linux-kernel - Re: [PATCH bpf] selftests/bpf: Add a copyright notice to lpm_trie_map_get_next

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <8d61d6ab-b6c4-9e7b-45f2-f0a4972f04ce@huaweicloud.com>
Date: Tue, 5 Nov 2024 14:21:53 +0800
From: Hou Tao <houtao@...weicloud.com>
To: Ilya Leoshkevich <iii@...ux.ibm.com>,
 Byeonguk Jeong <jungbu2855@...il.com>
Cc: andrii@...nel.org, daniel@...earbox.net, martin.lau@...ux.dev,
 Alexei Starovoitov <ast@...nel.org>, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf] selftests/bpf: Add a copyright notice to
 lpm_trie_map_get_next_key

Hi,

On 11/5/2024 10:34 AM, Hou Tao wrote:
> Hi Ilya,
>
> On 11/4/2024 6:07 PM, Ilya Leoshkevich wrote:
>> On Mon, 2024-11-04 at 09:34 +0800, Hou Tao wrote:
>>> Hi,
>>>
>>> On 11/3/2024 2:04 PM, Byeonguk Jeong wrote:
>>>> Hi,
>>>>
>>>> The selftest "verifier_bits_iter/bad words" has been failed with
>>>> retval 115, while I did not touched anything but a comment.
>>>>
>>>> Do you have any idea why it failed? I am not sure whether it
>>>> indicates
>>>> any bugs in the kernel.
>>>>
>>>> Best,
>>>> Byeonguk
>>> Sorry for the inconvenience. It seems the test case
>>> "verifier_bits_iter/bad words" is flaky. It may fail randomly, such
>>> as
>>> in [1]. I think calling bpf_probe_read_kernel_common() on 3GB addr
>>> under
>>> s390 host may succeed and the content of the memory address will
>>> decide
>>> whether the test case will succeed or not. Do not know the reason why
>>> reading 3GB address succeeds under s390. Hope to get some insight
>>> from
>>> Ilya.  I think we could fix the failure first by using NULL as the
>>> address of bad words just like null_pointer test case does. Will
>>> merge
>>> the test in bad_words into the null_pointer case.
>> Hi,
>>
>> s390 kernel runs in a completely separate address space, there is no
>> user/kernel split at TASK_SIZE. The same address may be valid in both
>> the kernel and the user address spaces, there is no way to tell by
>> looking at it. The config option related to this property is
>> ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE.
>>
>> Also, unfortunately, 0 is a valid address in the s390 kernel address
>> space.
> Thanks for the detailed explanation. It seems both arm and x86 have
> select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE.
>> I wonder if we could use -4095 as an address that cannot be
>> dereferenced on all platforms?
> I have tested it in both arm64 and x86-64 that reading from -4095 by
> using copy_from_kernel_nofault() will return -EFAULT . For s390, I hope
> the bpf CI could help to test it. Will post a fix patch later.

On s390 host, it seems that using copy_from_kernel_nofault() to read
from -4095 returns -EFAULT as well [1], so the suggestion works. Thanks
again for the suggestion.

[1]
https://github.com/kernel-patches/bpf/actions/runs/11677589805/job/32515868794
>> Best regards,
>> Ilya
>
> .