Subject: Re: [PATCH] bpf: optimize constant blinding

From: Jiong Wang <[email-masked]>
Date: Wed, 12 Jun 2019 16:04:56 +0100

Alexei Starovoitov writes:

> On Wed, Jun 12, 2019 at 4:32 AM Naveen N. Rao
> <[email-masked]> wrote:
>>
>> Currently, for constant blinding, we re-allocate the bpf program to
>> account for its new size and adjust all branches to accommodate the
>> same, for each BPF instruction that needs constant blinding. This is
>> inefficient and can lead to soft lockup with sufficiently large
>> programs, such as the new verifier scalability test (ld_dw: xor
>> semi-random 64 bit imms, test 5 -- with net.core.bpf_jit_harden=2)
>
> Slowdown you see is due to patch_insn right?
> In such case I prefer to fix the scaling issue of patch_insn instead.
> This specific fix for blinding only is not addressing the core of the problem.
> Jiong,
> how is the progress on fixing patch_insn?

I actually was about to reply this email as we have discussed exactly the
same issue on jit blinding here:

  https://www.spinics.net/lists/bpf/msg01836.html

And sorry for the slow progress on fixing patch_insn, please give me one
more week, I will try to send out a RFC for it.

Regards,
Jiong