Re: [PATCH bpf-next v3 1/2] bpf: add skcipher API support to TC/XDP programs

[Jiri Olsa <olsajiri@gmail.com>]

On Tue, Oct 31, 2023 at 06:48:59AM -0700, Vadim Fedorenko wrote:

SNIP

> diff --git a/kernel/bpf/crypto.c b/kernel/bpf/crypto.c
> new file mode 100644
> index 000000000000..c2a0703934fc
> --- /dev/null
> +++ b/kernel/bpf/crypto.c
> @@ -0,0 +1,280 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright (c) 2023 Meta, Inc */
> +#include <linux/bpf.h>
> +#include <linux/bpf_mem_alloc.h>
> +#include <linux/btf.h>
> +#include <linux/btf_ids.h>
> +#include <linux/filter.h>
> +#include <linux/scatterlist.h>
> +#include <linux/skbuff.h>
> +#include <crypto/skcipher.h>
> +
> +/**
> + * 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.
> + */
> +struct bpf_crypto_skcipher_ctx {
> +	struct crypto_sync_skcipher *tfm;
> +	struct rcu_head rcu;
> +	refcount_t usage;
> +};
> +
> +__diag_push();
> +__diag_ignore_all("-Wmissing-prototypes",
> +		  "Global kfuncs as their definitions will be in BTF");
> +

hi,
just a heads up.. there's [1] change adding macro for this, it's not
merged yet, but will probably get in soon

jirka

[1] https://lore.kernel.org/bpf/20231030210638.2415306-1-davemarchevsky@fb.com/

> +static void *__bpf_dynptr_data_ptr(const struct bpf_dynptr_kern *ptr)
> +{
> +	enum bpf_dynptr_type type;
> +
> +	if (!ptr->data)
> +		return NULL;
> +
> +	type = bpf_dynptr_get_type(ptr);
> +
> +	switch (type) {
> +	case BPF_DYNPTR_TYPE_LOCAL:
> +	case BPF_DYNPTR_TYPE_RINGBUF:
> +		return ptr->data + ptr->offset;
> +	case BPF_DYNPTR_TYPE_SKB:
> +		return skb_pointer_if_linear(ptr->data, ptr->offset, __bpf_dynptr_size(ptr));
> +	case BPF_DYNPTR_TYPE_XDP:
> +	{
> +		void *xdp_ptr = bpf_xdp_pointer(ptr->data, ptr->offset, __bpf_dynptr_size(ptr));
> +		if (!IS_ERR_OR_NULL(xdp_ptr))
> +			return xdp_ptr;
> +
> +		return NULL;
> +	}
> +	default:
> +		WARN_ONCE(true, "unknown dynptr type %d\n", type);
> +		return NULL;
> +	}
> +}
> +
> +/**
> + * bpf_crypto_skcipher_ctx_create() - Create a mutable BPF crypto context.
> + *
> + * Allocates a crypto context that can be used, acquired, and released by
> + * a BPF program. The crypto context returned by this function must either
> + * be embedded in a map as a kptr, or freed with bpf_crypto_skcipher_ctx_release().
> + *
> + * bpf_crypto_skcipher_ctx_create() allocates memory using the BPF memory
> + * allocator, and will not block. It may return NULL if no memory is available.
> + * @algo: bpf_dynptr which holds string representation of algorithm.
> + * @key:  bpf_dynptr which holds cipher key to do crypto.
> + */
> +__bpf_kfunc struct bpf_crypto_skcipher_ctx *
> +bpf_crypto_skcipher_ctx_create(const struct bpf_dynptr_kern *palgo,
> +			       const struct bpf_dynptr_kern *pkey, int *err)
> +{
> +	struct bpf_crypto_skcipher_ctx *ctx;
> +	char *algo;
> +
> +	if (__bpf_dynptr_size(palgo) > CRYPTO_MAX_ALG_NAME) {
> +		*err = -EINVAL;
> +		return NULL;
> +	}
> +
> +	algo = __bpf_dynptr_data_ptr(palgo);
> +
> +	if (!crypto_has_skcipher(algo, CRYPTO_ALG_TYPE_SKCIPHER, CRYPTO_ALG_TYPE_MASK)) {
> +		*err = -EOPNOTSUPP;
> +		return NULL;
> +	}
> +
> +	ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
> +	if (!ctx) {
> +		*err = -ENOMEM;
> +		return NULL;
> +	}
> +
> +	memset(ctx, 0, sizeof(*ctx));
> +
> +	ctx->tfm = crypto_alloc_sync_skcipher(algo, 0, 0);
> +	if (IS_ERR(ctx->tfm)) {
> +		*err = PTR_ERR(ctx->tfm);
> +		ctx->tfm = NULL;
> +		goto err;
> +	}
> +
> +	*err = crypto_sync_skcipher_setkey(ctx->tfm, __bpf_dynptr_data_ptr(pkey),
> +					   __bpf_dynptr_size(pkey));
> +	if (*err)
> +		goto err;
> +
> +	refcount_set(&ctx->usage, 1);
> +
> +	return ctx;
> +err:
> +	if (ctx->tfm)
> +		crypto_free_sync_skcipher(ctx->tfm);
> +	kfree(ctx);
> +
> +	return NULL;
> +}
> +
> +static void crypto_free_sync_skcipher_cb(struct rcu_head *head)
> +{
> +	struct bpf_crypto_skcipher_ctx *ctx;
> +
> +	ctx = container_of(head, struct bpf_crypto_skcipher_ctx, rcu);
> +	crypto_free_sync_skcipher(ctx->tfm);
> +	kfree(ctx);
> +}
> +
> +/**
> + * bpf_crypto_skcipher_ctx_acquire() - Acquire a reference to a BPF crypto context.
> + * @ctx: The BPF crypto context being acquired. The ctx must be a trusted
> + *	     pointer.
> + *
> + * Acquires a reference to a BPF crypto context. The context returned by this function
> + * must either be embedded in a map as a kptr, or freed with
> + * bpf_crypto_skcipher_ctx_release().
> + */
> +__bpf_kfunc struct bpf_crypto_skcipher_ctx *
> +bpf_crypto_skcipher_ctx_acquire(struct bpf_crypto_skcipher_ctx *ctx)
> +{
> +	refcount_inc(&ctx->usage);
> +	return ctx;
> +}
> +
> +/**
> + * bpf_crypto_skcipher_ctx_release() - Release a previously acquired BPF crypto context.
> + * @ctx: The crypto context being released.
> + *
> + * Releases a previously acquired reference to a BPF cpumask. When the final
> + * reference of the BPF cpumask has been released, it is subsequently freed in
> + * an RCU callback in the BPF memory allocator.
> + */
> +__bpf_kfunc void bpf_crypto_skcipher_ctx_release(struct bpf_crypto_skcipher_ctx *ctx)
> +{
> +	if (refcount_dec_and_test(&ctx->usage))
> +		call_rcu(&ctx->rcu, crypto_free_sync_skcipher_cb);
> +}
> +
> +static int bpf_crypto_skcipher_crypt(struct crypto_sync_skcipher *tfm,
> +				     const struct bpf_dynptr_kern *src,
> +				     struct bpf_dynptr_kern *dst,
> +				     const struct bpf_dynptr_kern *iv,
> +				     bool decrypt)
> +{
> +	struct skcipher_request *req = NULL;
> +	struct scatterlist sgin, sgout;
> +	int err;
> +
> +	if (crypto_sync_skcipher_get_flags(tfm) & CRYPTO_TFM_NEED_KEY)
> +		return -EINVAL;
> +
> +	if (__bpf_dynptr_is_rdonly(dst))
> +		return -EINVAL;
> +
> +	if (!__bpf_dynptr_size(dst) || !__bpf_dynptr_size(src))
> +		return -EINVAL;
> +
> +	if (__bpf_dynptr_size(iv) != crypto_sync_skcipher_ivsize(tfm))
> +		return -EINVAL;
> +
> +	req = skcipher_request_alloc(&tfm->base, GFP_ATOMIC);
> +	if (!req)
> +		return -ENOMEM;
> +
> +	sg_init_one(&sgin, __bpf_dynptr_data_ptr(src), __bpf_dynptr_size(src));
> +	sg_init_one(&sgout, __bpf_dynptr_data_ptr(dst), __bpf_dynptr_size(dst));
> +
> +	skcipher_request_set_crypt(req, &sgin, &sgout, __bpf_dynptr_size(src),
> +				   __bpf_dynptr_data_ptr(iv));
> +
> +	err = decrypt ? crypto_skcipher_decrypt(req) : crypto_skcipher_encrypt(req);
> +
> +	skcipher_request_free(req);
> +
> +	return err;
> +}
> +
> +/**
> + * bpf_crypto_skcipher_decrypt() - Decrypt buffer using configured context and IV provided.
> + * @ctx:	The crypto context being used. The ctx must be a trusted pointer.
> + * @src:	bpf_dynptr to the encrypted data. Must be a trusted pointer.
> + * @dst:	bpf_dynptr to the buffer where to store the result. Must be a trusted pointer.
> + * @iv:		bpf_dynptr to IV data to be used by decryptor.
> + *
> + * Decrypts provided buffer using IV data and the crypto context. Crypto context must be configured.
> + */
> +__bpf_kfunc int bpf_crypto_skcipher_decrypt(struct bpf_crypto_skcipher_ctx *ctx,
> +					    const struct bpf_dynptr_kern *src,
> +					    struct bpf_dynptr_kern *dst,
> +					    const struct bpf_dynptr_kern *iv)
> +{
> +	return bpf_crypto_skcipher_crypt(ctx->tfm, src, dst, iv, true);
> +}
> +
> +/**
> + * bpf_crypto_skcipher_encrypt() - Encrypt buffer using configured context and IV provided.
> + * @ctx:	The crypto context being used. The ctx must be a trusted pointer.
> + * @src:	bpf_dynptr to the plain data. Must be a trusted pointer.
> + * @dst:	bpf_dynptr to buffer where to store the result. Must be a trusted pointer.
> + * @iv:		bpf_dynptr to IV data to be used by decryptor.
> + *
> + * Encrypts provided buffer using IV data and the crypto context. Crypto context must be configured.
> + */
> +__bpf_kfunc int bpf_crypto_skcipher_encrypt(struct bpf_crypto_skcipher_ctx *ctx,
> +					    const struct bpf_dynptr_kern *src,
> +					    struct bpf_dynptr_kern *dst,
> +					    const struct bpf_dynptr_kern *iv)
> +{
> +	return bpf_crypto_skcipher_crypt(ctx->tfm, src, dst, iv, false);
> +}
> +
> +__diag_pop();
> +
> +BTF_SET8_START(crypt_skcipher_init_kfunc_btf_ids)
> +BTF_ID_FLAGS(func, bpf_crypto_skcipher_ctx_create, KF_ACQUIRE | KF_RET_NULL | KF_SLEEPABLE)
> +BTF_ID_FLAGS(func, bpf_crypto_skcipher_ctx_release, KF_RELEASE)
> +BTF_ID_FLAGS(func, bpf_crypto_skcipher_ctx_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS)
> +BTF_SET8_END(crypt_skcipher_init_kfunc_btf_ids)
> +
> +static const struct btf_kfunc_id_set crypt_skcipher_init_kfunc_set = {
> +	.owner = THIS_MODULE,
> +	.set   = &crypt_skcipher_init_kfunc_btf_ids,
> +};
> +
> +BTF_SET8_START(crypt_skcipher_kfunc_btf_ids)
> +BTF_ID_FLAGS(func, bpf_crypto_skcipher_decrypt, KF_RCU)
> +BTF_ID_FLAGS(func, bpf_crypto_skcipher_encrypt, KF_RCU)
> +BTF_SET8_END(crypt_skcipher_kfunc_btf_ids)
> +
> +static const struct btf_kfunc_id_set crypt_skcipher_kfunc_set = {
> +	.owner = THIS_MODULE,
> +	.set   = &crypt_skcipher_kfunc_btf_ids,
> +};
> +
> +BTF_ID_LIST(crypto_skcipher_dtor_ids)
> +BTF_ID(struct, bpf_crypto_skcipher_ctx)
> +BTF_ID(func, bpf_crypto_skcipher_ctx_release)
> +
> +static int __init crypto_skcipher_kfunc_init(void)
> +{
> +	int ret;
> +	const struct btf_id_dtor_kfunc crypto_skcipher_dtors[] = {
> +		{
> +			.btf_id	      = crypto_skcipher_dtor_ids[0],
> +			.kfunc_btf_id = crypto_skcipher_dtor_ids[1]
> +		},
> +	};
> +
> +	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &crypt_skcipher_kfunc_set);
> +	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_ACT, &crypt_skcipher_kfunc_set);
> +	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &crypt_skcipher_kfunc_set);
> +	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC,
> +					       &crypt_skcipher_init_kfunc_set);
> +	return  ret ?: register_btf_id_dtor_kfuncs(crypto_skcipher_dtors,
> +						   ARRAY_SIZE(crypto_skcipher_dtors),
> +						   THIS_MODULE);
> +}
> +
> +late_initcall(crypto_skcipher_kfunc_init);
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 62a53ebfedf9..2020884fca3d 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -1429,7 +1429,7 @@ static const struct bpf_func_proto bpf_kptr_xchg_proto = {
>  #define DYNPTR_SIZE_MASK	0xFFFFFF
>  #define DYNPTR_RDONLY_BIT	BIT(31)
>  
> -static bool __bpf_dynptr_is_rdonly(const struct bpf_dynptr_kern *ptr)
> +bool __bpf_dynptr_is_rdonly(const struct bpf_dynptr_kern *ptr)
>  {
>  	return ptr->size & DYNPTR_RDONLY_BIT;
>  }
> @@ -1444,7 +1444,7 @@ static void bpf_dynptr_set_type(struct bpf_dynptr_kern *ptr, enum bpf_dynptr_typ
>  	ptr->size |= type << DYNPTR_TYPE_SHIFT;
>  }
>  
> -static enum bpf_dynptr_type bpf_dynptr_get_type(const struct bpf_dynptr_kern *ptr)
> +enum bpf_dynptr_type bpf_dynptr_get_type(const struct bpf_dynptr_kern *ptr)
>  {
>  	return (ptr->size & ~(DYNPTR_RDONLY_BIT)) >> DYNPTR_TYPE_SHIFT;
>  }
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index bb58987e4844..75d2f47ca3cb 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -5184,6 +5184,7 @@ BTF_ID(struct, prog_test_ref_kfunc)
>  BTF_ID(struct, cgroup)
>  BTF_ID(struct, bpf_cpumask)
>  BTF_ID(struct, task_struct)
> +BTF_ID(struct, bpf_crypto_skcipher_ctx)
>  BTF_SET_END(rcu_protected_types)
>  
>  static bool rcu_protected_object(const struct btf *btf, u32 btf_id)
> -- 
> 2.39.3
> 
>