[PATCH bpf-next 1/1] arm64: bpf: Add BPF exception tables

[Song Liu]

On Tue, Jul 28, 2020 at 8:37 AM Jean-Philippe Brucker
<jean-philippe at 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 at linaro.org>

This patch looks good to me.

Acked-by: Song Liu <songliubraving at 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