netdev - Re: [PATCH bpf v2 1/5] bpf: Adapt 32-bit return value kfunc for 32-bit ARM when zext extension

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Date:   Sat, 26 Nov 2022 17:45:57 +0800
From:   Yang Jihong <yangjihong1@...wei.com>
To:     Martin KaFai Lau <martin.lau@...ux.dev>
CC:     <ast@...nel.org>, <daniel@...earbox.net>, <andrii@...nel.org>,
        <song@...nel.org>, <yhs@...com>, <john.fastabend@...il.com>,
        <kpsingh@...nel.org>, <sdf@...gle.com>, <haoluo@...gle.com>,
        <jolsa@...nel.org>, <illusionist.neo@...il.com>,
        <linux@...linux.org.uk>, <davem@...emloft.net>,
        <edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
        <mykolal@...com>, <shuah@...nel.org>,
        <benjamin.tissoires@...hat.com>, <memxor@...il.com>,
        <asavkov@...hat.com>, <delyank@...com>, <bpf@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf v2 1/5] bpf: Adapt 32-bit return value kfunc for
 32-bit ARM when zext extension

Hello,

On 2022/11/9 7:12, Martin KaFai Lau wrote:
> On 11/7/22 1:20 AM, Yang Jihong wrote:
>> For ARM32 architecture, if data width of kfunc return value is 32 bits,
>> need to do explicit zero extension for high 32-bit, insn_def_regno should
>> return dst_reg for BPF_JMP type of BPF_PSEUDO_KFUNC_CALL. Otherwise,
>> opt_subreg_zext_lo32_rnd_hi32 returns -EFAULT, resulting in BPF failure.
>>
>> Signed-off-by: Yang Jihong <yangjihong1@...wei.com>
>> ---
>>   kernel/bpf/verifier.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index 7f0a9f6cb889..bac37757ffca 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -2404,6 +2404,9 @@ static int insn_def_regno(const struct bpf_insn 
>> *insn)
>>   {
>>       switch (BPF_CLASS(insn->code)) {
>>       case BPF_JMP:
>> +        if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL)
>> +            return insn->dst_reg;
> 
> This does not look right.  A kfunc can return void.  The btf type of the 
> kfunc's return value needs to be checked against "void" first?
OK, will add the check in next version.

> Also, this will affect insn_has_def32(), does is_reg64 (called from 
> insn_has_def32) need to be adjusted also?
Yes, is_reg64 need to be adjusted, will fix in next version.
> 
> 
> For patch 2, as replied earlier in v1, I would separate out the prog 
> that does __sk_buff->sk and use the uapi's bpf.h instead of vmlinux.h 
> since it does not need CO-RE.
OK, will remove adjust sk check patches in next verion.

As mentioned in v1:
"bpf-tc program can take'struct sk_buff *skb' instead of'struct
__sk_buff *skb' but it will be a separate topic."

It is a separate topic, only the lskel test cases are affected.
The ARM32 kfunc function is not affected.

> 
> This set should target for bpf-next instead of bpf.
OK, will send to bpf-next in next version.

Thanks,
Yang