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

From: Jakub Kicinski <[email-masked]>
Date: Thu, 26 Oct 2023 14:47:59 -0700

On Wed, 25 Oct 2023 18:59:37 -0700 Vadim Fedorenko wrote:
> Add crypto API support to BPF to be able to decrypt or encrypt packets
> in TC/XDP BPF programs. Only symmetric key ciphers are supported for
> now. Special care should be taken for initialization part of crypto algo
> because crypto_alloc_sync_skcipher() doesn't work with preemtion
> disabled, it can be run only in sleepable BPF program. Also async crypto
> is not supported because of the very same issue - TC/XDP BPF programs
> are not sleepable.

Do CC crypto@ for the next version, please.

> +/**
> + * struct bpf_crypto_skcipher_ctx - refcounted BPF sync skcipher context structure
> + * @tfm:	The pointer to crypto_sync_skcipher struct.
> + * @rcu:	The RCU head used to free the crypto context with RCU safety.
> + * @usage:	Object reference counter. When the refcount goes to 0, the
> + *		memory is released back to the BPF allocator, which provides
> + *		RCU safety.
> + */
> +

spurious newline?

> +struct bpf_crypto_skcipher_ctx {

> +/**
> + * bpf_crypto_skcipher_ctx_acquire() - Acquire a reference to a BPF crypto context.

The contexts are refcounted and can be placed in maps?
Does anything prevent them from being used simultaneously 
by difference CPUs?

> +	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?