linux-kernel - Re: [PATCH bpf] selftests/bpf: DENYLIST.aarch64: Remove fexit

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Message-ID: <e35b2a2b-aa5e-b107-1fb9-927e43e06d88@iogearbox.net>
Date: Fri, 12 Jul 2024 18:19:29 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Puranjay Mohan <puranjay@...nel.org>, Manu Bretelle <chantra@...a.com>,
 KP Singh <kpsingh@...nel.org>, Andrii Nakryiko <andrii@...nel.org>,
 Eduard Zingerman <eddyz87@...il.com>, Mykola Lysenko <mykolal@...a.com>,
 Alexei Starovoitov <ast@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>,
 Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>,
 "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
 "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Florent Revest <revest@...gle.com>
Subject: Re: [PATCH bpf] selftests/bpf: DENYLIST.aarch64: Remove fexit_sleep

On 7/12/24 6:07 PM, Alexei Starovoitov wrote:
> On Fri, Jul 12, 2024 at 6:50 AM Daniel Borkmann <daniel@...earbox.net> wrote:
>> On 7/11/24 4:00 PM, Puranjay Mohan wrote:
>> [...]
>>> I was able find the root cause of this bug and will send a fix soon!
>>>
>>>> Unable to handle kernel paging request at virtual address ffff0000c2a80e68
>>>
>>> We are running this test on Qemu with '-cpu max', this means 52-bit
>>> virtual addresses are being used.
>>>
>>> The trampolines generation code has the following two lines:
>>>
>>>                emit_addr_mov_i64(A64_R(0), (const u64)im, ctx);
>>>                emit_call((const u64)__bpf_tramp_enter, ctx);
>>>
>>> here the address of struct bpf_tramp_image is moved to R0 and passed as
>>> an argument to __bpf_tramp_enter().
>>>
>>> emit_addr_mov_i64() assumes that the address passed to it is in the
>>> vmalloc space and uses at most 48 bits. It sets all the remaining bits
>>> to 1.
>>>
>>> but struct bpf_tramp_image is allocated using kzalloc() and when 52-bit
>>> VAs are used, its address is not guaranteed to be 48-bit, therefore we
>>> see this bug, where  0xfff[0]0000c2a80e68 is converted to
>>> 0xfff[f]0000c2a80e68 when the trampoline is generated.
>>>
>>> The fix would be use emit_a64_mov_i64() for moving this address into R0.
>>
>> It looks like there is still an issue left. A recent CI run on bpf-next is
>> still hitting the same on arm64:
>>
>> Base:
>>
>>     https://github.com/kernel-patches/bpf/commits/series/870746%3D%3Ebpf-next/
>>
>> CI:
>>
>>     https://github.com/kernel-patches/bpf/actions/runs/9905842936/job/27366435436
>>
>>     [...]
>>     #89/11   fexit_bpf2bpf/func_replace_global_func:OK
>>     #89/12   fexit_bpf2bpf/fentry_to_cgroup_bpf:OK
>>     #89/13   fexit_bpf2bpf/func_replace_progmap:OK
>>     #89      fexit_bpf2bpf:OK
>>     Error: The operation was canceled.
> 
> Let's denylist that test again for now?

Agree, done/pushed now.