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From: Song Liu <song@kernel.org>
To: Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org, bpf <bpf@vger.kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Alexei Starovoitov <ast@kernel.org>,
	zlim.lnx@gmail.com, Martin KaFai Lau <kafai@fb.com>,
	Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
	Andrii Nakryiko <andriin@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>
Subject: Re: [PATCH bpf-next 1/1] arm64: bpf: Add BPF exception tables
Date: Wed, 29 Jul 2020 10:28:49 -0700	[thread overview]
Message-ID: <CAPhsuW5CmQzELjc8+tQVWZStjPxENhGB7066YJLp=ANs8BYiHA@mail.gmail.com> (raw)
In-Reply-To: <20200728152122.1292756-2-jean-philippe@linaro.org>

On Tue, Jul 28, 2020 at 8:37 AM Jean-Philippe Brucker
<jean-philippe@linaro.org> 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 patch looks good to me.

Acked-by: Song Liu <songliubraving@fb.com>

It is possible to add a selftest for this? I thought about this a
little bit, but
didn't get a good idea.

Thanks,
Song

WARNING: multiple messages have this Message-ID (diff)
From: Song Liu <song@kernel.org>
To: Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc: Song Liu <songliubraving@fb.com>,
	Andrii Nakryiko <andriin@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Catalin Marinas <catalin.marinas@arm.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Alexei Starovoitov <ast@kernel.org>,
	zlim.lnx@gmail.com, KP Singh <kpsingh@chromium.org>,
	Yonghong Song <yhs@fb.com>, bpf <bpf@vger.kernel.org>,
	Will Deacon <will@kernel.org>, Martin KaFai Lau <kafai@fb.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH bpf-next 1/1] arm64: bpf: Add BPF exception tables
Date: Wed, 29 Jul 2020 10:28:49 -0700	[thread overview]
Message-ID: <CAPhsuW5CmQzELjc8+tQVWZStjPxENhGB7066YJLp=ANs8BYiHA@mail.gmail.com> (raw)
In-Reply-To: <20200728152122.1292756-2-jean-philippe@linaro.org>

On Tue, Jul 28, 2020 at 8:37 AM Jean-Philippe Brucker
<jean-philippe@linaro.org> 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 patch looks good to me.

Acked-by: Song Liu <songliubraving@fb.com>

It is possible to add a selftest for this? I thought about this a
little bit, but
didn't get a good idea.

Thanks,
Song

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2020-07-29 17:29 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-28 15:21 [PATCH bpf-next 0/1] arm64: Add BPF exception tables Jean-Philippe Brucker
2020-07-28 15:21 ` Jean-Philippe Brucker
2020-07-28 15:21 ` [PATCH bpf-next 1/1] arm64: bpf: " Jean-Philippe Brucker
2020-07-28 15:21   ` Jean-Philippe Brucker
2020-07-29 17:28   ` Song Liu [this message]
2020-07-29 17:28     ` Song Liu
2020-07-29 21:29     ` Daniel Borkmann
2020-07-29 21:29       ` Daniel Borkmann
2020-07-30  8:28       ` Jean-Philippe Brucker
2020-07-30  8:28         ` Jean-Philippe Brucker
2020-07-30 12:28   ` Qian Cai
2020-07-30 12:28     ` Qian Cai
2020-07-30 14:22     ` Jean-Philippe Brucker
2020-07-30 14:22       ` Jean-Philippe Brucker
2020-07-30 19:47       ` Daniel Borkmann
2020-07-30 19:47         ` Daniel Borkmann
2020-07-30 21:14         ` Jean-Philippe Brucker
2020-07-30 21:14           ` Jean-Philippe Brucker
2020-07-30 22:45           ` Daniel Borkmann
2020-07-30 22:45             ` Daniel Borkmann
2021-06-09 12:04 ` [PATCH bpf-next 0/1] arm64: " Ravi Bangoria
2021-06-09 12:04   ` Ravi Bangoria
2021-06-11  0:12   ` Alexei Starovoitov
2021-06-11  0:12     ` Alexei Starovoitov
2021-06-17  6:58     ` Ravi Bangoria
2021-06-17  6:58       ` Ravi Bangoria
2021-06-18 16:34       ` Alexei Starovoitov
2021-06-18 16:34         ` Alexei Starovoitov
2021-06-22  7:10         ` Ravi Bangoria
2021-06-22  7:10           ` Ravi Bangoria
2021-06-22 11:00         ` [PATCH] x86 bpf: Fix extable offset calculation Ravi Bangoria
2021-06-25  4:01           ` Alexei Starovoitov
2021-06-25  6:22             ` Ravi Bangoria
2021-06-25 15:07               ` Alexei Starovoitov

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