From: Yonghong Song <yonghong.song@linux.dev>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
Zac Ecob <zacecob@protonmail.com>,
Daniel Borkmann <daniel@iogearbox.net>
Cc: "bpf@vger.kernel.org" <bpf@vger.kernel.org>
Subject: Re: Kernel oops caused by signed divide
Date: Mon, 9 Sep 2024 16:47:19 -0700 [thread overview]
Message-ID: <c6ec9fa2-375d-4db7-ba76-7c78c2a58f1b@linux.dev> (raw)
In-Reply-To: <CAADnVQ+o1jPQwxP9G9Xb=ZSEQDKKq1m1awpovKWdVRMNf8sgdg@mail.gmail.com>
On 9/9/24 10:29 AM, Alexei Starovoitov wrote:
> On Mon, Sep 9, 2024 at 10:21 AM Zac Ecob <zacecob@protonmail.com> wrote:
>> Hello,
>>
>> I recently received a kernel 'oops' about a divide error.
>> After some research, it seems that the 'div64_s64' function used for the 'MOD'/'REM' instructions boils down to an 'idiv'.
>>
>> The 'dividend' is set to INT64_MIN, and the 'divisor' to -1, then because of two's complement, there is no corresponding positive value, causing the error (at least to my understanding).
>>
>>
>> Apologies if this is already known / not a relevant concern.
> Thanks for the report. This is a new issue.
>
> Yonghong,
>
> it's related to the new signed div insn.
> It sounds like we need to update chk_and_div[] part of
> the verifier to account for signed div differently.
Okay. Indeed, INT64_MIN/(-1) cannot be represented.
I will do something similar to chk_and_div[] to filter
out this corner case.
next prev parent reply other threads:[~2024-09-09 23:47 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-09 17:21 Kernel oops caused by signed divide Zac Ecob
2024-09-09 17:27 ` Yonghong Song
2024-09-09 17:29 ` Alexei Starovoitov
2024-09-09 23:47 ` Yonghong Song [this message]
2024-09-10 14:21 ` Yonghong Song
2024-09-10 14:44 ` Dave Thaler
2024-09-10 15:18 ` Yonghong Song
2024-09-10 15:21 ` Alexei Starovoitov
2024-09-10 18:12 ` Yonghong Song
2024-09-10 15:21 ` Alexei Starovoitov
2024-09-10 18:02 ` Yonghong Song
2024-09-10 18:25 ` Alexei Starovoitov
2024-09-10 19:32 ` Yonghong Song
2024-09-10 21:53 ` Alexei Starovoitov
2024-09-10 22:00 ` Yonghong Song
2024-09-10 22:43 ` Andrii Nakryiko
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