netdev - Re: [PATCH bpf-next 4/7] libbpf: sanitize BPF program code for bpf_probe_read_{kernel,user}[

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Date:   Tue, 18 Aug 2020 18:42:22 -0700
From:   Yonghong Song <yhs@...com>
To:     Andrii Nakryiko <andriin@...com>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>, <ast@...com>, <daniel@...earbox.net>
CC:     <andrii.nakryiko@...il.com>, <kernel-team@...com>
Subject: Re: [PATCH bpf-next 4/7] libbpf: sanitize BPF program code for
 bpf_probe_read_{kernel,user}[_str]



On 8/18/20 2:33 PM, Andrii Nakryiko wrote:
> Add BPF program code sanitization pass, replacing calls to BPF
> bpf_probe_read_{kernel,user}[_str]() helpers with bpf_probe_read[_str](), if
> libbpf detects that kernel doesn't support new variants.

I know this has been merged. The whole patch set looks good to me.
A few nit or questions below.

> 
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
>   tools/lib/bpf/libbpf.c | 80 ++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 80 insertions(+)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index ab0c3a409eea..bdc08f89a5c0 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -180,6 +180,8 @@ enum kern_feature_id {
>   	FEAT_ARRAY_MMAP,
>   	/* kernel support for expected_attach_type in BPF_PROG_LOAD */
>   	FEAT_EXP_ATTACH_TYPE,
> +	/* bpf_probe_read_{kernel,user}[_str] helpers */
> +	FEAT_PROBE_READ_KERN,
>   	__FEAT_CNT,
>   };
>   
> @@ -3591,6 +3593,27 @@ static int probe_kern_exp_attach_type(void)
>   	return probe_fd(bpf_load_program_xattr(&attr, NULL, 0));
>   }
>   
[...]
>   
> +static bool insn_is_helper_call(struct bpf_insn *insn, enum bpf_func_id *func_id)
> +{
> +	__u8 class = BPF_CLASS(insn->code);
> +
> +	if ((class == BPF_JMP || class == BPF_JMP32) &&

Do we support BPF_JMP32 + BPF_CALL ... as a helper call?
I am not aware of this.

> +	    BPF_OP(insn->code) == BPF_CALL &&
> +	    BPF_SRC(insn->code) == BPF_K &&
> +	    insn->src_reg == 0 && insn->dst_reg == 0) {
> +		    if (func_id)
> +			    *func_id = insn->imm;

looks like func_id is always non-NULL. Unless this is to support future 
usage where func_id may be NULL, the above condition probably not needed.

> +		    return true;
> +	}
> +	return false;
> +}
> +
[...]