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

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Message-ID: <qesoniwddyi2qrjxavxlfvmy5lq6fmenrp5zvz347dnknuf7yb@wi3agqebvgqm>
Date: Mon, 14 Apr 2025 22:28:20 -0600
From: Daniel Xu <dxu@...uu.xyz>
To: Stanislav Fomichev <stfomichev@...il.com>
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 Wed, Apr 09, 2025 at 07:25:14AM -0700, Stanislav Fomichev wrote:
> 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

Ah didn't know about this. Makes sense - will do.

Thanks,
Daniel