return;
+
+	prog_fd = bpf_program__fd(skel->progs.kfunc_call_test1);
+	err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),
+				NULL, NULL, (__u32 *)&retval, NULL);
+	ASSERT_OK(err, "bpf_prog_test_run(test1)");
+	ASSERT_EQ(retval, 12, "test1-retval");
+
+	prog_fd = bpf_program__fd(skel->progs.kfunc_call_test2);
+	err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),
+				NULL, NULL, (__u32 *)&retval, NULL);
+	ASSERT_OK(err, "bpf_prog_test_run(test2)");
+	ASSERT_EQ(retval, 3, "test2-retval");
+
+	kfunc_call_test__destroy(skel);
+}
+
+static void test_subprog(void)
+{
+	struct kfunc_call_test_subprog *skel;
+	int prog_fd, retval, err;
+
+	skel = kfunc_call_test_subprog__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel"))
+		return;
+
+	prog_fd = bpf_program__fd(skel->progs.kfunc_call_test1);
+	err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),
+				NULL, NULL, (__u32 *)&retval, NULL);
+	ASSERT_OK(err, "bpf_prog_test_run(test1)");
+	ASSERT_EQ(retval, 10, "test1-retval");
+	ASSERT_NEQ(skel->data->active_res, -1, "active_res");
+	ASSERT_EQ(skel->data->sk_state, BPF_TCP_CLOSE, "sk_state");
+
+	kfunc_call_test_subprog__destroy(skel);
+}
+
+void test_kfunc_call(void)
+{
+	if (test__start_subtest("main"))
+		test_main();
+
+	if (test__start_subtest("subprog"))
+		test_subprog();
+}

tools/testing/selftests/bpf/progs/bpf_cubic.c

@@ -174,8 +174,8 @@ static __always_inline void bictcp_hystart_reset(struct sock *sk)
  * as long as it is used in one of the func ptr
  * under SEC(".struct_ops").
  */
-SEC("struct_ops/bictcp_init")
-void BPF_PROG(bictcp_init, struct sock *sk)
+SEC("struct_ops/bpf_cubic_init")
+void BPF_PROG(bpf_cubic_init, struct sock *sk)
 {
 	struct bictcp *ca = inet_csk_ca(sk);
 
@@ -192,7 +192,7 @@ void BPF_PROG(bictcp_init, struct sock *sk)
  * The remaining tcp-cubic functions have an easier way.
  */
 SEC("no-sec-prefix-bictcp_cwnd_event")
-void BPF_PROG(bictcp_cwnd_event, struct sock *sk, enum tcp_ca_event event)
+void BPF_PROG(bpf_cubic_cwnd_event, struct sock *sk, enum tcp_ca_event event)
 {
 	if (event == CA_EVENT_TX_START) {
 		struct bictcp *ca = inet_csk_ca(sk);
@@ -384,7 +384,7 @@ static __always_inline void bictcp_update(struct bictcp *ca, __u32 cwnd,
 }
 
 /* Or simply use the BPF_STRUCT_OPS to avoid the SEC boiler plate. */
-void BPF_STRUCT_OPS(bictcp_cong_avoid, struct sock *sk, __u32 ack, __u32 acked)
+void BPF_STRUCT_OPS(bpf_cubic_cong_avoid, struct sock *sk, __u32 ack, __u32 acked)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct bictcp *ca = inet_csk_ca(sk);
@@ -403,7 +403,7 @@ void BPF_STRUCT_OPS(bictcp_cong_avoid, struct sock *sk, __u32 ack, __u32 acked)
 	tcp_cong_avoid_ai(tp, ca->cnt, acked);
 }
 
-__u32 BPF_STRUCT_OPS(bictcp_recalc_ssthresh, struct sock *sk)
+__u32 BPF_STRUCT_OPS(bpf_cubic_recalc_ssthresh, struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	struct bictcp *ca = inet_csk_ca(sk);
@@ -420,7 +420,7 @@ __u32 BPF_STRUCT_OPS(bictcp_recalc_ssthresh, struct sock *sk)
 	return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
 }
 
-void BPF_STRUCT_OPS(bictcp_state, struct sock *sk, __u8 new_state)
+void BPF_STRUCT_OPS(bpf_cubic_state, struct sock *sk, __u8 new_state)
 {
 	if (new_state == TCP_CA_Loss) {
 		bictcp_reset(inet_csk_ca(sk));
@@ -496,7 +496,7 @@ static __always_inline void hystart_update(struct sock *sk, __u32 delay)
 	}
 }
 
-void BPF_STRUCT_OPS(bictcp_acked, struct sock *sk,
+void BPF_STRUCT_OPS(bpf_cubic_acked, struct sock *sk,
 		    const struct ack_sample *sample)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
@@ -525,21 +525,21 @@ void BPF_STRUCT_OPS(bictcp_acked, struct sock *sk,
 		hystart_update(sk, delay);
 }
 
-__u32 BPF_STRUCT_OPS(tcp_reno_undo_cwnd, struct sock *sk)
-{
-	const struct tcp_sock *tp = tcp_sk(sk);
+extern __u32 tcp_reno_undo_cwnd(struct sock *sk) __ksym;
 
-	return max(tp->snd_cwnd, tp->prior_cwnd);
+__u32 BPF_STRUCT_OPS(bpf_cubic_undo_cwnd, struct sock *sk)
+{
+	return tcp_reno_undo_cwnd(sk);
 }
 
 SEC(".struct_ops")
 struct tcp_congestion_ops cubic = {
-	.init		= (void *)bictcp_init,
-	.ssthresh	= (void *)bictcp_recalc_ssthresh,
-	.cong_avoid	= (void *)bictcp_cong_avoid,
-	.set_state	= (void *)bictcp_state,
-	.undo_cwnd	= (void *)tcp_reno_undo_cwnd,
-	.cwnd_event	= (void *)bictcp_cwnd_event,
-	.pkts_acked     = (void *)bictcp_acked,
+	.init		= (void *)bpf_cubic_init,
+	.ssthresh	= (void *)bpf_cubic_recalc_ssthresh,
+	.cong_avoid	= (void *)bpf_cubic_cong_avoid,
+	.set_state	= (void *)bpf_cubic_state,
+	.undo_cwnd	= (void *)bpf_cubic_undo_cwnd,
+	.cwnd_event	= (void *)bpf_cubic_cwnd_event,
+	.pkts_acked     = (void *)bpf_cubic_acked,
 	.name		= "bpf_cubic",
 };

tools/testing/selftests/bpf/progs/bpf_dctcp.c

@@ -194,22 +194,12 @@ __u32 BPF_PROG(dctcp_cwnd_undo, struct sock *sk)
 	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
 }
 
-SEC("struct_ops/tcp_reno_cong_avoid")
-void BPF_PROG(tcp_reno_cong_avoid, struct sock *sk, __u32 ack, __u32 acked)
-{
-	struct tcp_sock *tp = tcp_sk(sk);
-
-	if (!tcp_is_cwnd_limited(sk))
-		return;
+extern void tcp_reno_cong_avoid(struct sock *sk, __u32 ack, __u32 acked) __ksym;
 
-	/* In "safe" area, increase. */
-	if (tcp_in_slow_start(tp)) {
-		acked = tcp_slow_start(tp, acked);
-		if (!acked)
-			return;
-	}
-	/* In dangerous area, increase slowly. */
-	tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
+SEC("struct_ops/dctcp_reno_cong_avoid")
+void BPF_PROG(dctcp_cong_avoid, struct sock *sk, __u32 ack, __u32 acked)
+{
+	tcp_reno_cong_avoid(sk, ack, acked);
 }
 
 SEC(".struct_ops")
@@ -226,7 +216,7 @@ struct tcp_congestion_ops dctcp = {
 	.in_ack_event   = (void *)dctcp_update_alpha,
 	.cwnd_event	= (void *)dctcp_cwnd_event,
 	.ssthresh	= (void *)dctcp_ssthresh,
-	.cong_avoid	= (void *)tcp_reno_cong_avoid,
+	.cong_avoid	= (void *)dctcp_cong_avoid,
 	.undo_cwnd	= (void *)dctcp_cwnd_undo,
 	.set_state	= (void *)dctcp_state,
 	.flags		= TCP_CONG_NEEDS_ECN,

tools/testing/selftests/bpf/progs/kfunc_call_test.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_tcp_helpers.h"
+
+extern int bpf_kfunc_call_test2(struct sock *sk, __u32 a, __u32 b) __ksym;
+extern __u64 bpf_kfunc_call_test1(struct sock *sk, __u32 a, __u64 b,
+				  __u32 c, __u64 d) __ksym;
+
+SEC("classifier")
+int kfunc_call_test2(struct __sk_buff *skb)
+{
+	struct bpf_sock *sk = skb->sk;
+
+	if (!sk)
+		return -1;
+
+	sk = bpf_sk_fullsock(sk);
+	if (!sk)
+		return -1;
+
+	return bpf_kfunc_call_test2((struct sock *)sk, 1, 2);
+}
+
+SEC("classifier")
+int kfunc_call_test1(struct __sk_buff *skb)
+{
+	struct bpf_sock *sk = skb->sk;
+	__u64 a = 1ULL << 32;
+	__u32 ret;
+
+	if (!sk)
+		return -1;
+
+	sk = bpf_sk_fullsock(sk);
+	if (!sk)
+		return -1;
+
+	a = bpf_kfunc_call_test1((struct sock *)sk, 1, a | 2, 3, a | 4);
+	ret = a >> 32;   /* ret should be 2 */
+	ret += (__u32)a; /* ret should be 12 */
+
+	return ret;
+}
+
+char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/progs/kfunc_call_test_subprog.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_tcp_helpers.h"
+
+extern const int bpf_prog_active __ksym;
+extern __u64 bpf_kfunc_call_test1(struct sock *sk, __u32 a, __u64 b,
+				  __u32 c, __u64 d) __ksym;
+extern struct sock *bpf_kfunc_call_test3(struct sock *sk) __ksym;
+int active_res = -1;
+int sk_state = -1;
+
+int __noinline f1(struct __sk_buff *skb)
+{
+	struct bpf_sock *sk = skb->sk;
+	int *active;
+
+	if (!sk)
+		return -1;
+
+	sk = bpf_sk_fullsock(sk);
+	if (!sk)
+		return -1;
+
+	active = (int *)bpf_per_cpu_ptr(&bpf_prog_active,
+					bpf_get_smp_processor_id());
+	if (active)
+		active_res = *active;
+
+	sk_state = bpf_kfunc_call_test3((struct sock *)sk)->__sk_common.skc_state;
+
+	return (__u32)bpf_kfunc_call_test1((struct sock *)sk, 1, 2, 3, 4);
+}
+
+SEC("classifier")
+int kfunc_call_test1(struct __sk_buff *skb)
+{
+	return f1(skb);
+}
+
+char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/verifier/calls.c

@@ -19,7 +19,7 @@
 	BPF_MOV64_IMM(BPF_REG_0, 2),
 	BPF_EXIT_INSN(),
 	},
-	.errstr_unpriv = "function calls to other bpf functions are allowed for",
+	.errstr_unpriv = "loading/calling other bpf or kernel functions are allowed for",
 	.result_unpriv = REJECT,
 	.result = ACCEPT,
 	.retval = 1,
@@ -136,7 +136,7 @@
 {
 	"calls: wrong src reg",
 	.insns = {
-	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 2, 0, 0),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 3, 0, 0),
 	BPF_MOV64_IMM(BPF_REG_0, 1),
 	BPF_EXIT_INSN(),
 	},
@@ -397,7 +397,7 @@
 	BPF_MOV64_IMM(BPF_REG_0, 1),
 	BPF_EXIT_INSN(),
 	},
-	.errstr_unpriv = "function calls to other bpf functions are allowed for",
+	.errstr_unpriv = "loading/calling other bpf or kernel functions are allowed for",
 	.fixup_map_hash_48b = { 3 },
 	.result_unpriv = REJECT,
 	.result = ACCEPT,
@@ -1977,7 +1977,7 @@
 	BPF_EXIT_INSN(),
 	},
 	.prog_type = BPF_PROG_TYPE_SOCKET_FILTER,
-	.errstr_unpriv = "function calls to other bpf functions are allowed for",
+	.errstr_unpriv = "loading/calling other bpf or kernel functions are allowed for",
 	.result_unpriv = REJECT,
 	.result = ACCEPT,
 },
@@ -2003,7 +2003,7 @@
 	BPF_EXIT_INSN(),
 	},
 	.prog_type = BPF_PROG_TYPE_SOCKET_FILTER,
-	.errstr_unpriv = "function calls to other bpf functions are allowed for",
+	.errstr_unpriv = "loading/calling other bpf or kernel functions are allowed for",
 	.errstr = "!read_ok",
 	.result = REJECT,
 },
@@ -2028,7 +2028,7 @@
 	BPF_EXIT_INSN(),
 	},
 	.prog_type = BPF_PROG_TYPE_SOCKET_FILTER,
-	.errstr_unpriv = "function calls to other bpf functions are allowed for",
+	.errstr_unpriv = "loading/calling other bpf or kernel functions are allowed for",
 	.errstr = "!read_ok",
 	.result = REJECT,
 },

tools/testing/selftests/bpf/verifier/dead_code.c

@@ -85,7 +85,7 @@
 	BPF_MOV64_IMM(BPF_REG_0, 12),
 	BPF_EXIT_INSN(),
 	},
-	.errstr_unpriv = "function calls to other bpf functions are allowed for",
+	.errstr_unpriv = "loading/calling other bpf or kernel functions are allowed for",
 	.result_unpriv = REJECT,
 	.result = ACCEPT,
 	.retval = 7,
@@ -103,7 +103,7 @@
 	BPF_MOV64_IMM(BPF_REG_0, 12),
 	BPF_EXIT_INSN(),
 	},
-	.errstr_unpriv = "function calls to other bpf functions are allowed for",
+	.errstr_unpriv = "loading/calling other bpf or kernel functions are allowed for",
 	.result_unpriv = REJECT,
 	.result = ACCEPT,
 	.retval = 7,
@@ -121,7 +121,7 @@
 	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 1, 0, -5),
 	BPF_EXIT_INSN(),
 	},
-	.errstr_unpriv = "function calls to other bpf functions are allowed for",
+	.errstr_unpriv = "loading/calling other bpf or kernel functions are allowed for",
 	.result_unpriv = REJECT,
 	.result = ACCEPT,
 	.retval = 7,
@@ -137,7 +137,7 @@
 	BPF_MOV64_REG(BPF_REG_0, BPF_REG_1),
 	BPF_EXIT_INSN(),
 	},
-	.errstr_unpriv = "function calls to other bpf functions are allowed for",
+	.errstr_unpriv = "loading/calling other bpf or kernel functions are allowed for",
 	.result_unpriv = REJECT,
 	.result = ACCEPT,
 	.retval = 2,
@@ -152,7 +152,7 @@
 	BPF_MOV64_REG(BPF_REG_0, BPF_REG_1),
 	BPF_EXIT_INSN(),
 	},
-	.errstr_unpriv = "function calls to other bpf functions are allowed for",
+	.errstr_unpriv = "loading/calling other bpf or kernel functions are allowed for",
 	.result_unpriv = REJECT,
 	.result = ACCEPT,
 	.retval = 2,