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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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