linux-kernel - Re: [PATCH] bpf: replace kvfree with kfree for kzalloc memory

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Message-ID: <6b72f32a9d1b137fb3f3ae0c439b1688fef8dd8d.camel@gmail.com>
Date: Mon, 11 Aug 2025 09:46:33 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Qianfeng Rong <rongqianfeng@...o.com>, Alexei Starovoitov
 <ast@...nel.org>,  Daniel Borkmann <daniel@...earbox.net>, John Fastabend
 <john.fastabend@...il.com>, Andrii Nakryiko	 <andrii@...nel.org>, Martin
 KaFai Lau <martin.lau@...ux.dev>, Song Liu	 <song@...nel.org>, Yonghong
 Song <yonghong.song@...ux.dev>, KP Singh	 <kpsingh@...nel.org>, Stanislav
 Fomichev <sdf@...ichev.me>, Hao Luo	 <haoluo@...gle.com>, Jiri Olsa
 <jolsa@...nel.org>, bpf@...r.kernel.org, 	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bpf: replace kvfree with kfree for kzalloc memory

On Mon, 2025-08-11 at 20:39 +0800, Qianfeng Rong wrote:
> The 'backedge' pointer is allocated with kzalloc(), which returns
> physically contiguous memory. Using kvfree() to deallocate such
> memory is functionally safe but semantically incorrect.
> 
> Replace kvfree() with kfree() to avoid unnecessary is_vmalloc_addr()
> check in kvfree().
> 
> Signed-off-by: Qianfeng Rong <rongqianfeng@...o.com>
> ---

Acked-by: Eduard Zingerman <eddyz87@...il.com>

>  kernel/bpf/verifier.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index c4f69a9e9af6..4e5de1ff7e30 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -19553,7 +19553,7 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
>  				err = err ?: add_scc_backedge(env, &sl->state, backedge);
>  				if (err) {
>  					free_verifier_state(&backedge->state, false);
> -					kvfree(backedge);
> +					kfree(backedge);

The backedge encapsulates verifier state, verifier states are
allocated using kzalloc() and freed using kfreed() in other places in
verifier.c => I think this patch is valid.

>  					return err;
>  				}
>  			}