From: Daniel Borkmann <daniel@iogearbox.net>
To: Jean-Philippe Brucker <jean-philippe@linaro.org>, Qian Cai <cai@lca.pw>
Cc: linux-arm-kernel@lists.infradead.org, bpf@vger.kernel.org,
songliubraving@fb.com, andriin@fb.com, catalin.marinas@arm.com,
john.fastabend@gmail.com, ast@kernel.org, zlim.lnx@gmail.com,
kpsingh@chromium.org, yhs@fb.com, will@kernel.org, kafai@fb.com,
sfr@canb.auug.org.au, linux-next@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf-next 1/1] arm64: bpf: Add BPF exception tables
Date: Thu, 30 Jul 2020 21:47:39 +0200 [thread overview]
Message-ID: <f2f05f41-ccf9-e693-85bf-59ebbf8dadfe@iogearbox.net> (raw)
In-Reply-To: <20200730142213.GB1529030@myrica>
On 7/30/20 4:22 PM, Jean-Philippe Brucker wrote:
> On Thu, Jul 30, 2020 at 08:28:56AM -0400, Qian Cai wrote:
>> On Tue, Jul 28, 2020 at 05:21:26PM +0200, Jean-Philippe Brucker wrote:
>>> When a tracing BPF program attempts to read memory without using the
>>> bpf_probe_read() helper, the verifier marks the load instruction with
>>> the BPF_PROBE_MEM flag. Since the arm64 JIT does not currently recognize
>>> this flag it falls back to the interpreter.
>>>
>>> Add support for BPF_PROBE_MEM, by appending an exception table to the
>>> BPF program. If the load instruction causes a data abort, the fixup
>>> infrastructure finds the exception table and fixes up the fault, by
>>> clearing the destination register and jumping over the faulting
>>> instruction.
>>>
>>> To keep the compact exception table entry format, inspect the pc in
>>> fixup_exception(). A more generic solution would add a "handler" field
>>> to the table entry, like on x86 and s390.
>>>
>>> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
>>
>> This will fail to compile on arm64,
>>
>> https://gitlab.com/cailca/linux-mm/-/blob/master/arm64.config
>>
>> arch/arm64/mm/extable.o: In function `fixup_exception':
>> arch/arm64/mm/extable.c:19: undefined reference to `arm64_bpf_fixup_exception'
>
> Thanks for the report, I attached a fix. Daniel, can I squash it and
> resend as v2 or is it too late?
If you want I can squash your attached snippet into the original patch of
yours. If you want to send a v2 that is fine as well of course. Let me know.
Thanks,
Daniel
next prev parent reply other threads:[~2020-07-30 19:47 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200728152122.1292756-1-jean-philippe@linaro.org>
[not found] ` <20200728152122.1292756-2-jean-philippe@linaro.org>
2020-07-30 12:28 ` [PATCH bpf-next 1/1] arm64: bpf: Add BPF exception tables Qian Cai
2020-07-30 14:22 ` Jean-Philippe Brucker
2020-07-30 19:47 ` Daniel Borkmann [this message]
2020-07-30 21:14 ` Jean-Philippe Brucker
2020-07-30 22:45 ` Daniel Borkmann
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