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From: Martin KaFai Lau <martin.lau@linux.dev>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Hou Tao <houtao@huaweicloud.com>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>,
	Yonghong Song <yhs@meta.com>, bpf <bpf@vger.kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>, Song Liu <song@kernel.org>,
	Hao Luo <haoluo@google.com>, Yonghong Song <yhs@fb.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	KP Singh <kpsingh@kernel.org>,
	Stanislav Fomichev <sdf@google.com>, Jiri Olsa <jolsa@kernel.org>,
	John Fastabend <john.fastabend@gmail.com>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	rcu@vger.kernel.org, Hou Tao <houtao1@huawei.com>,
	Martin KaFai Lau <martin.lau@kernel.org>
Subject: Re: [RFC PATCH bpf-next 0/6] bpf: Handle reuse in bpf memory alloc
Date: Tue, 14 Feb 2023 17:54:26 -0800	[thread overview]
Message-ID: <6d48c284-42eb-9688-4259-79b7f096e294@linux.dev> (raw)
In-Reply-To: <CAADnVQJzS9MQKS2EqrdxO7rVLyjUYD6OG-Yefak62-JRNcheZg@mail.gmail.com>

On 2/11/23 8:34 AM, Alexei Starovoitov wrote:
> On Sat, Feb 11, 2023 at 8:33 AM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
>> On Fri, Feb 10, 2023 at 5:10 PM Hou Tao <houtao@huaweicloud.com> wrote:
>>>>> Hou, are you plannning to resubmit this change? I also hit this while testing my
>>>>> changes on bpf-next.
>>>> Are you talking about the whole patch set or just GFP_ZERO in mem_alloc?
>>>> The former will take a long time to settle.
>>>> The latter is trivial.
>>>> To unblock yourself just add GFP_ZERO in an extra patch?
>>> Sorry for the long delay. Just find find out time to do some tests to compare
>>> the performance of bzero and ctor. After it is done, will resubmit on next week.
>> I still don't like ctor as a concept. In general the callbacks in the critical
>> path are guaranteed to be slow due to retpoline overhead.
>> Please send a patch to add GFP_ZERO.
>> Also I realized that we can make the BPF_REUSE_AFTER_RCU_GP flag usable
>> without risking OOM by only waiting for normal rcu GP and not rcu_tasks_trace.
>> This approach will work for inner nodes of qptrie, since bpf progs
>> never see pointers to them. It will work for local storage
>> converted to bpf_mem_alloc too. It wouldn't need to use its own call_rcu.
>> It's also safe without uaf caveat in sleepable progs and sleepable progs
> I meant 'safe with uaf caveat'.
> Safe because we wait for rcu_task_trace later before returning to kernel memory.

For local storage, when its owner (sk/task/inode/cgrp) is going away, the memory 
can be reused immediately. No rcu gp is needed.

The local storage delete case (eg. bpf_sk_storage_delete) is the only one that 
needs to be freed by tasks_trace gp because another bpf prog (reader) may be 
under the rcu_read_lock_trace(). I think the idea (BPF_REUSE_AFTER_RCU_GP) on 
allowing reuse after vanilla rcu gp and free (if needed) after tasks_trace gp 
can be extended to the local storage delete case. I think we can extend the 
assumption that "sleepable progs (reader) can use explicit bpf_rcu_read_lock() 
when they want to avoid uaf" to bpf_{sk,task,inode,cgrp}_storage_get() also.

I also need the GFP_ZERO in bpf_mem_alloc, so will work on the GFP_ZERO and the 
BPF_REUSE_AFTER_RCU_GP idea.  Probably will get the GFP_ZERO out first.

>> can use explicit bpf_rcu_read_lock() when they want to avoid uaf.
>> So please respin the set with rcu gp only and that new flag.

  reply	other threads:[~2023-02-15  1:54 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-30  4:11 [RFC PATCH bpf-next 0/6] bpf: Handle reuse in bpf memory alloc Hou Tao
2022-12-30  4:11 ` [RFC PATCH bpf-next 1/6] bpf: Support ctor in bpf memory allocator Hou Tao
2022-12-30  4:11 ` [RFC PATCH bpf-next 2/6] bpf: Factor out a common helper free_llist() Hou Tao
2022-12-30  4:11 ` [RFC PATCH bpf-next 3/6] bpf: Pass bitwise flags to bpf_mem_alloc_init() Hou Tao
2022-12-30  4:11 ` [RFC PATCH bpf-next 4/6] bpf: Introduce BPF_MA_NO_REUSE for bpf memory allocator Hou Tao
2022-12-30  4:11 ` [RFC PATCH bpf-next 5/6] bpf: Use BPF_MA_NO_REUSE in htab map Hou Tao
2022-12-30  4:11 ` [RFC PATCH bpf-next 6/6] selftests/bpf: Add test case for element reuse " Hou Tao
2023-01-01  1:26 ` [RFC PATCH bpf-next 0/6] bpf: Handle reuse in bpf memory alloc Alexei Starovoitov
2023-01-01 18:48   ` Yonghong Song
2023-01-03 13:47     ` Hou Tao
2023-01-04  6:10       ` Yonghong Song
2023-01-04  6:30         ` Hou Tao
2023-01-04  7:14           ` Yonghong Song
2023-01-04 18:26             ` Alexei Starovoitov
2023-02-10 16:32               ` Kumar Kartikeya Dwivedi
2023-02-10 21:06                 ` Alexei Starovoitov
2023-02-11  1:09                   ` Hou Tao
2023-02-11 16:33                     ` Alexei Starovoitov
2023-02-11 16:34                       ` Alexei Starovoitov
2023-02-15  1:54                         ` Martin KaFai Lau [this message]
2023-02-15  4:02                           ` Hou Tao
2023-02-15  7:22                             ` Martin KaFai Lau
2023-02-16  2:11                               ` Hou Tao
2023-02-16  7:47                                 ` Martin KaFai Lau
2023-02-16  8:18                                   ` Hou Tao
2023-02-16 13:55                         ` Hou Tao
2023-02-16 16:35                           ` Alexei Starovoitov
2023-02-17  1:19                             ` Hou Tao
2023-02-22 19:30                               ` Alexei Starovoitov
2023-02-15  2:35                       ` Hou Tao
2023-02-15  2:42                         ` Alexei Starovoitov
2023-02-15  3:00                           ` Hou Tao
2023-01-03 13:40   ` Hou Tao
2023-01-03 19:38     ` Alexei Starovoitov
2023-01-10  6:26       ` Martin KaFai Lau

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