[PATCH bpf-next v4 1/2] bpf: Search and add kfuncs in struct_ops prologue and epilogue

[PATCH bpf-next v4 1/2] bpf: Search and add kfuncs in struct_ops prologue and epilogue

[Amery Hung]

From: Amery Hung <amery.hung@bytedance.com>

Currently, add_kfunc_call() is only invoked once before the main
verification loop. Therefore, the verifier could not find the
bpf_kfunc_btf_tab of a new kfunc call which is not seen in user defined
struct_ops operators but introduced in gen_prologue or gen_epilogue
during do_misc_fixup(). Fix this by searching kfuncs in the patching
instruction buffer and add them to prog->aux->kfunc_tab.

Signed-off-by: Amery Hung <amery.hung@bytedance.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
---
 kernel/bpf/verifier.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8f1df279e432..212b487fd39d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3215,6 +3215,21 @@ bpf_jit_find_kfunc_model(const struct bpf_prog *prog,
 	return res ? &res->func_model : NULL;
 }
 
+static int add_kfunc_in_insns(struct bpf_verifier_env *env,
+			      struct bpf_insn *insn, int cnt)
+{
+	int i, ret;
+
+	for (i = 0; i < cnt; i++, insn++) {
+		if (bpf_pseudo_kfunc_call(insn)) {
+			ret = add_kfunc_call(env, insn->imm, insn->off);
+			if (ret < 0)
+				return ret;
+		}
+	}
+	return 0;
+}
+
 static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
 {
 	struct bpf_subprog_info *subprog = env->subprog_info;
@@ -20368,7 +20383,7 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 {
 	struct bpf_subprog_info *subprogs = env->subprog_info;
 	const struct bpf_verifier_ops *ops = env->ops;
-	int i, cnt, size, ctx_field_size, delta = 0, epilogue_cnt = 0;
+	int i, cnt, size, ctx_field_size, ret, delta = 0, epilogue_cnt = 0;
 	const int insn_cnt = env->prog->len;
 	struct bpf_insn *epilogue_buf = env->epilogue_buf;
 	struct bpf_insn *insn_buf = env->insn_buf;
@@ -20397,6 +20412,10 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 				return -ENOMEM;
 			env->prog = new_prog;
 			delta += cnt - 1;
+
+			ret = add_kfunc_in_insns(env, epilogue_buf, epilogue_cnt - 1);
+			if (ret < 0)
+				return ret;
 		}
 	}
 
@@ -20417,6 +20436,10 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 
 			env->prog = new_prog;
 			delta += cnt - 1;
+
+			ret = add_kfunc_in_insns(env, insn_buf, cnt - 1);
+			if (ret < 0)
+				return ret;
 		}
 	}
 
-- 
2.47.1

[PATCH bpf-next v4 2/2] selftests/bpf: Test gen_pro/epilogue that generate kfuncs

[Amery Hung]

Test gen_prologue and gen_epilogue that generate kfuncs that have not
been seen in the main program.

The main bpf program and return value checks are identical to
pro_epilogue.c introduced in commit 47e69431b57a ("selftests/bpf: Test
gen_prologue and gen_epilogue"). However, now when bpf_testmod_st_ops
detects a program name with prefix "test_kfunc_", it generates slightly
different prologue and epilogue: They still add 1000 to args->a in
prologue, add 10000 to args->a and set r0 to 2 * args->a in epilogue,
but involve kfuncs.

At high level, the alternative version of prologue and epilogue look
like this:

  cgrp = bpf_cgroup_from_id(0);
  if (cgrp)
          bpf_cgroup_release(cgrp);
  else
          /* Perform what original bpf_testmod_st_ops prologue or
           * epilogue does
           */

Since 0 is never a valid cgroup id, the original prologue or epilogue
logic will be performed. As a result, the __retval check should expect
the exact same return value.

Signed-off-by: Amery Hung <ameryhung@gmail.com>
---
 include/linux/filter.h                        | 10 ++
 kernel/bpf/btf.c                              |  1 +
 .../selftests/bpf/prog_tests/pro_epilogue.c   |  2 +
 .../bpf/progs/pro_epilogue_with_kfunc.c       | 88 ++++++++++++++++++
 .../selftests/bpf/test_kmods/bpf_testmod.c    | 92 +++++++++++++++++++
 5 files changed, 193 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/pro_epilogue_with_kfunc.c

diff --git a/include/linux/filter.h b/include/linux/filter.h
index a3ea46281595..3ed6eb9e7c73 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -469,6 +469,16 @@ static inline bool insn_is_cast_user(const struct bpf_insn *insn)
 		.off   = 0,					\
 		.imm   = BPF_CALL_IMM(FUNC) })
 
+/* Kfunc call */
+
+#define BPF_CALL_KFUNC(OFF, IMM)				\
+	((struct bpf_insn) {					\
+		.code  = BPF_JMP | BPF_CALL,			\
+		.dst_reg = 0,					\
+		.src_reg = BPF_PSEUDO_KFUNC_CALL,		\
+		.off   = OFF,					\
+		.imm   = IMM })
+
 /* Raw code statement block */
 
 #define BPF_RAW_INSN(CODE, DST, SRC, OFF, IMM)			\
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 7a7e02dcde84..1927d7e53b5a 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -606,6 +606,7 @@ s32 bpf_find_btf_id(const char *name, u32 kind, struct btf **btf_p)
 	spin_unlock_bh(&btf_idr_lock);
 	return ret;
 }
+EXPORT_SYMBOL_GPL(bpf_find_btf_id);
 
 const struct btf_type *btf_type_skip_modifiers(const struct btf *btf,
 					       u32 id, u32 *res_id)
diff --git a/tools/testing/selftests/bpf/prog_tests/pro_epilogue.c b/tools/testing/selftests/bpf/prog_tests/pro_epilogue.c
index 509883e6823a..5d3c00a08a88 100644
--- a/tools/testing/selftests/bpf/prog_tests/pro_epilogue.c
+++ b/tools/testing/selftests/bpf/prog_tests/pro_epilogue.c
@@ -6,6 +6,7 @@
 #include "epilogue_tailcall.skel.h"
 #include "pro_epilogue_goto_start.skel.h"
 #include "epilogue_exit.skel.h"
+#include "pro_epilogue_with_kfunc.skel.h"
 
 struct st_ops_args {
 	__u64 a;
@@ -55,6 +56,7 @@ void test_pro_epilogue(void)
 	RUN_TESTS(pro_epilogue);
 	RUN_TESTS(pro_epilogue_goto_start);
 	RUN_TESTS(epilogue_exit);
+	RUN_TESTS(pro_epilogue_with_kfunc);
 	if (test__start_subtest("tailcall"))
 		test_tailcall();
 }
diff --git a/tools/testing/selftests/bpf/progs/pro_epilogue_with_kfunc.c b/tools/testing/selftests/bpf/progs/pro_epilogue_with_kfunc.c
new file mode 100644
index 000000000000..a5a8f08ac8fb
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/pro_epilogue_with_kfunc.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+#include "../test_kmods/bpf_testmod.h"
+#include "../test_kmods/bpf_testmod_kfunc.h"
+
+char _license[] SEC("license") = "GPL";
+
+void __kfunc_btf_root(void)
+{
+	bpf_kfunc_st_ops_inc10(NULL);
+}
+
+static __noinline __used int subprog(struct st_ops_args *args)
+{
+	args->a += 1;
+	return args->a;
+}
+
+__success
+/* prologue */
+__xlated("0: r8 = r1")
+__xlated("1: r1 = 0")
+__xlated("2: call kernel-function")
+__xlated("3: if r0 != 0x0 goto pc+5")
+__xlated("4: r6 = *(u64 *)(r8 +0)")
+__xlated("5: r7 = *(u64 *)(r6 +0)")
+__xlated("6: r7 += 1000")
+__xlated("7: *(u64 *)(r6 +0) = r7")
+__xlated("8: goto pc+2")
+__xlated("9: r1 = r0")
+__xlated("10: call kernel-function")
+__xlated("11: r1 = r8")
+/* save __u64 *ctx to stack */
+__xlated("12: *(u64 *)(r10 -8) = r1")
+/* main prog */
+__xlated("13: r1 = *(u64 *)(r1 +0)")
+__xlated("14: r6 = r1")
+__xlated("15: call kernel-function")
+__xlated("16: r1 = r6")
+__xlated("17: call pc+")
+/* epilogue */
+__xlated("18: r1 = 0")
+__xlated("19: r6 = 0")
+__xlated("20: call kernel-function")
+__xlated("21: if r0 != 0x0 goto pc+6")
+__xlated("22: r1 = *(u64 *)(r10 -8)")
+__xlated("23: r1 = *(u64 *)(r1 +0)")
+__xlated("24: r6 = *(u64 *)(r1 +0)")
+__xlated("25: r6 += 10000")
+__xlated("26: *(u64 *)(r1 +0) = r6")
+__xlated("27: goto pc+2")
+__xlated("28: r1 = r0")
+__xlated("29: call kernel-function")
+__xlated("30: r0 = r6")
+__xlated("31: r0 *= 2")
+__xlated("32: exit")
+SEC("struct_ops/test_pro_epilogue")
+__naked int test_kfunc_pro_epilogue(void)
+{
+	asm volatile (
+	"r1 = *(u64 *)(r1 +0);"
+	"r6 = r1;"
+	"call %[bpf_kfunc_st_ops_inc10];"
+	"r1 = r6;"
+	"call subprog;"
+	"exit;"
+	:
+	: __imm(bpf_kfunc_st_ops_inc10)
+	: __clobber_all);
+}
+
+SEC("syscall")
+__retval(22022) /* (PROLOGUE_A [1000] + KFUNC_INC10 + SUBPROG_A [1] + EPILOGUE_A [10000]) * 2 */
+int syscall_pro_epilogue(void *ctx)
+{
+	struct st_ops_args args = {};
+
+	return bpf_kfunc_st_ops_test_pro_epilogue(&args);
+}
+
+SEC(".struct_ops.link")
+struct bpf_testmod_st_ops pro_epilogue_with_kfunc = {
+	.test_pro_epilogue = (void *)test_kfunc_pro_epilogue,
+};
diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
index 578bfc40dd05..7a107eb9872a 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
@@ -1309,6 +1309,85 @@ static int bpf_test_mod_st_ops__test_pro_epilogue(struct st_ops_args *args)
 	return 0;
 }
 
+static int bpf_cgroup_from_id_id;
+static int bpf_cgroup_release_id;
+
+static int st_ops_gen_prologue_with_kfunc(struct bpf_insn *insn_buf, bool direct_write,
+					  const struct bpf_prog *prog)
+{
+	struct bpf_insn *insn = insn_buf;
+
+	/* r8 = r1; // r8 will be "u64 *ctx".
+	 * r1 = 0;
+	 * r0 = bpf_cgroup_from_id(r1);
+	 * if r0 != 0 goto pc+5;
+	 * r6 = r8[0]; // r6 will be "struct st_ops *args".
+	 * r7 = r6->a;
+	 * r7 += 1000;
+	 * r6->a = r7;
+	 * goto pc+2;
+	 * r1 = r0;
+	 * bpf_cgroup_release(r1);
+	 * r1 = r8;
+	 */
+	*insn++ = BPF_MOV64_REG(BPF_REG_8, BPF_REG_1);
+	*insn++ = BPF_MOV64_IMM(BPF_REG_1, 0);
+	*insn++ = BPF_CALL_KFUNC(0, bpf_cgroup_from_id_id);
+	*insn++ = BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 5);
+	*insn++ = BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_8, 0);
+	*insn++ = BPF_LDX_MEM(BPF_DW, BPF_REG_7, BPF_REG_6, offsetof(struct st_ops_args, a));
+	*insn++ = BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, 1000);
+	*insn++ = BPF_STX_MEM(BPF_DW, BPF_REG_6, BPF_REG_7, offsetof(struct st_ops_args, a));
+	*insn++ = BPF_JMP_IMM(BPF_JA, 0, 0, 2);
+	*insn++ = BPF_MOV64_REG(BPF_REG_1, BPF_REG_0);
+	*insn++ = BPF_CALL_KFUNC(0, bpf_cgroup_release_id),
+	*insn++ = BPF_MOV64_REG(BPF_REG_1, BPF_REG_8);
+	*insn++ = prog->insnsi[0];
+
+	return insn - insn_buf;
+}
+
+static int st_ops_gen_epilogue_with_kfunc(struct bpf_insn *insn_buf, const struct bpf_prog *prog,
+					  s16 ctx_stack_off)
+{
+	struct bpf_insn *insn = insn_buf;
+
+	/* r1 = 0;
+	 * r6 = 0;
+	 * r0 = bpf_cgroup_from_id(r1);
+	 * if r0 != 0 goto pc+6;
+	 * r1 = stack[ctx_stack_off]; // r1 will be "u64 *ctx"
+	 * r1 = r1[0]; // r1 will be "struct st_ops *args"
+	 * r6 = r1->a;
+	 * r6 += 10000;
+	 * r1->a = r6;
+	 * goto pc+2
+	 * r1 = r0;
+	 * bpf_cgroup_release(r1);
+	 * r0 = r6;
+	 * r0 *= 2;
+	 * BPF_EXIT;
+	 */
+	*insn++ = BPF_MOV64_IMM(BPF_REG_1, 0);
+	*insn++ = BPF_MOV64_IMM(BPF_REG_6, 0);
+	*insn++ = BPF_CALL_KFUNC(0, bpf_cgroup_from_id_id);
+	*insn++ = BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 6);
+	*insn++ = BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_FP, ctx_stack_off);
+	*insn++ = BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_1, 0);
+	*insn++ = BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, offsetof(struct st_ops_args, a));
+	*insn++ = BPF_ALU64_IMM(BPF_ADD, BPF_REG_6, 10000);
+	*insn++ = BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_6, offsetof(struct st_ops_args, a));
+	*insn++ = BPF_JMP_IMM(BPF_JA, 0, 0, 2);
+	*insn++ = BPF_MOV64_REG(BPF_REG_1, BPF_REG_0);
+	*insn++ = BPF_CALL_KFUNC(0, bpf_cgroup_release_id),
+	*insn++ = BPF_MOV64_REG(BPF_REG_0, BPF_REG_6);
+	*insn++ = BPF_ALU64_IMM(BPF_MUL, BPF_REG_0, 2);
+	*insn++ = BPF_EXIT_INSN();
+
+	return insn - insn_buf;
+}
+
+#define KFUNC_PRO_EPI_PREFIX "test_kfunc_"
 static int st_ops_gen_prologue(struct bpf_insn *insn_buf, bool direct_write,
 			       const struct bpf_prog *prog)
 {
@@ -1318,6 +1397,9 @@ static int st_ops_gen_prologue(struct bpf_insn *insn_buf, bool direct_write,
 	    strcmp(prog->aux->attach_func_name, "test_pro_epilogue"))
 		return 0;
 
+	if (!strncmp(prog->aux->name, KFUNC_PRO_EPI_PREFIX, strlen(KFUNC_PRO_EPI_PREFIX)))
+		return st_ops_gen_prologue_with_kfunc(insn_buf, direct_write, prog);
+
 	/* r6 = r1[0]; // r6 will be "struct st_ops *args". r1 is "u64 *ctx".
 	 * r7 = r6->a;
 	 * r7 += 1000;
@@ -1341,6 +1423,9 @@ static int st_ops_gen_epilogue(struct bpf_insn *insn_buf, const struct bpf_prog
 	    strcmp(prog->aux->attach_func_name, "test_pro_epilogue"))
 		return 0;
 
+	if (!strncmp(prog->aux->name, KFUNC_PRO_EPI_PREFIX, strlen(KFUNC_PRO_EPI_PREFIX)))
+		return st_ops_gen_epilogue_with_kfunc(insn_buf, prog, ctx_stack_off);
+
 	/* r1 = stack[ctx_stack_off]; // r1 will be "u64 *ctx"
 	 * r1 = r1[0]; // r1 will be "struct st_ops *args"
 	 * r6 = r1->a;
@@ -1411,6 +1496,13 @@ static void st_ops_unreg(void *kdata, struct bpf_link *link)
 
 static int st_ops_init(struct btf *btf)
 {
+	struct btf *kfunc_btf;
+
+	bpf_cgroup_from_id_id = bpf_find_btf_id("bpf_cgroup_from_id", BTF_KIND_FUNC, &kfunc_btf);
+	bpf_cgroup_release_id = bpf_find_btf_id("bpf_cgroup_release", BTF_KIND_FUNC, &kfunc_btf);
+	if (!bpf_cgroup_from_id_id || !bpf_cgroup_release_id)
+		return -EINVAL;
+
 	return 0;
 }
 
-- 
2.47.1

Re: [PATCH bpf-next v4 1/2] bpf: Search and add kfuncs in struct_ops prologue and epilogue

[Martin KaFai Lau]

On 2/25/25 1:29 PM, Amery Hung wrote:
> From: Amery Hung <amery.hung@bytedance.com>
> 
> Currently, add_kfunc_call() is only invoked once before the main
> verification loop. Therefore, the verifier could not find the
> bpf_kfunc_btf_tab of a new kfunc call which is not seen in user defined
> struct_ops operators but introduced in gen_prologue or gen_epilogue
> during do_misc_fixup(). Fix this by searching kfuncs in the patching
> instruction buffer and add them to prog->aux->kfunc_tab.

Acked-by: Martin KaFai Lau <martin.lau@kernel.org>

Re: [PATCH bpf-next v4 2/2] selftests/bpf: Test gen_pro/epilogue that generate kfuncs

[Martin KaFai Lau]

On 2/25/25 1:29 PM, Amery Hung wrote:
> @@ -1411,6 +1496,13 @@ static void st_ops_unreg(void *kdata, struct bpf_link *link)
>   
>   static int st_ops_init(struct btf *btf)
>   {
> +	struct btf *kfunc_btf;
> +
> +	bpf_cgroup_from_id_id = bpf_find_btf_id("bpf_cgroup_from_id", BTF_KIND_FUNC, &kfunc_btf);
> +	bpf_cgroup_release_id = bpf_find_btf_id("bpf_cgroup_release", BTF_KIND_FUNC, &kfunc_btf);
> +	if (!bpf_cgroup_from_id_id || !bpf_cgroup_release_id)

Just noticed this. This should be "< 0" check. No need for "== 0" check because 
"id == 0" is reserved for "void" which is not BTF_KIND_FUNC.

With that,

Acked-by: Martin KaFai Lau <martin.lau@kernel.org>

Re: [PATCH bpf-next v4 2/2] selftests/bpf: Test gen_pro/epilogue that generate kfuncs

[Amery Hung]

On Tue, Feb 25, 2025 at 1:58 PM Martin KaFai Lau <martin.lau@linux.dev> wrote:
>
> On 2/25/25 1:29 PM, Amery Hung wrote:
> > @@ -1411,6 +1496,13 @@ static void st_ops_unreg(void *kdata, struct bpf_link *link)
> >
> >   static int st_ops_init(struct btf *btf)
> >   {
> > +     struct btf *kfunc_btf;
> > +
> > +     bpf_cgroup_from_id_id = bpf_find_btf_id("bpf_cgroup_from_id", BTF_KIND_FUNC, &kfunc_btf);
> > +     bpf_cgroup_release_id = bpf_find_btf_id("bpf_cgroup_release", BTF_KIND_FUNC, &kfunc_btf);
> > +     if (!bpf_cgroup_from_id_id || !bpf_cgroup_release_id)
>
> Just noticed this. This should be "< 0" check. No need for "== 0" check because
> "id == 0" is reserved for "void" which is not BTF_KIND_FUNC.
>

I should be more careful about this. I will send another version.

Thank you,
Amery

> With that,
>
> Acked-by: Martin KaFai Lau <martin.lau@kernel.org>