[PATCH bpf-next v7 0/2] Introduce jit_required to prevent a kernel panic

[PATCH bpf-next v7 0/2] Introduce jit_required to prevent a kernel panic

[Tiezhu Yang]

This series introduces a 'jit_required' flag in struct bpf_prog
to track programs that strictly require JIT.

The aim is to reject loading programs with inlined helpers when
JIT is unavailable to prevent a kernel panic.

Tiezhu Yang (2):
  bpf: Introduce jit_required flag and refactor kfunc path
  bpf: Reject programs with inlined helpers if JIT is unavailable

 include/linux/bpf.h   | 3 ++-
 kernel/bpf/core.c     | 3 +--
 kernel/bpf/fixups.c   | 4 +++-
 kernel/bpf/verifier.c | 2 ++
 4 files changed, 8 insertions(+), 4 deletions(-)

-- 
2.42.0

[PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[Tiezhu Yang]

Introduce a 'jit_required' bitfield flag at the end of the
flags group in struct bpf_prog. This bit tracks whether a
program strictly requires the JIT compiler.

Set this flag to 1 when a kfunc call is added at the end of
bpf_add_kfunc_call().

In __bpf_prog_select_runtime(), check with fp->jit_required
rather than bpf_prog_has_kfunc_call() to unify the logic.

Suggested-by: Alexei Starovoitov <ast@kernel.org>
Suggested-by: KaFai Wan <kafai.wan@linux.dev>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 include/linux/bpf.h   | 3 ++-
 kernel/bpf/core.c     | 3 +--
 kernel/bpf/verifier.c | 2 ++
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index ba09795e0bfd..4e2b059d71f3 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1880,7 +1880,8 @@ struct bpf_prog {
 				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 */
+				sleepable:1,	/* BPF program is sleepable */
+				jit_required:1;	/* program strictly requires JIT compiler */
 	enum bpf_prog_type	type;		/* Type of BPF program */
 	enum bpf_attach_type	expected_attach_type; /* For some prog types */
 	u32			len;		/* Number of filter blocks */
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 649cce41e13f..5fcd19ccb41a 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2619,8 +2619,7 @@ struct bpf_prog *__bpf_prog_select_runtime(struct bpf_verifier_env *env, struct
 	if (fp->bpf_func)
 		goto finalize;
 
-	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
-	    bpf_prog_has_kfunc_call(fp))
+	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || fp->jit_required)
 		jit_needed = true;
 
 	if (!bpf_prog_select_interpreter(fp))
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 25aea4271cd0..f496b45b9da4 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2765,6 +2765,8 @@ int bpf_add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, u16 offset)
 	desc->func_model = func_model;
 	sort(tab->descs, tab->nr_descs, sizeof(tab->descs[0]),
 	     kfunc_desc_cmp_by_id_off, NULL);
+
+	env->prog->jit_required = 1;
 	return 0;
 }
 
-- 
2.42.0

[PATCH bpf-next v7 2/2] bpf: Reject programs with inlined helpers if JIT is unavailable

[Tiezhu Yang]

When an architecture implements bpf_jit_inlines_helper_call() (such as
LoongArch, ARM64, PowerPC, and RISC-V), the verifier skips rewriting the
helper call offset (insn->imm) during the bpf_do_misc_fixups() phase,
because the helper is expected to be inlined by the JIT compiler. As a
result, insn->imm remains as the raw helper enum ID.

However, if JIT is disabled at runtime (net.core.bpf_jit_enable=0) or
if the JIT compilation later dynamically fails (e.g., due to OOM), the
core BPF subsystem falls back to the BPF interpreter.

When the interpreter executes (__bpf_call_base + insn->imm) with the
unpatched raw helper ID, it jumps into an unaligned invalid address
space, triggering an instruction alignment fault or a memory access
panic.

Fix this by setting 'jit_required' to 1 when helper call rewriting is
skipped for JIT inlining. During runtime selection, if JIT compilation
is not available, explicitly reject loading with -ENOTSUPP based on
this flag to safely prevent the kernel panic.

Fixes: 2ddec2c80b44 ("riscv, bpf: inline bpf_get_smp_processor_id()")
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Suggested-by: KaFai Wan <kafai.wan@linux.dev>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 kernel/bpf/fixups.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/fixups.c b/kernel/bpf/fixups.c
index 12a8a4eb757f..94e0457a0aa3 100644
--- a/kernel/bpf/fixups.c
+++ b/kernel/bpf/fixups.c
@@ -1841,8 +1841,10 @@ int bpf_do_misc_fixups(struct bpf_verifier_env *env)
 		}
 
 		/* Skip inlining the helper call if the JIT does it. */
-		if (bpf_jit_inlines_helper_call(insn->imm))
+		if (bpf_jit_inlines_helper_call(insn->imm)) {
+			prog->jit_required = 1;
 			goto next_insn;
+		}
 
 		if (insn->imm == BPF_FUNC_get_route_realm)
 			prog->dst_needed = 1;
-- 
2.42.0

Re: [PATCH bpf-next v7 2/2] bpf: Reject programs with inlined helpers if JIT is unavailable

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] The patch prevents loading BPF programs that use JIT-inlined helpers (e.g., `bpf_get_smp_processor_id`) when the BPF JIT is explicitly disabled at load time (`net.core.bpf_jit_enable=0`).
--

commit 01713d8606e656f4dadefe493f371f4c861d842b
Author: Tiezhu Yang <yangtiezhu@loongson.cn>

bpf: Reject programs with inlined helpers if JIT is unavailable

This patch sets the jit_required flag to 1 when a BPF program uses helpers
that are expected to be inlined by the JIT compiler. This prevents a kernel
panic in the BPF interpreter by rejecting the program with -ENOTSUPP if
JIT compilation is unavailable at runtime.

> diff --git a/kernel/bpf/fixups.c b/kernel/bpf/fixups.c
> index 12a8a4eb757f1..94e0457a0aa33 100644
> --- a/kernel/bpf/fixups.c
> +++ b/kernel/bpf/fixups.c
> @@ -1841,8 +1841,10 @@ int bpf_do_misc_fixups(struct bpf_verifier_env *env)
>  		}
>  
>  		/* Skip inlining the helper call if the JIT does it. */
> -		if (bpf_jit_inlines_helper_call(insn->imm))
> +		if (bpf_jit_inlines_helper_call(insn->imm)) {
> +			prog->jit_required = 1;
>  			goto next_insn;
> +		}

[Severity: High]
While this correctly prevents the interpreter panic, does this unconditionally
reject valid BPF programs when the JIT is explicitly disabled at load time
(e.g., net.core.bpf_jit_enable=0)?

If this block checked prog->jit_requested before skipping the fixup and
setting jit_required, wouldn't the verifier properly patch the instruction
when JIT is disabled, allowing the program to execute successfully in the
interpreter?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260702143656.28845-1-yangtiezhu@loongson.cn?part=2

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The `bpf_fixup_call_args()` function and `bpf_prog_has_kfunc_call()` macro were not updated to use the new `jit_required` flag, leading to inconsistent interpreter fallback behavior for pruned kfuncs.
--

commit 5a3f8861c2b6916fe194f97a407cb7265f545fd0
Author: Tiezhu Yang <yangtiezhu@loongson.cn>

bpf: Introduce jit_required flag and refactor kfunc path

Introduce a 'jit_required' bitfield flag at the end of the
flags group in struct bpf_prog. This bit tracks whether a
program strictly requires the JIT compiler.

> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 649cce41e13f3..5fcd19ccb41a9 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2619,8 +2619,7 @@ struct bpf_prog *__bpf_prog_select_runtime(struct bpf_verifier_env *env, struct
>  	if (fp->bpf_func)
>  		goto finalize;
>  
> -	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
> -	    bpf_prog_has_kfunc_call(fp))
> +	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || fp->jit_required)
>  		jit_needed = true;
>  
>  	if (!bpf_prog_select_interpreter(fp))

[Severity: Medium]
Since bpf_prog_has_kfunc_call() was replaced here with fp->jit_required,
should bpf_fixup_call_args() in kernel/bpf/fixups.c also be updated to use
the new flag?

Currently, bpf_fixup_call_args() still calls bpf_prog_has_kfunc_call(). If
a program has a pruned kfunc (allocating kfunc_tab but leaving
jit_required=0) and JIT falls back to the interpreter, wouldn't
bpf_fixup_call_args() incorrectly reject the program with -EINVAL?

kernel/bpf/fixups.c:bpf_fixup_call_args() {
    ...
	bool has_kfunc_call = bpf_prog_has_kfunc_call(prog);
    ...
	if (has_kfunc_call) {
		verbose(env, "calling kernel functions are not allowed in non-JITed programs\n");
		return -EINVAL;
	}
    ...
}

Should bpf_prog_has_kfunc_call() in kernel/bpf/verifier.c be updated to
check prog->jit_required, or removed entirely in favor of checking the flag
directly?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260702143656.28845-1-yangtiezhu@loongson.cn?part=1

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[Tiezhu Yang]

On 2026/7/2 下午10:58, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] The `bpf_fixup_call_args()` function and `bpf_prog_has_kfunc_call()` macro were not updated to use the new `jit_required` flag, leading to inconsistent interpreter fallback behavior for pruned kfuncs.
> --
> 
> commit 5a3f8861c2b6916fe194f97a407cb7265f545fd0
> Author: Tiezhu Yang <yangtiezhu@loongson.cn>
> 
> bpf: Introduce jit_required flag and refactor kfunc path
> 
> Introduce a 'jit_required' bitfield flag at the end of the
> flags group in struct bpf_prog. This bit tracks whether a
> program strictly requires the JIT compiler.
> 
>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>> index 649cce41e13f3..5fcd19ccb41a9 100644
>> --- a/kernel/bpf/core.c
>> +++ b/kernel/bpf/core.c
>> @@ -2619,8 +2619,7 @@ struct bpf_prog *__bpf_prog_select_runtime(struct bpf_verifier_env *env, struct
>>   	if (fp->bpf_func)
>>   		goto finalize;
>>   
>> -	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
>> -	    bpf_prog_has_kfunc_call(fp))
>> +	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || fp->jit_required)
>>   		jit_needed = true;
>>   
>>   	if (!bpf_prog_select_interpreter(fp))
> 
> [Severity: Medium]
> Since bpf_prog_has_kfunc_call() was replaced here with fp->jit_required,
> should bpf_fixup_call_args() in kernel/bpf/fixups.c also be updated to use
> the new flag?
> 
> Currently, bpf_fixup_call_args() still calls bpf_prog_has_kfunc_call(). If
> a program has a pruned kfunc (allocating kfunc_tab but leaving
> jit_required=0) and JIT falls back to the interpreter, wouldn't
> bpf_fixup_call_args() incorrectly reject the program with -EINVAL?
> 
> kernel/bpf/fixups.c:bpf_fixup_call_args() {
>      ...
> 	bool has_kfunc_call = bpf_prog_has_kfunc_call(prog);
>      ...
> 	if (has_kfunc_call) {
> 		verbose(env, "calling kernel functions are not allowed in non-JITed programs\n");
> 		return -EINVAL;
> 	}
>      ...
> }
> 
> Should bpf_prog_has_kfunc_call() in kernel/bpf/verifier.c be updated to
> check prog->jit_required, or removed entirely in favor of checking the flag
> directly?

I think it is wrong to remove bpf_prog_has_kfunc_call() entirely,
because using prog->jit_required directly in bpf_fixup_call_args()
would cause false positives.

I tested the following changes:

```
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 4e2b059d71f3..3a2fc194e2bb 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3171,7 +3171,6 @@ const struct bpf_func_proto 
*bpf_base_func_proto(enum bpf_func_id func_id,
                                                  const struct bpf_prog 
*prog);
  void bpf_task_storage_free(struct task_struct *task);
  void bpf_cgrp_storage_free(struct cgroup *cgroup);
-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);
@@ -3510,11 +3509,6 @@ 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)
diff --git a/kernel/bpf/fixups.c b/kernel/bpf/fixups.c
index 94e0457a0aa3..7fb92b5fa415 100644
--- a/kernel/bpf/fixups.c
+++ b/kernel/bpf/fixups.c
@@ -1378,7 +1378,6 @@ int bpf_fixup_call_args(struct bpf_verifier_env *env)
  #ifndef CONFIG_BPF_JIT_ALWAYS_ON
         struct bpf_prog *prog = env->prog;
         struct bpf_insn *insn = prog->insnsi;
-       bool has_kfunc_call = bpf_prog_has_kfunc_call(prog);
         int depth;
  #endif
         int i, err = 0;
@@ -1404,7 +1403,7 @@ int bpf_fixup_call_args(struct bpf_verifier_env *env)
                         return err;
         }
  #ifndef CONFIG_BPF_JIT_ALWAYS_ON
-       if (has_kfunc_call) {
+       if (prog->jit_required) {
                 verbose(env, "calling kernel functions are not allowed 
in non-JITed programs\n");
                 return -EINVAL;
         }
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f496b45b9da4..3dbed3047254 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2770,11 +2770,6 @@ int bpf_add_kfunc_call(struct bpf_verifier_env 
*env, u32 func_id, u16 offset)
         return 0;
  }

-bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
-{
-       return !!prog->aux->kfunc_tab;
-}
-
  static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
  {
         struct bpf_subprog_info *subprog = env->subprog_info;
```

Here is the local test log:

```
fedora@linux:~$ cat test_panic.c
   #include <linux/bpf.h>
   #include <bpf/bpf_helpers.h>

   SEC("kprobe/sys_getpid")
   int test_panic(void *ctx)
   {
   	struct task_struct *task;

   	task = (struct task_struct *)bpf_get_current_task();
   	if (task)
   		bpf_printk("Task address: %p\n", task);

   	return 0;
   }

   char LICENSE[] SEC("license") = "GPL";
fedora@linux:~$ clang -target bpf -O2 -g -c test_panic.c -o test_panic.o
fedora@linux:~$ sudo sysctl -w net.core.bpf_jit_enable=0
[sudo] password for fedora:
net.core.bpf_jit_enable = 0
fedora@linux:~$ sudo bpftool prog load test_panic.o 
/sys/fs/bpf/test_panic autoattach
libbpf: prog 'test_panic': BPF program load failed: Invalid argument
libbpf: prog 'test_panic': -- BEGIN PROG LOAD LOG --
calling kernel functions are not allowed in non-JITed programs
processed 10 insns (limit 1000000) max_states_per_insn 0 total_states 1 
peak_states 1 mark_read 0
-- END PROG LOAD LOG --
libbpf: prog 'test_panic': failed to load: -22
libbpf: failed to load object 'test_panic.o'
Error: failed to load object file
```

This change incorrectly rejects programs that only contain normal
inlined helper calls with -EINVAL.

Instead, I think bpf_prog_has_kfunc_call() should be updated to check
prog->jit_required, like so:

```
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f496b45b9da4..1f5824c1c691 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2772,7 +2772,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env 
*env, u32 func_id, u16 offset)

  bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
  {
-       return !!prog->aux->kfunc_tab;
+       return prog->jit_required && !!prog->aux->kfunc_tab;
  }

  static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
```

Here is the local test log:

```
fedora@linux:~$ cat test_panic.c
   #include <linux/bpf.h>
   #include <bpf/bpf_helpers.h>

   SEC("kprobe/sys_getpid")
   int test_panic(void *ctx)
   {
   	struct task_struct *task;

   	task = (struct task_struct *)bpf_get_current_task();
   	if (task)
   		bpf_printk("Task address: %p\n", task);

   	return 0;
   }

   char LICENSE[] SEC("license") = "GPL";
fedora@linux:~$ clang -target bpf -O2 -g -c test_panic.c -o test_panic.o
fedora@linux:~$ sudo sysctl -w net.core.bpf_jit_enable=0
[sudo] password for fedora:
net.core.bpf_jit_enable = 0
fedora@linux:~$ sudo bpftool prog load test_panic.o 
/sys/fs/bpf/test_panic autoattach
libbpf: prog 'test_panic': BPF program load failed: unknown error (-524)
libbpf: prog 'test_panic': -- BEGIN PROG LOAD LOG --
processed 10 insns (limit 1000000) max_states_per_insn 0 total_states 1 
peak_states 1 mark_read 0
-- END PROG LOAD LOG --
libbpf: prog 'test_panic': failed to load: -524
libbpf: failed to load object 'test_panic.o'
Error: failed to load object file
```

This ensures that pruned kfuncs (allocating kfunc_tab but leaving
jit_required=0) safely return false, at the same time, this check
perfectly isolates normal inlined helper paths.

Let me wait for more review comments and will send v8 next week.

Thanks,
Tiezhu

Re: [PATCH bpf-next v7 2/2] bpf: Reject programs with inlined helpers if JIT is unavailable

[Tiezhu Yang]

On 2026/7/2 下午10:57, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] The patch prevents loading BPF programs that use JIT-inlined helpers (e.g., `bpf_get_smp_processor_id`) when the BPF JIT is explicitly disabled at load time (`net.core.bpf_jit_enable=0`).
> --
> 
> commit 01713d8606e656f4dadefe493f371f4c861d842b
> Author: Tiezhu Yang <yangtiezhu@loongson.cn>
> 
> bpf: Reject programs with inlined helpers if JIT is unavailable
> 
> This patch sets the jit_required flag to 1 when a BPF program uses helpers
> that are expected to be inlined by the JIT compiler. This prevents a kernel
> panic in the BPF interpreter by rejecting the program with -ENOTSUPP if
> JIT compilation is unavailable at runtime.
> 
>> diff --git a/kernel/bpf/fixups.c b/kernel/bpf/fixups.c
>> index 12a8a4eb757f1..94e0457a0aa33 100644
>> --- a/kernel/bpf/fixups.c
>> +++ b/kernel/bpf/fixups.c
>> @@ -1841,8 +1841,10 @@ int bpf_do_misc_fixups(struct bpf_verifier_env *env)
>>   		}
>>   
>>   		/* Skip inlining the helper call if the JIT does it. */
>> -		if (bpf_jit_inlines_helper_call(insn->imm))
>> +		if (bpf_jit_inlines_helper_call(insn->imm)) {
>> +			prog->jit_required = 1;
>>   			goto next_insn;
>> +		}
> 
> [Severity: High]
> While this correctly prevents the interpreter panic, does this unconditionally
> reject valid BPF programs when the JIT is explicitly disabled at load time
> (e.g., net.core.bpf_jit_enable=0)?

Yes.

> If this block checked prog->jit_requested before skipping the fixup and
> setting jit_required, wouldn't the verifier properly patch the instruction
> when JIT is disabled, allowing the program to execute successfully in the
> interpreter?

No, this was already explored in earlier version (v4), but it was
explicitly rejected by the BPF maintainer.

If JIT is unavailable, rejecting the program load with -ENOTSUPP is
the intended design.

Thanks,
Tiezhu

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[Leon Hwang]

On 3/7/26 10:57, Tiezhu Yang wrote:
> On 2026/7/2 下午10:58, sashiko-bot@kernel.org wrote:
[...]
>>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>>> index 649cce41e13f3..5fcd19ccb41a9 100644
>>> --- a/kernel/bpf/core.c
>>> +++ b/kernel/bpf/core.c
>>> @@ -2619,8 +2619,7 @@ struct bpf_prog
>>> *__bpf_prog_select_runtime(struct bpf_verifier_env *env, struct
>>>       if (fp->bpf_func)
>>>           goto finalize;
>>>   -    if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
>>> -        bpf_prog_has_kfunc_call(fp))
>>> +    if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || fp->jit_required)
>>>           jit_needed = true;
>>>         if (!bpf_prog_select_interpreter(fp))
>>
>> [Severity: Medium]
>> Since bpf_prog_has_kfunc_call() was replaced here with fp->jit_required,
>> should bpf_fixup_call_args() in kernel/bpf/fixups.c also be updated to
>> use
>> the new flag?
>>
>> Currently, bpf_fixup_call_args() still calls
>> bpf_prog_has_kfunc_call(). If
>> a program has a pruned kfunc (allocating kfunc_tab but leaving
>> jit_required=0) and JIT falls back to the interpreter, wouldn't
>> bpf_fixup_call_args() incorrectly reject the program with -EINVAL?


I think this rejection is intentional. '!!prog->aux->kfunc_tab' means
there is kfunc call in the prog, even though the kfunc call could be pruned.

>>
>> kernel/bpf/fixups.c:bpf_fixup_call_args() {
>>      ...
>>     bool has_kfunc_call = bpf_prog_has_kfunc_call(prog);
>>      ...
>>     if (has_kfunc_call) {
>>         verbose(env, "calling kernel functions are not allowed in non-
>> JITed programs\n");
>>         return -EINVAL;
>>     }
>>      ...
>> }

[...]

> ```
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index f496b45b9da4..1f5824c1c691 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2772,7 +2772,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env
> *env, u32 func_id, u16 offset)
> 
>  bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
>  {
> -       return !!prog->aux->kfunc_tab;
> +       return prog->jit_required && !!prog->aux->kfunc_tab;


When 'prog->jit_required' is used for JIT-inlineable helper call, this
change could also cause false positive for the above pruned kfunc case.

If you don't want bpf_fixup_call_args() rejects the program with -EINVAL
for the pruned kfunc case, suggest moving 'if (!func_id && !offset)'
before the tab allocation in bpf_add_kfunc_call().

Thanks,
Leon

>  }
> [...]

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[Tiezhu Yang]

On 2026/7/3 下午1:24, Leon Hwang wrote:
> On 3/7/26 10:57, Tiezhu Yang wrote:
>> On 2026/7/2 下午10:58, sashiko-bot@kernel.org wrote:
> [...]
>>>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>>>> index 649cce41e13f3..5fcd19ccb41a9 100644
>>>> --- a/kernel/bpf/core.c
>>>> +++ b/kernel/bpf/core.c
>>>> @@ -2619,8 +2619,7 @@ struct bpf_prog
>>>> *__bpf_prog_select_runtime(struct bpf_verifier_env *env, struct
>>>>        if (fp->bpf_func)
>>>>            goto finalize;
>>>>    -    if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
>>>> -        bpf_prog_has_kfunc_call(fp))
>>>> +    if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || fp->jit_required)
>>>>            jit_needed = true;
>>>>          if (!bpf_prog_select_interpreter(fp))
>>>
>>> [Severity: Medium]
>>> Since bpf_prog_has_kfunc_call() was replaced here with fp->jit_required,
>>> should bpf_fixup_call_args() in kernel/bpf/fixups.c also be updated to
>>> use
>>> the new flag?
>>>
>>> Currently, bpf_fixup_call_args() still calls
>>> bpf_prog_has_kfunc_call(). If
>>> a program has a pruned kfunc (allocating kfunc_tab but leaving
>>> jit_required=0) and JIT falls back to the interpreter, wouldn't
>>> bpf_fixup_call_args() incorrectly reject the program with -EINVAL?
> 
> 
> I think this rejection is intentional. '!!prog->aux->kfunc_tab' means
> there is kfunc call in the prog, even though the kfunc call could be pruned.
> 
>>>
>>> kernel/bpf/fixups.c:bpf_fixup_call_args() {
>>>       ...
>>>      bool has_kfunc_call = bpf_prog_has_kfunc_call(prog);
>>>       ...
>>>      if (has_kfunc_call) {
>>>          verbose(env, "calling kernel functions are not allowed in non-
>>> JITed programs\n");
>>>          return -EINVAL;
>>>      }
>>>       ...
>>> }
> 
> [...]
> 
>> ```
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index f496b45b9da4..1f5824c1c691 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -2772,7 +2772,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env
>> *env, u32 func_id, u16 offset)
>>
>>   bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
>>   {
>> -       return !!prog->aux->kfunc_tab;
>> +       return prog->jit_required && !!prog->aux->kfunc_tab;
> 
> 
> When 'prog->jit_required' is used for JIT-inlineable helper call, this
> change could also cause false positive for the above pruned kfunc case.
> 
> If you don't want bpf_fixup_call_args() rejects the program with -EINVAL
> for the pruned kfunc case, suggest moving 'if (!func_id && !offset)'
> before the tab allocation in bpf_add_kfunc_call().

How about this:

```
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 25aea4271cd0..c34cc524651a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2770,7 +2770,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env 
*env, u32 func_id, u16 offset)

  bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
  {
-       return !!prog->aux->kfunc_tab;
+       return prog->aux->kfunc_tab && prog->aux->kfunc_tab->nr_descs > 0;
  }

  static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
```
IMO, there are no side effects for the following four cases:

1. Pure JIT-inlined Helper
2. Pure Pruned kfunc
3. Pruned kfunc + Inlined Helper
4. Active (Unpruned) kfunc

Thanks,
Tiezhu

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[KaFai Wan]

On Fri, 2026-07-03 at 10:57 +0800, Tiezhu Yang wrote:
> On 2026/7/2 下午10:58, sashiko-bot@kernel.org wrote:
> > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> > - [Medium] The `bpf_fixup_call_args()` function and `bpf_prog_has_kfunc_call()` macro were not
> > updated to use the new `jit_required` flag, leading to inconsistent interpreter fallback
> > behavior for pruned kfuncs.
> > --
> > 
> > commit 5a3f8861c2b6916fe194f97a407cb7265f545fd0
> > Author: Tiezhu Yang <yangtiezhu@loongson.cn>
> > 
> > bpf: Introduce jit_required flag and refactor kfunc path
> > 
> > Introduce a 'jit_required' bitfield flag at the end of the
> > flags group in struct bpf_prog. This bit tracks whether a
> > program strictly requires the JIT compiler.
> > 
> > > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> > > index 649cce41e13f3..5fcd19ccb41a9 100644
> > > --- a/kernel/bpf/core.c
> > > +++ b/kernel/bpf/core.c
> > > @@ -2619,8 +2619,7 @@ struct bpf_prog *__bpf_prog_select_runtime(struct bpf_verifier_env *env,
> > > struct
> > >   	if (fp->bpf_func)
> > >   		goto finalize;
> > >   
> > > -	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
> > > -	    bpf_prog_has_kfunc_call(fp))
> > > +	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || fp->jit_required)
> > >   		jit_needed = true;
> > >   
> > >   	if (!bpf_prog_select_interpreter(fp))
> > 
> > [Severity: Medium]
> > Since bpf_prog_has_kfunc_call() was replaced here with fp->jit_required,
> > should bpf_fixup_call_args() in kernel/bpf/fixups.c also be updated to use
> > the new flag?
> > 
> > Currently, bpf_fixup_call_args() still calls bpf_prog_has_kfunc_call(). If
> > a program has a pruned kfunc (allocating kfunc_tab but leaving
> > jit_required=0) and JIT falls back to the interpreter, wouldn't
> > bpf_fixup_call_args() incorrectly reject the program with -EINVAL?
> > 
> > kernel/bpf/fixups.c:bpf_fixup_call_args() {
> >      ...
> > 	bool has_kfunc_call = bpf_prog_has_kfunc_call(prog);
> >      ...
> > 	if (has_kfunc_call) {
> > 		verbose(env, "calling kernel functions are not allowed in non-JITed
> > programs\n");
> > 		return -EINVAL;
> > 	}
> >      ...
> > }
> > 
> > Should bpf_prog_has_kfunc_call() in kernel/bpf/verifier.c be updated to
> > check prog->jit_required, or removed entirely in favor of checking the flag
> > directly?
> 
> I think it is wrong to remove bpf_prog_has_kfunc_call() entirely,

I think it is ok to remove bpf_prog_has_kfunc_call() but with some changes. see below.

> because using prog->jit_required directly in bpf_fixup_call_args()
> would cause false positives.
> 
> I tested the following changes:
> 
> ```
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 4e2b059d71f3..3a2fc194e2bb 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -3171,7 +3171,6 @@ const struct bpf_func_proto 
> *bpf_base_func_proto(enum bpf_func_id func_id,
>                                                   const struct bpf_prog 
> *prog);
>   void bpf_task_storage_free(struct task_struct *task);
>   void bpf_cgrp_storage_free(struct cgroup *cgroup);
> -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);
> @@ -3510,11 +3509,6 @@ 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)
> diff --git a/kernel/bpf/fixups.c b/kernel/bpf/fixups.c
> index 94e0457a0aa3..7fb92b5fa415 100644
> --- a/kernel/bpf/fixups.c
> +++ b/kernel/bpf/fixups.c
> @@ -1378,7 +1378,6 @@ int bpf_fixup_call_args(struct bpf_verifier_env *env)
>   #ifndef CONFIG_BPF_JIT_ALWAYS_ON
>          struct bpf_prog *prog = env->prog;
>          struct bpf_insn *insn = prog->insnsi;
> -       bool has_kfunc_call = bpf_prog_has_kfunc_call(prog);
>          int depth;
>   #endif
>          int i, err = 0;
> @@ -1404,7 +1403,7 @@ int bpf_fixup_call_args(struct bpf_verifier_env *env)
>                          return err;
>          }
>   #ifndef CONFIG_BPF_JIT_ALWAYS_ON
> -       if (has_kfunc_call) {
> +       if (prog->jit_required) {
>                  verbose(env, "calling kernel functions are not allowed 
> in non-JITed programs\n");

we can change the log for general purpose. patch #2 and future case will hit this too.

>                  return -EINVAL;
>          }
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index f496b45b9da4..3dbed3047254 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2770,11 +2770,6 @@ int bpf_add_kfunc_call(struct bpf_verifier_env 
> *env, u32 func_id, u16 offset)
>          return 0;
>   }
> 
> -bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
> -{
> -       return !!prog->aux->kfunc_tab;
> -}
> -
>   static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
>   {
>          struct bpf_subprog_info *subprog = env->subprog_info;
> ```
> 
> Here is the local test log:
> 
> ```
> fedora@linux:~$ cat test_panic.c
>    #include <linux/bpf.h>
>    #include <bpf/bpf_helpers.h>
> 
>    SEC("kprobe/sys_getpid")
>    int test_panic(void *ctx)
>    {
>    	struct task_struct *task;
> 
>    	task = (struct task_struct *)bpf_get_current_task();
>    	if (task)
>    		bpf_printk("Task address: %p\n", task);
> 
>    	return 0;
>    }
> 
>    char LICENSE[] SEC("license") = "GPL";
> fedora@linux:~$ clang -target bpf -O2 -g -c test_panic.c -o test_panic.o
> fedora@linux:~$ sudo sysctl -w net.core.bpf_jit_enable=0
> [sudo] password for fedora:
> net.core.bpf_jit_enable = 0
> fedora@linux:~$ sudo bpftool prog load test_panic.o 
> /sys/fs/bpf/test_panic autoattach
> libbpf: prog 'test_panic': BPF program load failed: Invalid argument
> libbpf: prog 'test_panic': -- BEGIN PROG LOAD LOG --
> calling kernel functions are not allowed in non-JITed programs
> processed 10 insns (limit 1000000) max_states_per_insn 0 total_states 1 
> peak_states 1 mark_read 0
> -- END PROG LOAD LOG --
> libbpf: prog 'test_panic': failed to load: -22
> libbpf: failed to load object 'test_panic.o'
> Error: failed to load object file
> ```
> 
> This change incorrectly rejects programs that only contain normal
> inlined helper calls with -EINVAL.

Was it tested after compiling together with patch #2? seems patch #2 works.

> 
> Instead, I think bpf_prog_has_kfunc_call() should be updated to check
> prog->jit_required, like so:
> 
> ```
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index f496b45b9da4..1f5824c1c691 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2772,7 +2772,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env 
> *env, u32 func_id, u16 offset)
> 
>   bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
>   {
> -       return !!prog->aux->kfunc_tab;
> +       return prog->jit_required && !!prog->aux->kfunc_tab;

bpf_get_current_task() is a helper, not kfunc. test_panic has no kfunc, prog->aux->kfunc_tab
is null. so we get -ENOTSUPP(-524)

>   }
> 
>   static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
> ```
> 
> Here is the local test log:
> 
> ```
> fedora@linux:~$ cat test_panic.c
>    #include <linux/bpf.h>
>    #include <bpf/bpf_helpers.h>
> 
>    SEC("kprobe/sys_getpid")
>    int test_panic(void *ctx)
>    {
>    	struct task_struct *task;
> 
>    	task = (struct task_struct *)bpf_get_current_task();
>    	if (task)
>    		bpf_printk("Task address: %p\n", task);
> 
>    	return 0;
>    }
> 
>    char LICENSE[] SEC("license") = "GPL";
> fedora@linux:~$ clang -target bpf -O2 -g -c test_panic.c -o test_panic.o
> fedora@linux:~$ sudo sysctl -w net.core.bpf_jit_enable=0
> [sudo] password for fedora:
> net.core.bpf_jit_enable = 0
> fedora@linux:~$ sudo bpftool prog load test_panic.o 
> /sys/fs/bpf/test_panic autoattach
> libbpf: prog 'test_panic': BPF program load failed: unknown error (-524)
> libbpf: prog 'test_panic': -- BEGIN PROG LOAD LOG --
> processed 10 insns (limit 1000000) max_states_per_insn 0 total_states 1 
> peak_states 1 mark_read 0
> -- END PROG LOAD LOG --
> libbpf: prog 'test_panic': failed to load: -524
> libbpf: failed to load object 'test_panic.o'
> Error: failed to load object file
> ```
> 
> This ensures that pruned kfuncs (allocating kfunc_tab but leaving
> jit_required=0) safely return false, at the same time, this check
> perfectly isolates normal inlined helper paths.

pruned kfuncs well handled in patch [1], see details in check_kfunc_call() and fixup_kfunc_call().

[1] https://lore.kernel.org/bpf/20211002011757.311265-3-memxor@gmail.com/
> 
> Let me wait for more review comments and will send v8 next week.
> 
> Thanks,
> Tiezhu
> 

-- 
Thanks,
KaFai

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[KaFai Wan]

On Thu, 2026-07-02 at 22:36 +0800, Tiezhu Yang wrote:
> Introduce a 'jit_required' bitfield flag at the end of the
> flags group in struct bpf_prog. This bit tracks whether a
> program strictly requires the JIT compiler.
> 
> Set this flag to 1 when a kfunc call is added at the end of
> bpf_add_kfunc_call().
> 
> In __bpf_prog_select_runtime(), check with fp->jit_required
> rather than bpf_prog_has_kfunc_call() to unify the logic.
> 
> Suggested-by: Alexei Starovoitov <ast@kernel.org>
> Suggested-by: KaFai Wan <kafai.wan@linux.dev>
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> ---
>  include/linux/bpf.h   | 3 ++-
>  kernel/bpf/core.c     | 3 +--
>  kernel/bpf/verifier.c | 2 ++
>  3 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index ba09795e0bfd..4e2b059d71f3 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1880,7 +1880,8 @@ struct bpf_prog {
>  				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 */
> +				sleepable:1,	/* BPF program is sleepable */
> +				jit_required:1;	/* program strictly requires JIT compiler
> */

In v6 you're using 'u8 jit_required', I thought it would be 'u8 jit_required:1', so we use one byte
and left 3 byte hole for future use.

This version left 2 bytes hole, same as v5, but it can easily be misleading because of the u16 type,
since we used 17 bits. I prefer v5, it has better readability.

>  	enum bpf_prog_type	type;		/* Type of BPF program */
>  	enum bpf_attach_type	expected_attach_type; /* For some prog types */
>  	u32			len;		/* Number of filter blocks */
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 649cce41e13f..5fcd19ccb41a 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2619,8 +2619,7 @@ struct bpf_prog *__bpf_prog_select_runtime(struct bpf_verifier_env *env,
> struct
>  	if (fp->bpf_func)
>  		goto finalize;
>  
> -	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
> -	    bpf_prog_has_kfunc_call(fp))
> +	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || fp->jit_required)
>  		jit_needed = true;
>  
>  	if (!bpf_prog_select_interpreter(fp))
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 25aea4271cd0..f496b45b9da4 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2765,6 +2765,8 @@ int bpf_add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, u16
> offset)
>  	desc->func_model = func_model;
>  	sort(tab->descs, tab->nr_descs, sizeof(tab->descs[0]),
>  	     kfunc_desc_cmp_by_id_off, NULL);
> +
> +	env->prog->jit_required = 1;

That's ok, and I think Sashiko is right about this patch.

>  	return 0;
>  }
>  

-- 
Thanks,
KaFai

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[Leon Hwang]

On 2026/7/3 14:59, Tiezhu Yang wrote:
[...]
>>> ```
>>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>>> index f496b45b9da4..1f5824c1c691 100644
>>> --- a/kernel/bpf/verifier.c
>>> +++ b/kernel/bpf/verifier.c
>>> @@ -2772,7 +2772,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env
>>> *env, u32 func_id, u16 offset)
>>>
>>>   bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
>>>   {
>>> -       return !!prog->aux->kfunc_tab;
>>> +       return prog->jit_required && !!prog->aux->kfunc_tab;
>>
>>
>> When 'prog->jit_required' is used for JIT-inlineable helper call, this
>> change could also cause false positive for the above pruned kfunc case.
>>
>> If you don't want bpf_fixup_call_args() rejects the program with -EINVAL
>> for the pruned kfunc case, suggest moving 'if (!func_id && !offset)'
>> before the tab allocation in bpf_add_kfunc_call().
> 
> How about this:
> 
> ```
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 25aea4271cd0..c34cc524651a 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2770,7 +2770,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env
> *env, u32 func_id, u16 offset)
> 
>  bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
>  {
> -       return !!prog->aux->kfunc_tab;
> +       return prog->aux->kfunc_tab && prog->aux->kfunc_tab->nr_descs > 0;


NIT: drop '> 0'

Looks better.

>  }
> 
>  static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
> ```
> IMO, there are no side effects for the following four cases:
> 
> 1. Pure JIT-inlined Helper
> 2. Pure Pruned kfunc
> 3. Pruned kfunc + Inlined Helper
> 4. Active (Unpruned) kfunc
> 

This change allows pruned kfunc + interpreter fallback and pruned kfunc
+ bpf_fixup_call_args(), when CONFIG_BPF_JIT_ALWAYS_ON is off.

Does it look like a pre-existing issue?

Pls read "Support kernel module function calls from eBPF" [1] to
understand the background of introducing func_id=0 kfunc.

[1] https://lore.kernel.org/bpf/20211002011757.311265-1-memxor@gmail.com/

Thanks,
Leon

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[Tiezhu Yang]

On 7/3/26 22:14, Leon Hwang wrote:
> On 2026/7/3 14:59, Tiezhu Yang wrote:
> [...]
>>>> ```
>>>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>>>> index f496b45b9da4..1f5824c1c691 100644
>>>> --- a/kernel/bpf/verifier.c
>>>> +++ b/kernel/bpf/verifier.c
>>>> @@ -2772,7 +2772,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env
>>>> *env, u32 func_id, u16 offset)
>>>>
>>>>    bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
>>>>    {
>>>> -       return !!prog->aux->kfunc_tab;
>>>> +       return prog->jit_required && !!prog->aux->kfunc_tab;
>>>
>>>
>>> When 'prog->jit_required' is used for JIT-inlineable helper call, this
>>> change could also cause false positive for the above pruned kfunc case.
>>>
>>> If you don't want bpf_fixup_call_args() rejects the program with -EINVAL
>>> for the pruned kfunc case, suggest moving 'if (!func_id && !offset)'
>>> before the tab allocation in bpf_add_kfunc_call().
>>
>> How about this:
>>
>> ```
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index 25aea4271cd0..c34cc524651a 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -2770,7 +2770,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env
>> *env, u32 func_id, u16 offset)
>>
>>   bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
>>   {
>> -       return !!prog->aux->kfunc_tab;
>> +       return prog->aux->kfunc_tab && prog->aux->kfunc_tab->nr_descs > 0;
> 
> 
> NIT: drop '> 0'
> 
> Looks better.

OK, will do it in v8.

> 
>>   }
>>
>>   static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
>> ```
>> IMO, there are no side effects for the following four cases:
>>
>> 1. Pure JIT-inlined Helper
>> 2. Pure Pruned kfunc
>> 3. Pruned kfunc + Inlined Helper
>> 4. Active (Unpruned) kfunc
>>
> 
> This change allows pruned kfunc + interpreter fallback and pruned kfunc
> + bpf_fixup_call_args(), when CONFIG_BPF_JIT_ALWAYS_ON is off.
> 
> Does it look like a pre-existing issue?

I think so.

> 
> Pls read "Support kernel module function calls from eBPF" [1] to
> understand the background of introducing func_id=0 kfunc.
> 
> [1] https://lore.kernel.org/bpf/20211002011757.311265-1-memxor@gmail.com/
> 
> Thanks,
> Leon

Thanks,
Tiezhu

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[Tiezhu Yang]

On 7/3/26 21:51, KaFai Wan wrote:
> On Fri, 2026-07-03 at 10:57 +0800, Tiezhu Yang wrote:
>> On 2026/7/2 下午10:58, sashiko-bot@kernel.org wrote:
>>> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
>>> - [Medium] The `bpf_fixup_call_args()` function and `bpf_prog_has_kfunc_call()` macro were not
>>> updated to use the new `jit_required` flag, leading to inconsistent interpreter fallback
>>> behavior for pruned kfuncs.
>>> --
>>>
>>> commit 5a3f8861c2b6916fe194f97a407cb7265f545fd0
>>> Author: Tiezhu Yang <yangtiezhu@loongson.cn>
>>>
>>> bpf: Introduce jit_required flag and refactor kfunc path
>>>
>>> Introduce a 'jit_required' bitfield flag at the end of the
>>> flags group in struct bpf_prog. This bit tracks whether a
>>> program strictly requires the JIT compiler.
>>>
>>>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>>>> index 649cce41e13f3..5fcd19ccb41a9 100644
>>>> --- a/kernel/bpf/core.c
>>>> +++ b/kernel/bpf/core.c
>>>> @@ -2619,8 +2619,7 @@ struct bpf_prog *__bpf_prog_select_runtime(struct bpf_verifier_env *env,
>>>> struct
>>>>    	if (fp->bpf_func)
>>>>    		goto finalize;
>>>>    
>>>> -	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
>>>> -	    bpf_prog_has_kfunc_call(fp))
>>>> +	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || fp->jit_required)
>>>>    		jit_needed = true;
>>>>    
>>>>    	if (!bpf_prog_select_interpreter(fp))
>>>
>>> [Severity: Medium]
>>> Since bpf_prog_has_kfunc_call() was replaced here with fp->jit_required,
>>> should bpf_fixup_call_args() in kernel/bpf/fixups.c also be updated to use
>>> the new flag?
>>>
>>> Currently, bpf_fixup_call_args() still calls bpf_prog_has_kfunc_call(). If
>>> a program has a pruned kfunc (allocating kfunc_tab but leaving
>>> jit_required=0) and JIT falls back to the interpreter, wouldn't
>>> bpf_fixup_call_args() incorrectly reject the program with -EINVAL?
>>>
>>> kernel/bpf/fixups.c:bpf_fixup_call_args() {
>>>       ...
>>> 	bool has_kfunc_call = bpf_prog_has_kfunc_call(prog);
>>>       ...
>>> 	if (has_kfunc_call) {
>>> 		verbose(env, "calling kernel functions are not allowed in non-JITed
>>> programs\n");
>>> 		return -EINVAL;
>>> 	}
>>>       ...
>>> }
>>>
>>> Should bpf_prog_has_kfunc_call() in kernel/bpf/verifier.c be updated to
>>> check prog->jit_required, or removed entirely in favor of checking the flag
>>> directly?
>>
>> I think it is wrong to remove bpf_prog_has_kfunc_call() entirely,
> 
> I think it is ok to remove bpf_prog_has_kfunc_call() but with some changes. see below.
> 
>> because using prog->jit_required directly in bpf_fixup_call_args()
>> would cause false positives.
>>
>> I tested the following changes:
>>
>> ```
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index 4e2b059d71f3..3a2fc194e2bb 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
>> @@ -3171,7 +3171,6 @@ const struct bpf_func_proto
>> *bpf_base_func_proto(enum bpf_func_id func_id,
>>                                                    const struct bpf_prog
>> *prog);
>>    void bpf_task_storage_free(struct task_struct *task);
>>    void bpf_cgrp_storage_free(struct cgroup *cgroup);
>> -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);
>> @@ -3510,11 +3509,6 @@ 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)
>> diff --git a/kernel/bpf/fixups.c b/kernel/bpf/fixups.c
>> index 94e0457a0aa3..7fb92b5fa415 100644
>> --- a/kernel/bpf/fixups.c
>> +++ b/kernel/bpf/fixups.c
>> @@ -1378,7 +1378,6 @@ int bpf_fixup_call_args(struct bpf_verifier_env *env)
>>    #ifndef CONFIG_BPF_JIT_ALWAYS_ON
>>           struct bpf_prog *prog = env->prog;
>>           struct bpf_insn *insn = prog->insnsi;
>> -       bool has_kfunc_call = bpf_prog_has_kfunc_call(prog);
>>           int depth;
>>    #endif
>>           int i, err = 0;
>> @@ -1404,7 +1403,7 @@ int bpf_fixup_call_args(struct bpf_verifier_env *env)
>>                           return err;
>>           }
>>    #ifndef CONFIG_BPF_JIT_ALWAYS_ON
>> -       if (has_kfunc_call) {
>> +       if (prog->jit_required) {
>>                   verbose(env, "calling kernel functions are not allowed
>> in non-JITed programs\n");
> 
> we can change the log for general purpose. patch #2 and future case will hit this too.
> 
>>                   return -EINVAL;
>>           }
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index f496b45b9da4..3dbed3047254 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -2770,11 +2770,6 @@ int bpf_add_kfunc_call(struct bpf_verifier_env
>> *env, u32 func_id, u16 offset)
>>           return 0;
>>    }
>>
>> -bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
>> -{
>> -       return !!prog->aux->kfunc_tab;
>> -}
>> -
>>    static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
>>    {
>>           struct bpf_subprog_info *subprog = env->subprog_info;
>> ```
>>
>> Here is the local test log:
>>
>> ```
>> fedora@linux:~$ cat test_panic.c
>>     #include <linux/bpf.h>
>>     #include <bpf/bpf_helpers.h>
>>
>>     SEC("kprobe/sys_getpid")
>>     int test_panic(void *ctx)
>>     {
>>     	struct task_struct *task;
>>
>>     	task = (struct task_struct *)bpf_get_current_task();
>>     	if (task)
>>     		bpf_printk("Task address: %p\n", task);
>>
>>     	return 0;
>>     }
>>
>>     char LICENSE[] SEC("license") = "GPL";
>> fedora@linux:~$ clang -target bpf -O2 -g -c test_panic.c -o test_panic.o
>> fedora@linux:~$ sudo sysctl -w net.core.bpf_jit_enable=0
>> [sudo] password for fedora:
>> net.core.bpf_jit_enable = 0
>> fedora@linux:~$ sudo bpftool prog load test_panic.o
>> /sys/fs/bpf/test_panic autoattach
>> libbpf: prog 'test_panic': BPF program load failed: Invalid argument
>> libbpf: prog 'test_panic': -- BEGIN PROG LOAD LOG --
>> calling kernel functions are not allowed in non-JITed programs
>> processed 10 insns (limit 1000000) max_states_per_insn 0 total_states 1
>> peak_states 1 mark_read 0
>> -- END PROG LOAD LOG --
>> libbpf: prog 'test_panic': failed to load: -22
>> libbpf: failed to load object 'test_panic.o'
>> Error: failed to load object file
>> ```
>>
>> This change incorrectly rejects programs that only contain normal
>> inlined helper calls with -EINVAL.
> 
> Was it tested after compiling together with patch #2? seems patch #2 works.

Yes.

>>
>> Instead, I think bpf_prog_has_kfunc_call() should be updated to check
>> prog->jit_required, like so:
>>
>> ```
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index f496b45b9da4..1f5824c1c691 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -2772,7 +2772,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env
>> *env, u32 func_id, u16 offset)
>>
>>    bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
>>    {
>> -       return !!prog->aux->kfunc_tab;
>> +       return prog->jit_required && !!prog->aux->kfunc_tab;
> 
> bpf_get_current_task() is a helper, not kfunc. test_panic has no kfunc, prog->aux->kfunc_tab
> is null. so we get -ENOTSUPP(-524)

Yes, I tested it.

>>    }
>>
>>    static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
>> ```
>>
>> Here is the local test log:
>>
>> ```
>> fedora@linux:~$ cat test_panic.c
>>     #include <linux/bpf.h>
>>     #include <bpf/bpf_helpers.h>
>>
>>     SEC("kprobe/sys_getpid")
>>     int test_panic(void *ctx)
>>     {
>>     	struct task_struct *task;
>>
>>     	task = (struct task_struct *)bpf_get_current_task();
>>     	if (task)
>>     		bpf_printk("Task address: %p\n", task);
>>
>>     	return 0;
>>     }
>>
>>     char LICENSE[] SEC("license") = "GPL";
>> fedora@linux:~$ clang -target bpf -O2 -g -c test_panic.c -o test_panic.o
>> fedora@linux:~$ sudo sysctl -w net.core.bpf_jit_enable=0
>> [sudo] password for fedora:
>> net.core.bpf_jit_enable = 0
>> fedora@linux:~$ sudo bpftool prog load test_panic.o
>> /sys/fs/bpf/test_panic autoattach
>> libbpf: prog 'test_panic': BPF program load failed: unknown error (-524)
>> libbpf: prog 'test_panic': -- BEGIN PROG LOAD LOG --
>> processed 10 insns (limit 1000000) max_states_per_insn 0 total_states 1
>> peak_states 1 mark_read 0
>> -- END PROG LOAD LOG --
>> libbpf: prog 'test_panic': failed to load: -524
>> libbpf: failed to load object 'test_panic.o'
>> Error: failed to load object file
>> ```
>>
>> This ensures that pruned kfuncs (allocating kfunc_tab but leaving
>> jit_required=0) safely return false, at the same time, this check
>> perfectly isolates normal inlined helper paths.
> 
> pruned kfuncs well handled in patch [1], see details in check_kfunc_call() and fixup_kfunc_call().
> 
> [1] https://lore.kernel.org/bpf/20211002011757.311265-3-memxor@gmail.com/
>>
>> Let me wait for more review comments and will send v8 next week.

Thanks,
Tiezhu

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[Tiezhu Yang]

On 7/3/26 21:55, KaFai Wan wrote:
> On Thu, 2026-07-02 at 22:36 +0800, Tiezhu Yang wrote:
>> Introduce a 'jit_required' bitfield flag at the end of the
>> flags group in struct bpf_prog. This bit tracks whether a
>> program strictly requires the JIT compiler.
>>
>> Set this flag to 1 when a kfunc call is added at the end of
>> bpf_add_kfunc_call().
>>
>> In __bpf_prog_select_runtime(), check with fp->jit_required
>> rather than bpf_prog_has_kfunc_call() to unify the logic.
>>
>> Suggested-by: Alexei Starovoitov <ast@kernel.org>
>> Suggested-by: KaFai Wan <kafai.wan@linux.dev>
>> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
>> ---
>>   include/linux/bpf.h   | 3 ++-
>>   kernel/bpf/core.c     | 3 +--
>>   kernel/bpf/verifier.c | 2 ++
>>   3 files changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index ba09795e0bfd..4e2b059d71f3 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
>> @@ -1880,7 +1880,8 @@ struct bpf_prog {
>>   				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 */
>> +				sleepable:1,	/* BPF program is sleepable */
>> +				jit_required:1;	/* program strictly requires JIT compiler
>> */
> 
> In v6 you're using 'u8 jit_required', I thought it would be 'u8 jit_required:1', so we use one byte
> and left 3 byte hole for future use.
> 
> This version left 2 bytes hole, same as v5, but it can easily be misleading because of the u16 type,
> since we used 17 bits. I prefer v5, it has better readability.

OK, I will use the previous layout in v8, like this:

```
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index ba09795e0bfd..463fae6a5c33 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1865,8 +1865,9 @@ struct bpf_prog_aux {

  struct bpf_prog {
  	u16			pages;		/* Number of allocated pages */
-	u16			jited:1,	/* Is our filter JIT'ed? */
+	u32			jited:1,	/* Is our filter JIT'ed? */
  				jit_requested:1,/* archs need to JIT the prog */
+				jit_required:1, /* program strictly requires JIT compiler */
  				gpl_compatible:1, /* Is filter GPL compatible? */
  				cb_access:1,	/* Is control block accessed? */
  				dst_needed:1,	/* Do we need dst entry? */
```

> 
>>   	enum bpf_prog_type	type;		/* Type of BPF program */
>>   	enum bpf_attach_type	expected_attach_type; /* For some prog types */
>>   	u32			len;		/* Number of filter blocks */
>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>> index 649cce41e13f..5fcd19ccb41a 100644
>> --- a/kernel/bpf/core.c
>> +++ b/kernel/bpf/core.c
>> @@ -2619,8 +2619,7 @@ struct bpf_prog *__bpf_prog_select_runtime(struct bpf_verifier_env *env,
>> struct
>>   	if (fp->bpf_func)
>>   		goto finalize;
>>   
>> -	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
>> -	    bpf_prog_has_kfunc_call(fp))
>> +	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || fp->jit_required)
>>   		jit_needed = true;
>>   
>>   	if (!bpf_prog_select_interpreter(fp))
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index 25aea4271cd0..f496b45b9da4 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -2765,6 +2765,8 @@ int bpf_add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, u16
>> offset)
>>   	desc->func_model = func_model;
>>   	sort(tab->descs, tab->nr_descs, sizeof(tab->descs[0]),
>>   	     kfunc_desc_cmp_by_id_off, NULL);
>> +
>> +	env->prog->jit_required = 1;
> 
> That's ok, and I think Sashiko is right about this patch.
> 
>>   	return 0;
>>   }

As discussed in another thread, I will update bpf_prog_has_kfunc_call()
in v8, like this:

```
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 25aea4271cd0..c34cc524651a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2770,7 +2770,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env
*env, u32 func_id, u16 offset)

   bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
   {
-       return !!prog->aux->kfunc_tab;
+       return prog->aux->kfunc_tab && prog->aux->kfunc_tab->nr_descs;
   }

   static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
```

IIUC, there are two places to modify so far:
(1) struct bpf_prog
(2) bpf_prog_has_kfunc_call()

If you have any more comments, please let me know.

Thanks,
Tiezhu

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[KaFai Wan]

On Fri, 2026-07-03 at 23:53 +0800, Tiezhu Yang wrote:
> On 7/3/26 22:14, Leon Hwang wrote:
> > On 2026/7/3 14:59, Tiezhu Yang wrote:
> > [...]
> > > > > ```
> > > > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > > > > index f496b45b9da4..1f5824c1c691 100644
> > > > > --- a/kernel/bpf/verifier.c
> > > > > +++ b/kernel/bpf/verifier.c
> > > > > @@ -2772,7 +2772,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env
> > > > > *env, u32 func_id, u16 offset)
> > > > > 
> > > > >    bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
> > > > >    {
> > > > > -       return !!prog->aux->kfunc_tab;
> > > > > +       return prog->jit_required && !!prog->aux->kfunc_tab;
> > > > 
> > > > 
> > > > When 'prog->jit_required' is used for JIT-inlineable helper call, this
> > > > change could also cause false positive for the above pruned kfunc case.
> > > > 
> > > > If you don't want bpf_fixup_call_args() rejects the program with -EINVAL
> > > > for the pruned kfunc case, suggest moving 'if (!func_id && !offset)'
> > > > before the tab allocation in bpf_add_kfunc_call().
> > > 
> > > How about this:
> > > 
> > > ```
> > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > > index 25aea4271cd0..c34cc524651a 100644
> > > --- a/kernel/bpf/verifier.c
> > > +++ b/kernel/bpf/verifier.c
> > > @@ -2770,7 +2770,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env
> > > *env, u32 func_id, u16 offset)
> > > 
> > >   bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
> > >   {
> > > -       return !!prog->aux->kfunc_tab;
> > > +       return prog->aux->kfunc_tab && prog->aux->kfunc_tab->nr_descs > 0;
> > 
> > 
> > NIT: drop '> 0'
> > 
> > Looks better.
> 
> OK, will do it in v8.
> 
> > 
> > >   }
> > > 
> > >   static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
> > > ```
> > > IMO, there are no side effects for the following four cases:
> > > 
> > > 1. Pure JIT-inlined Helper
> > > 2. Pure Pruned kfunc
> > > 3. Pruned kfunc + Inlined Helper
> > > 4. Active (Unpruned) kfunc
> > > 
> > 
> > This change allows pruned kfunc + interpreter fallback and pruned kfunc
> > + bpf_fixup_call_args(), when CONFIG_BPF_JIT_ALWAYS_ON is off.
> > 
> > Does it look like a pre-existing issue?
> 
> I think so.

no, it's not. for kfunc insn, ->imm means btf_id and ->off leads to fd of btf file.
we replace ->imm to actual address and reject invalid kfunc in bpf_fixup_kfunc_call(). 

all pruned kfuncs allowed in bpf_add_kfunc_call() are rejected in bpf_fixup_kfunc_call(), before
call bpf_fixup_call_args(), no pruned kfuncs fall back to the interpreter.

I think we can set ->jit_required at the entry of bpf_add_kfunc_call() instead of end, make less
confusion of AI.

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d46f7db20d8f..4f7b43ab3729 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2713,6 +2713,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, u16 offset)
 			return -ENOMEM;
 		prog_aux->kfunc_tab = tab;
 	}
+	env->prog->jit_required = 1;
 
 	/* func_id == 0 is always invalid, but instead of returning an error, be
 	 * conservative and wait until the code elimination pass before returning

> 
> > 
> > Pls read "Support kernel module function calls from eBPF" [1] to
> > understand the background of introducing func_id=0 kfunc.
> > 
> > [1] https://lore.kernel.org/bpf/20211002011757.311265-1-memxor@gmail.com/
> > 
> > Thanks,
> > Leon
> 
> Thanks,
> Tiezhu
> 

-- 
Thanks,
KaFai

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[KaFai Wan]

On Sat, 2026-07-04 at 00:14 +0800, Tiezhu Yang wrote:
> On 7/3/26 21:55, KaFai Wan wrote:
> > On Thu, 2026-07-02 at 22:36 +0800, Tiezhu Yang wrote:
> > > Introduce a 'jit_required' bitfield flag at the end of the
> > > flags group in struct bpf_prog. This bit tracks whether a
> > > program strictly requires the JIT compiler.
> > > 
> > > Set this flag to 1 when a kfunc call is added at the end of
> > > bpf_add_kfunc_call().
> > > 
> > > In __bpf_prog_select_runtime(), check with fp->jit_required
> > > rather than bpf_prog_has_kfunc_call() to unify the logic.
> > > 
> > > Suggested-by: Alexei Starovoitov <ast@kernel.org>
> > > Suggested-by: KaFai Wan <kafai.wan@linux.dev>
> > > Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> > > ---
> > >   include/linux/bpf.h   | 3 ++-
> > >   kernel/bpf/core.c     | 3 +--
> > >   kernel/bpf/verifier.c | 2 ++
> > >   3 files changed, 5 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > > index ba09795e0bfd..4e2b059d71f3 100644
> > > --- a/include/linux/bpf.h
> > > +++ b/include/linux/bpf.h
> > > @@ -1880,7 +1880,8 @@ struct bpf_prog {
> > >   				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 */
> > > +				sleepable:1,	/* BPF program is sleepable */
> > > +				jit_required:1;	/* program strictly requires JIT
> > > compiler
> > > */
> > 
> > In v6 you're using 'u8 jit_required', I thought it would be 'u8 jit_required:1', so we use one
> > byte
> > and left 3 byte hole for future use.
> > 
> > This version left 2 bytes hole, same as v5, but it can easily be misleading because of the u16
> > type,
> > since we used 17 bits. I prefer v5, it has better readability.
> 
> OK, I will use the previous layout in v8, like this:
> 
> ```
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index ba09795e0bfd..463fae6a5c33 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1865,8 +1865,9 @@ struct bpf_prog_aux {
> 
>   struct bpf_prog {
>   	u16			pages;		/* Number of allocated pages */
> -	u16			jited:1,	/* Is our filter JIT'ed? */
> +	u32			jited:1,	/* Is our filter JIT'ed? */
>   				jit_requested:1,/* archs need to JIT the prog */
> +				jit_required:1, /* program strictly requires JIT compiler */
>   				gpl_compatible:1, /* Is filter GPL compatible? */
>   				cb_access:1,	/* Is control block accessed? */
>   				dst_needed:1,	/* Do we need dst entry? */
> ```
> 
> > 
> > >   	enum bpf_prog_type	type;		/* Type of BPF program */
> > >   	enum bpf_attach_type	expected_attach_type; /* For some prog types */
> > >   	u32			len;		/* Number of filter blocks */
> > > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> > > index 649cce41e13f..5fcd19ccb41a 100644
> > > --- a/kernel/bpf/core.c
> > > +++ b/kernel/bpf/core.c
> > > @@ -2619,8 +2619,7 @@ struct bpf_prog *__bpf_prog_select_runtime(struct bpf_verifier_env *env,
> > > struct
> > >   	if (fp->bpf_func)
> > >   		goto finalize;
> > >   
> > > -	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
> > > -	    bpf_prog_has_kfunc_call(fp))
> > > +	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || fp->jit_required)
> > >   		jit_needed = true;
> > >   
> > >   	if (!bpf_prog_select_interpreter(fp))
> > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > > index 25aea4271cd0..f496b45b9da4 100644
> > > --- a/kernel/bpf/verifier.c
> > > +++ b/kernel/bpf/verifier.c
> > > @@ -2765,6 +2765,8 @@ int bpf_add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, u16
> > > offset)
> > >   	desc->func_model = func_model;
> > >   	sort(tab->descs, tab->nr_descs, sizeof(tab->descs[0]),
> > >   	     kfunc_desc_cmp_by_id_off, NULL);
> > > +
> > > +	env->prog->jit_required = 1;
> > 
> > That's ok, and I think Sashiko is right about this patch.
> > 
> > >   	return 0;
> > >   }
> 
> As discussed in another thread, I will update bpf_prog_has_kfunc_call()
> in v8, like this:
> 
> ```
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 25aea4271cd0..c34cc524651a 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2770,7 +2770,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env
> *env, u32 func_id, u16 offset)
> 
>    bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
>    {
> -       return !!prog->aux->kfunc_tab;
> +       return prog->aux->kfunc_tab && prog->aux->kfunc_tab->nr_descs;
>    }
> 
>    static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
> ```
> 
> IIUC, there are two places to modify so far:
> (1) struct bpf_prog

yes

> (2) bpf_prog_has_kfunc_call()

I think we can remove this func.

actually, I feed your patch to dsv4-pro and gpt-5.4 yesterday, both point out the we should do this
and change the log message.

diff --git a/kernel/bpf/fixups.c b/kernel/bpf/fixups.c
index 12a8a4eb757f..7fb92b5fa415 100644
--- a/kernel/bpf/fixups.c
+++ b/kernel/bpf/fixups.c
@@ -1378,7 +1378,6 @@ int bpf_fixup_call_args(struct bpf_verifier_env *env)
 #ifndef CONFIG_BPF_JIT_ALWAYS_ON
 	struct bpf_prog *prog = env->prog;
 	struct bpf_insn *insn = prog->insnsi;
-	bool has_kfunc_call = bpf_prog_has_kfunc_call(prog);
 	int depth;
 #endif
 	int i, err = 0;
@@ -1404,7 +1403,7 @@ int bpf_fixup_call_args(struct bpf_verifier_env *env)
 			return err;
 	}
 #ifndef CONFIG_BPF_JIT_ALWAYS_ON
-	if (has_kfunc_call) {
+	if (prog->jit_required) {
 		verbose(env, "calling kernel functions are not allowed in non-JITed programs\n");
 		return -EINVAL;
 	}

I think we can change the log message for general purpose no just for kunc, so we can know why prog
failed in patch#2 as you test yesterday.

> 
> If you have any more comments, please let me know.
> 
> Thanks,
> Tiezhu
> 

-- 
Thanks,
KaFai

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[KaFai Wan]

On Sat, 2026-07-04 at 00:14 +0800, Tiezhu Yang wrote:
> On 7/3/26 21:55, KaFai Wan wrote:
> > On Thu, 2026-07-02 at 22:36 +0800, Tiezhu Yang wrote:
> > > Introduce a 'jit_required' bitfield flag at the end of the
> > > flags group in struct bpf_prog. This bit tracks whether a
> > > program strictly requires the JIT compiler.
> > > 
> > > Set this flag to 1 when a kfunc call is added at the end of
> > > bpf_add_kfunc_call().
> > > 
> > > In __bpf_prog_select_runtime(), check with fp->jit_required
> > > rather than bpf_prog_has_kfunc_call() to unify the logic.
> > > 
> > > Suggested-by: Alexei Starovoitov <ast@kernel.org>
> > > Suggested-by: KaFai Wan <kafai.wan@linux.dev>
> > > Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> > > ---
> > >   include/linux/bpf.h   | 3 ++-
> > >   kernel/bpf/core.c     | 3 +--
> > >   kernel/bpf/verifier.c | 2 ++
> > >   3 files changed, 5 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > > index ba09795e0bfd..4e2b059d71f3 100644
> > > --- a/include/linux/bpf.h
> > > +++ b/include/linux/bpf.h
> > > @@ -1880,7 +1880,8 @@ struct bpf_prog {
> > >   				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 */
> > > +				sleepable:1,	/* BPF program is sleepable */
> > > +				jit_required:1;	/* program strictly requires JIT
> > > compiler
> > > */
> > 
> > In v6 you're using 'u8 jit_required', I thought it would be 'u8 jit_required:1', so we use one
> > byte
> > and left 3 byte hole for future use.
> > 
> > This version left 2 bytes hole, same as v5, but it can easily be misleading because of the u16
> > type,
> > since we used 17 bits. I prefer v5, it has better readability.
> 
> OK, I will use the previous layout in v8, like this:
> 
> ```
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index ba09795e0bfd..463fae6a5c33 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1865,8 +1865,9 @@ struct bpf_prog_aux {
> 
>   struct bpf_prog {
>   	u16			pages;		/* Number of allocated pages */
> -	u16			jited:1,	/* Is our filter JIT'ed? */
> +	u32			jited:1,	/* Is our filter JIT'ed? */
>   				jit_requested:1,/* archs need to JIT the prog */
> +				jit_required:1, /* program strictly requires JIT compiler */
>   				gpl_compatible:1, /* Is filter GPL compatible? */
>   				cb_access:1,	/* Is control block accessed? */
>   				dst_needed:1,	/* Do we need dst entry? */
> ```
> 
> > 
> > >   	enum bpf_prog_type	type;		/* Type of BPF program */
> > >   	enum bpf_attach_type	expected_attach_type; /* For some prog types */
> > >   	u32			len;		/* Number of filter blocks */
> > > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> > > index 649cce41e13f..5fcd19ccb41a 100644
> > > --- a/kernel/bpf/core.c
> > > +++ b/kernel/bpf/core.c
> > > @@ -2619,8 +2619,7 @@ struct bpf_prog *__bpf_prog_select_runtime(struct bpf_verifier_env *env,
> > > struct
> > >   	if (fp->bpf_func)
> > >   		goto finalize;
> > >   
> > > -	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
> > > -	    bpf_prog_has_kfunc_call(fp))
> > > +	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || fp->jit_required)
> > >   		jit_needed = true;
> > >   
> > >   	if (!bpf_prog_select_interpreter(fp))
> > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > > index 25aea4271cd0..f496b45b9da4 100644
> > > --- a/kernel/bpf/verifier.c
> > > +++ b/kernel/bpf/verifier.c
> > > @@ -2765,6 +2765,8 @@ int bpf_add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, u16
> > > offset)
> > >   	desc->func_model = func_model;
> > >   	sort(tab->descs, tab->nr_descs, sizeof(tab->descs[0]),
> > >   	     kfunc_desc_cmp_by_id_off, NULL);
> > > +
> > > +	env->prog->jit_required = 1;
> > 
> > That's ok, and I think Sashiko is right about this patch.
> > 
> > >   	return 0;
> > >   }
> 
> As discussed in another thread, I will update bpf_prog_has_kfunc_call()
> in v8, like this:
> 
> ```
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 25aea4271cd0..c34cc524651a 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2770,7 +2770,7 @@ int bpf_add_kfunc_call(struct bpf_verifier_env
> *env, u32 func_id, u16 offset)
> 
>    bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
>    {
> -       return !!prog->aux->kfunc_tab;
> +       return prog->aux->kfunc_tab && prog->aux->kfunc_tab->nr_descs;

!!prog->aux->kfunc_tab works fine when bpf_prog_has_kfunc_call() called currently, no need to check 
prog->aux->kfunc_tab->nr_descs, see other thread.

>    }
> 
>    static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
> ```
> 
> IIUC, there are two places to modify so far:
> (1) struct bpf_prog
> (2) bpf_prog_has_kfunc_call()
> 
> If you have any more comments, please let me know.
> 
> Thanks,
> Tiezhu
> 

-- 
Thanks,
KaFai

Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[KaFai Wan]

On Fri, 2026-07-03 at 23:56 +0800, Tiezhu Yang wrote:
> On 7/3/26 21:51, KaFai Wan wrote:
> > 
> > Was it tested after compiling together with patch #2? seems patch #2 works.
> 
> Yes.
> 
> > 
works as expected.

-- 
Thanks,
KaFai