netdev - Re: arch: arm: bpf: Converting cBPF to eBPF for arm 32 bit

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Date:   Mon, 22 May 2017 21:27:57 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Shubham Bansal <illusionist.neo@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        Mircea Gherzan <mgherzan@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>, ast@...com
Subject: Re: arch: arm: bpf: Converting cBPF to eBPF for arm 32 bit

On Mon, May 22, 2017 at 7:58 PM, Shubham Bansal
<illusionist.neo@...il.com> wrote:
> On testing the eBPF JIT with CONFIG_FRAME_POINTER I got the following
> crash for non jitted testcase.

It's just a softlockup WARN, not a crash, and I think it'd to be
expected given the large runtime test_bpf reports:

> [   72.032494] test_bpf: #267 BPF_MAXINSNS: Call heavy transformations
> jited:0 1112799
> [   92.304815] NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s!
> [insmod:104]
> ...
> [   93.835343] 1065840 PASS

https://www.kernel.org/doc/Documentation/lockup-watchdogs.txt

You can raise the softlockup time-out by changing the number of
seconds here: /proc/sys/kernel/watchdog_thresh I think the softlockup
is counting the entire runtime of the bpf_tests run, so if it takes 30
seconds to run, put at least 15 into /proc/sys/kernel/watchdog_thresh

-Kees

-- 
Kees Cook
Pixel Security