linux-kernel - Re: [PATCH bpf-next v2 1/4] bpf: crypto: Use the correct destructor kfunc type

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Message-ID: <932a6a4d-d30b-4b85-b6a9-2eabeb5eaf2e@linux.dev>
Date: Fri, 25 Jul 2025 16:11:27 -0700
From: Yonghong Song <yonghong.song@...ux.dev>
To: Sami Tolvanen <samitolvanen@...gle.com>, bpf@...r.kernel.org
Cc: Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, John Fastabend <john.fastabend@...il.com>,
 KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
 Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
 Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>,
 Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 1/4] bpf: crypto: Use the correct destructor
 kfunc type



On 7/25/25 2:44 PM, Sami Tolvanen wrote:
> With CONFIG_CFI_CLANG enabled, the kernel strictly enforces that
> indirect function calls use a function pointer type that matches the
> target function. I ran into the following type mismatch when running
> BPF self-tests:
>
>    CFI failure at bpf_obj_free_fields+0x190/0x238 (target:
>      bpf_crypto_ctx_release+0x0/0x94; expected type: 0xa488ebfc)
>    Internal error: Oops - CFI: 00000000f2008228 [#1]  SMP
>    ...
>
> As bpf_crypto_ctx_release() is also used in BPF programs and using
> a void pointer as the argument would make the verifier unhappy, add
> a simple stub function with the correct type and register it as the
> destructor kfunc instead.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> ---
>   kernel/bpf/crypto.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/crypto.c b/kernel/bpf/crypto.c
> index 94854cd9c4cc..f44aa454826b 100644
> --- a/kernel/bpf/crypto.c
> +++ b/kernel/bpf/crypto.c
> @@ -261,6 +261,13 @@ __bpf_kfunc void bpf_crypto_ctx_release(struct bpf_crypto_ctx *ctx)
>   		call_rcu(&ctx->rcu, crypto_free_cb);
>   }
>   
> +__used __retain void __bpf_crypto_ctx_release(void *ctx)
> +{
> +	bpf_crypto_ctx_release(ctx);
> +}
> +
> +CFI_NOSEAL(__bpf_crypto_ctx_release);

Okay, looks like Peter has made similar changes before.
See https://lore.kernel.org/all/20231215092707.799451071@infradead.org/

To be consistent with existing code base, I think the following
change is better:

diff --git a/kernel/bpf/crypto.c b/kernel/bpf/crypto.c
index 94854cd9c4cc..a267d9087d40 100644
--- a/kernel/bpf/crypto.c
+++ b/kernel/bpf/crypto.c
@@ -261,6 +261,12 @@ __bpf_kfunc void bpf_crypto_ctx_release(struct bpf_crypto_ctx *ctx)
                 call_rcu(&ctx->rcu, crypto_free_cb);
  }
  
+__bpf_kfunc void bpf_crypto_ctx_release_dtor(void *ctx)
+{
+       bpf_crypto_ctx_release(ctx);
+}
+CFI_NOSEAL(bpf_crypto_ctx_release_dtor);
+
  static int bpf_crypto_crypt(const struct bpf_crypto_ctx *ctx,
                             const struct bpf_dynptr_kern *src,
                             const struct bpf_dynptr_kern *dst,
@@ -368,7 +374,7 @@ static const struct btf_kfunc_id_set crypt_kfunc_set = {
  
  BTF_ID_LIST(bpf_crypto_dtor_ids)
  BTF_ID(struct, bpf_crypto_ctx)
-BTF_ID(func, bpf_crypto_ctx_release)
+BTF_ID(func, bpf_crypto_ctx_release_dtor)
  
  static int __init crypto_kfunc_init(void)
  {

The same code pattern can be done for patch 2 and patch 3.

> +
>   static int bpf_crypto_crypt(const struct bpf_crypto_ctx *ctx,
>   			    const struct bpf_dynptr_kern *src,
>   			    const struct bpf_dynptr_kern *dst,
> @@ -368,7 +375,7 @@ static const struct btf_kfunc_id_set crypt_kfunc_set = {
>   
>   BTF_ID_LIST(bpf_crypto_dtor_ids)
>   BTF_ID(struct, bpf_crypto_ctx)
> -BTF_ID(func, bpf_crypto_ctx_release)
> +BTF_ID(func, __bpf_crypto_ctx_release)
>   
>   static int __init crypto_kfunc_init(void)
>   {