linux-kernel - Re: [PATCH v2 bpf-next 2/2] selftests/bpf: add exception handling selftests for tp

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Date:   Fri, 5 Nov 2021 11:54:27 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alan Maguire <alan.maguire@...cle.com>
Cc:     ardb@...nel.org, Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, andreyknvl@...il.com,
        vincenzo.frascino@....com, Mark Rutland <mark.rutland@....com>,
        Sami Tolvanen <samitolvanen@...gle.com>, joey.gouly@....com,
        maz@...nel.org, daizhiyuan@...tium.com.cn, jthierry@...hat.com,
        Tian Tao <tiantao6@...ilicon.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, rppt@...nel.org,
        Jisheng.Zhang@...aptics.com,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next 2/2] selftests/bpf: add exception handling
 selftests for tp_bpf program

On Fri, Nov 5, 2021 at 10:11 AM Alan Maguire <alan.maguire@...cle.com> wrote:
>
> Exception handling is triggered in BPF tracing programs when
> a NULL pointer is dereferenced; the exception handler zeroes the
> target register and execution of the BPF program progresses.
>
> To test exception handling then, we need to trigger a NULL pointer
> dereference for a field which should never be zero; if it is, the
> only explanation is the exception handler ran.  task->task_works
> is the NULL pointer chosen (for a new task from fork() no work
> is associated), and the task_works->func field should not be zero
> if task_works is non-NULL.  Test verifies task_works and
> task_works->func are 0.
>
> Signed-off-by: Alan Maguire <alan.maguire@...cle.com>
> ---
>  tools/testing/selftests/bpf/prog_tests/exhandler.c | 43 ++++++++++++++++++++++
>  tools/testing/selftests/bpf/progs/exhandler_kern.c | 43 ++++++++++++++++++++++
>  2 files changed, 86 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/exhandler.c
>  create mode 100644 tools/testing/selftests/bpf/progs/exhandler_kern.c
>

The test looks good, thank you!

Acked-by: Andrii Nakryiko <andrii@...nel.org>

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