linux-kernel - Re: [RFC bpf-next 10/13] bpf: verifier: Add indirection to kallsyms_lookup

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Message-ID: <Z_aDSipnuvNAhHbE@mini-arch>
Date: Wed, 9 Apr 2025 07:25:14 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Daniel Xu <dxu@...uu.xyz>
Cc: andrii@...nel.org, ast@...nel.org, daniel@...earbox.net,
	john.fastabend@...il.com, martin.lau@...ux.dev, eddyz87@...il.com,
	song@...nel.org, yonghong.song@...ux.dev, kpsingh@...nel.org,
	sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org,
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC bpf-next 10/13] bpf: verifier: Add indirection to
 kallsyms_lookup_name()

On 04/08, Daniel Xu wrote:
> kallsyms_lookup_name() cannot be exported from the kernel for policy
> reasons, so add this layer of indirection to allow the verifier to still
> do kfunc and global variable relocations.
> 
> Signed-off-by: Daniel Xu <dxu@...uu.xyz>
> ---
>  include/linux/bpf.h   |  2 ++
>  kernel/bpf/core.c     | 14 ++++++++++++++
>  kernel/bpf/verifier.c | 13 +++++--------
>  3 files changed, 21 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 44133727820d..a5806a7b31d3 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2797,6 +2797,8 @@ static inline int kfunc_desc_cmp_by_id_off(const void *a, const void *b)
>  }
>  const struct bpf_kfunc_desc *
>  find_kfunc_desc(const struct bpf_prog *prog, u32 func_id, u16 offset);
> +unsigned long bpf_lookup_type_addr(struct btf *btf, const struct btf_type *func,
> +				   const char **name);
>  int bpf_get_kfunc_addr(const struct bpf_prog *prog, u32 func_id,
>  		       u16 btf_fd_idx, u8 **func_addr);
>  
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index e892e469061e..13301a668fe0 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -1639,6 +1639,20 @@ find_kfunc_desc(const struct bpf_prog *prog, u32 func_id, u16 offset)
>  }
>  EXPORT_SYMBOL_GPL(find_kfunc_desc);
>  
> +unsigned long bpf_lookup_type_addr(struct btf *btf, const struct btf_type *t,
> +				   const char **name)
> +{
> +	unsigned long addr;
> +
> +	*name = btf_name_by_offset(btf, t->name_off);
> +	addr = kallsyms_lookup_name(*name);
> +	if (!addr)
> +		return -ENOENT;
> +
> +	return addr;
> +}
> +EXPORT_SYMBOL_GPL(bpf_lookup_type_addr);

Let's namespecify all these new exports? EXPORT_SYMBOL_NS_GPL