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Message-ID: <2543b57d-d7a2-19a0-e532-0d5e3b04a45e@huawei.com>
Date:   Wed, 7 Dec 2022 16:49:36 +0800
From:   Yang Jihong <yangjihong1@...wei.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Yonghong Song <yhs@...a.com>, <bjorn@...nel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Shubham Bansal <illusionist.neo@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        <colin.i.king@...il.com>, Artem Savkov <asavkov@...hat.com>,
        Delyan Kratunov <delyank@...com>, bpf <bpf@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 1/4] bpf: Adapt 32-bit return value kfunc for
 32-bit ARM when zext extension

Hello,

On 2022/12/5 9:19, Yang Jihong wrote:
> 
> 
> On 2022/12/4 0:40, Alexei Starovoitov wrote:
>> On Fri, Dec 2, 2022 at 6:58 PM Yang Jihong <yangjihong1@...wei.com> 
>> wrote:
>>>
>>>
>>>
>>> On 2022/11/29 0:41, Alexei Starovoitov wrote:
>>>> On Mon, Nov 28, 2022 at 4:40 AM Yang Jihong <yangjihong1@...wei.com> 
>>>> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 2022/11/28 9:57, Alexei Starovoitov wrote:
>>>>>> On Sat, Nov 26, 2022 at 05:45:27PM +0800, 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 | 44 
>>>>>>> ++++++++++++++++++++++++++++++++++++++++---
>>>>>>>     1 file changed, 41 insertions(+), 3 deletions(-)
>>>>>>>
>>>>>>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>>>>>>> index 264b3dc714cc..193ea927aa69 100644
>>>>>>> --- a/kernel/bpf/verifier.c
>>>>>>> +++ b/kernel/bpf/verifier.c
>>>>>>> @@ -1927,6 +1927,21 @@ find_kfunc_desc(const struct bpf_prog 
>>>>>>> *prog, u32 func_id, u16 offset)
>>>>>>>                       sizeof(tab->descs[0]), 
>>>>>>> kfunc_desc_cmp_by_id_off);
>>>>>>>     }
>>>>>>>
>>>>>>> +static int kfunc_desc_cmp_by_imm(const void *a, const void *b);
>>>>>>> +
>>>>>>> +static const struct bpf_kfunc_desc *
>>>>>>> +find_kfunc_desc_by_imm(const struct bpf_prog *prog, s32 imm)
>>>>>>> +{
>>>>>>> +    struct bpf_kfunc_desc desc = {
>>>>>>> +            .imm = imm,
>>>>>>> +    };
>>>>>>> +    struct bpf_kfunc_desc_tab *tab;
>>>>>>> +
>>>>>>> +    tab = prog->aux->kfunc_tab;
>>>>>>> +    return bsearch(&desc, tab->descs, tab->nr_descs,
>>>>>>> +                   sizeof(tab->descs[0]), kfunc_desc_cmp_by_imm);
>>>>>>> +}
>>>>>>> +
>>>>>>>     static struct btf *__find_kfunc_desc_btf(struct 
>>>>>>> bpf_verifier_env *env,
>>>>>>>                                         s16 offset)
>>>>>>>     {
>>>>>>> @@ -2342,6 +2357,13 @@ static bool is_reg64(struct 
>>>>>>> bpf_verifier_env *env, struct bpf_insn *insn,
>>>>>>>                         */
>>>>>>>                        if (insn->src_reg == BPF_PSEUDO_CALL)
>>>>>>>                                return false;
>>>>>>> +
>>>>>>> +                    /* Kfunc call will reach here because of 
>>>>>>> insn_has_def32,
>>>>>>> +                     * conservatively return TRUE.
>>>>>>> +                     */
>>>>>>> +                    if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL)
>>>>>>> +                            return true;
>>>>>>> +
>>>>>>>                        /* Helper call will reach here because of 
>>>>>>> arg type
>>>>>>>                         * check, conservatively return TRUE.
>>>>>>>                         */
>>>>>>> @@ -2405,10 +2427,26 @@ static bool is_reg64(struct 
>>>>>>> bpf_verifier_env *env, struct bpf_insn *insn,
>>>>>>>     }
>>>>>>>
>>>>>>>     /* Return the regno defined by the insn, or -1. */
>>>>>>> -static int insn_def_regno(const struct bpf_insn *insn)
>>>>>>> +static int insn_def_regno(struct bpf_verifier_env *env, const 
>>>>>>> struct bpf_insn *insn)
>>>>>>>     {
>>>>>>>        switch (BPF_CLASS(insn->code)) {
>>>>>>>        case BPF_JMP:
>>>>>>> +            if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {
>>>>>>> +                    const struct bpf_kfunc_desc *desc;
>>>>>>> +
>>>>>>> +                    /* The value of desc cannot be NULL */
>>>>>>> +                    desc = find_kfunc_desc_by_imm(env->prog, 
>>>>>>> insn->imm);
>>>>>>> +
>>>>>>> +                    /* A kfunc can return void.
>>>>>>> +                     * The btf type of the kfunc's return value 
>>>>>>> needs
>>>>>>> +                     * to be checked against "void" first
>>>>>>> +                     */
>>>>>>> +                    if (desc->func_model.ret_size == 0)
>>>>>>> +                            return -1;
>>>>>>> +                    else
>>>>>>> +                            return insn->dst_reg;
>>>>>>> +            }
>>>>>>> +            fallthrough;
>>>>>>
>>>>>> I cannot make any sense of this patch.
>>>>>> insn->dst_reg above is 0.
>>>>>> The kfunc call doesn't define a register from insn_def_regno() pov.
>>>>>>
>>>>>> Are you hacking insn_def_regno() to return 0 so that
>>>>>> if (WARN_ON(load_reg == -1)) {
>>>>>>      verbose(env, "verifier bug. zext_dst is set, but no reg is 
>>>>>> defined\n");
>>>>>>      return -EFAULT;
>>>>>> }
>>>>>> in opt_subreg_zext_lo32_rnd_hi32() doesn't trigger ?
>>>>>>
>>>>>> But this verifier message should have been a hint that you need
>>>>>> to analyze why zext_dst is set on this kfunc call.
>>>>>> Maybe it shouldn't ?
>>>>>> Did you analyze the logic of mark_btf_func_reg_size() ?
>>>>> make r0 zext is not caused by mark_btf_func_reg_size.
>>>>>
>>>>> This problem occurs when running the kfunc_call_test_ref_btf_id test
>>>>> case in the 32-bit ARM environment.
>>>>
>>>> Why is it not failing on x86-32 ?
>>> Use the latest mainline kernel code to test on the x86_32 machine. The
>>> test also fails:
>>>
>>>     # ./test_progs -t kfunc_call/kfunc_call_test_ref_btf_id
>>>     Failed to load bpf_testmod.ko into the kernel: -8
>>>     WARNING! Selftests relying on bpf_testmod.ko will be skipped.
>>>     libbpf: prog 'kfunc_call_test_ref_btf_id': BPF program load failed:
>>> Bad address
>>>     libbpf: prog 'kfunc_call_test_ref_btf_id': -- BEGIN PROG LOAD LOG --
>>>     processed 25 insns (limit 1000000) max_states_per_insn 0 
>>> total_states
>>> 2 peak_states 2 mark_read 1
>>>     -- END PROG LOAD LOG --
>>>     libbpf: prog 'kfunc_call_test_ref_btf_id': failed to load: -14
>>>     libbpf: failed to load object 'kfunc_call_test'
>>>     libbpf: failed to load BPF skeleton 'kfunc_call_test': -14
>>>     verify_success:FAIL:skel unexpected error: -14
>>>
>>> Therefore, this problem also exists on x86_32:
>>> "verifier bug. zext_dst is set, but no reg is defined"
>>
>> The kernel returns -14 == EFAULT.
>> That's a completely different issue.
> It's the same problem. The opt_subreg_zext_lo32_rnd_hi32 function fails 
> to check here and returns -EFAULT
> 
> opt_subreg_zext_lo32_rnd_hi32 {
>    ...
>     if (WARN_ON(load_reg == -1)) {
>             verbose(env, "verifier bug. zext_dst is set, but no reg is 
> defined\n");
>             return -EFAULT;
>     }
>    ...
> }
>> .
I see that there are emails from the community talking about the same 
problem, and come up with a solution:
https://lore.kernel.org/bpf/20221202103620.1915679-1-bjorn@kernel.org/T/

will remove this patch based on that patch.

Thanks,
Yang
>>
> 
> .

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