linux-kernel - Re: [PATCH v11 2/9] btf: Handle dynamic pointer parameter in kfuncs

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Message-ID: <43277fc1-f03e-38a0-0d07-64892a67ac1d@iogearbox.net>
Date:   Mon, 15 Aug 2022 18:45:59 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Roberto Sassu <roberto.sassu@...wei.com>, ast@...nel.org,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org,
        sdf@...gle.com, haoluo@...gle.com, jolsa@...nel.org,
        mykolal@...com, corbet@....net, dhowells@...hat.com,
        jarkko@...nel.org, rostedt@...dmis.org, mingo@...hat.com,
        paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com,
        shuah@...nel.org
Cc:     bpf@...r.kernel.org, linux-doc@...r.kernel.org,
        keyrings@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        Joanne Koong <joannelkoong@...il.com>
Subject: Re: [PATCH v11 2/9] btf: Handle dynamic pointer parameter in kfuncs

On 8/12/22 12:18 PM, Roberto Sassu wrote:
> Allow the bpf_dynptr_kern parameter to be specified in kfuncs. Also, ensure
> that the dynamic pointer is valid and initialized.
> 
> Cc: Joanne Koong <joannelkoong@...il.com>
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> ---
>   include/linux/bpf_verifier.h |  3 +++
>   kernel/bpf/btf.c             | 22 ++++++++++++++++++++++
>   kernel/bpf/verifier.c        |  4 ++--
>   3 files changed, 27 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index 2e3bad8640dc..55876fbdbae2 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -560,6 +560,9 @@ int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state
>   			     u32 regno);
>   int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
>   		   u32 regno, u32 mem_size);
> +bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,
> +			      struct bpf_reg_state *reg,
> +			      enum bpf_arg_type arg_type);
>   
>   /* this lives here instead of in bpf.h because it needs to dereference tgt_prog */
>   static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog,
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index e49b3b6d48ad..86e63f2ee5da 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -195,6 +195,10 @@
>   	     i < btf_type_vlen(struct_type);					\
>   	     i++, member++)
>   
> +#define stringify_struct(x)			\
> +	({ BUILD_BUG_ON(sizeof(struct x) < 0);	\
> +	   __stringify(x); })
> +

I'd say lets move this to include/linux/btf.h with a comment explaining the BUILD_BUG_ON()
which ensures the struct actually exits.

If there's ever use outside of BTF, it could be relocated to include/linux/stringify.h.

>   DEFINE_IDR(btf_idr);
>   DEFINE_SPINLOCK(btf_idr_lock);
>