netdev - Re: [PATCH bpf-next 3/4] bpf: Fix net.core.bpf_jit

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Date:   Thu, 10 Mar 2022 09:01:46 +0800
From:   Hou Tao <houtao1@...wei.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        Yonghong Song <yhs@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        KP Singh <kpsingh@...nel.org>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 3/4] bpf: Fix net.core.bpf_jit_harden race

Hi,

On 3/10/2022 7:22 AM, Alexei Starovoitov wrote:
> On Wed, Mar 09, 2022 at 08:33:20PM +0800, Hou Tao wrote:
>> It is the bpf_jit_harden counterpart to commit 60b58afc96c9 ("bpf: fix
>> net.core.bpf_jit_enable race"). bpf_jit_harden will be tested twice
>> for each subprog if there are subprogs in bpf program and constant
>> blinding may increase the length of program, so when running
>> "./test_progs -t subprogs" and toggling bpf_jit_harden between 0 and 2,
>> jit_subprogs may fail because constant blinding increases the length
>> of subprog instructions during extra passs.
>>
>> So cache the value of bpf_jit_blinding_enabled() during program
>> allocation, and use the cached value during constant blinding, subprog
>> JITing and args tracking of tail call.
> Looks like this patch alone is enough.
> With race fixed. Patches 1 and 2 are no longer necessary, right?
Yes and no. With patch 3 applied, the problems described in patch 1 and patch 2
are gone, but it may recur due to other issue in JIT. So I post these two patch
together and hope these fixes can also be merged.
> .