netdev - Re: [PATCH bpf-next 1/2] bpf: add skcipher API support to TC/XDP programs

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Date: Fri, 27 Oct 2023 13:07:33 +0100
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Jakub Kicinski <kuba@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Alexei Starovoitov <ast@...nel.org>,
 Andrii Nakryiko <andrii@...nel.org>
Cc: Vadim Fedorenko <vadfed@...a.com>, Mykola Lysenko <mykolal@...com>,
 bpf@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next 1/2] bpf: add skcipher API support to TC/XDP
 programs

On 27/10/2023 02:35, Jakub Kicinski wrote:
> On Fri, 27 Oct 2023 00:29:29 +0100 Vadim Fedorenko wrote:
>>> Does anything prevent them from being used simultaneously
>>> by difference CPUs?
>>
>> The algorithm configuration and the key can be used by different CPUs
>> simultaneously
> 
> Makes sense, got confused ctx vs req. You allocate req on the fly.
> 
>>>> +	case BPF_DYNPTR_TYPE_SKB:
>>>> +		return skb_pointer_if_linear(ptr->data, ptr->offset, __bpf_dynptr_size(ptr));
>>>
>>> dynptr takes care of checking if skb can be written to?
>>
>> dynptr is used to take care of size checking, but this particular part is used
>> to provide plain buffer from skb. I'm really sure if we can (or should) encrypt
>> or decrypt in-place, so API now assumes that src and dst are different buffers.
> 
> Not sure this answers my question. What I'm asking is basically whether
> for destination we need to call __bpf_dynptr_is_rdonly() or something
> already checks that.

ah, good point. I'm not sure how to make it better. the
__bpf_dynptr_data_ptr() code is based on bpf_dynptr_slice() which has
bpf_dynptr_slice_rdwr() variant. I don't think it's good idea to add
local rdwr variant. I can either add 2 parameter to force checking if
dynptr isn't read-only, or I can convert bpf_dynptr_slice* functions to
be wrappers over __bpf_dynptr_slice and reuse it in this code.