From: Jean-Philippe Brucker <jean-philippe@linaro.org>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: sfr@canb.auug.org.au, songliubraving@fb.com, will@kernel.org,
catalin.marinas@arm.com, john.fastabend@gmail.com,
ast@kernel.org, linux-kernel@vger.kernel.org,
linux-next@vger.kernel.org, Qian Cai <cai@lca.pw>,
zlim.lnx@gmail.com, kpsingh@chromium.org, yhs@fb.com,
bpf@vger.kernel.org, andriin@fb.com, kafai@fb.com,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH bpf-next 1/1] arm64: bpf: Add BPF exception tables
Date: Thu, 30 Jul 2020 23:14:53 +0200 [thread overview]
Message-ID: <20200730211453.GA79372@lophozonia> (raw)
In-Reply-To: <f2f05f41-ccf9-e693-85bf-59ebbf8dadfe@iogearbox.net>
On Thu, Jul 30, 2020 at 09:47:39PM +0200, Daniel Borkmann wrote:
> 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.
Yes please squash it into the original patch, sorry for the mess
Thanks,
Jean
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next prev parent reply other threads:[~2020-07-30 21:16 UTC|newest]
Thread overview: 15+ 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 ` [PATCH bpf-next 1/1] arm64: bpf: " Jean-Philippe Brucker
2020-07-29 17:28 ` Song Liu
2020-07-29 21:29 ` Daniel Borkmann
2020-07-30 8:28 ` Jean-Philippe Brucker
2020-07-30 12:28 ` Qian Cai
2020-07-30 14:22 ` Jean-Philippe Brucker
2020-07-30 19:47 ` Daniel Borkmann
2020-07-30 21:14 ` Jean-Philippe Brucker [this message]
2020-07-30 22:45 ` Daniel Borkmann
2021-06-09 12:04 ` [PATCH bpf-next 0/1] arm64: " Ravi Bangoria
2021-06-11 0:12 ` Alexei Starovoitov
2021-06-17 6:58 ` Ravi Bangoria
2021-06-18 16:34 ` Alexei Starovoitov
2021-06-22 7:10 ` Ravi Bangoria
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