Subject: Re: [PATCH bpf-next v8 1/3] bpf: make common crypto API for TC/XDP programs

From: Vadim Fedorenko <[email-masked]>
Date: Tue, 23 Jan 2024 17:51:50 +0000

gentle ping here? it's more than a week with no feedback...

thanks

On 15/01/2024 22:08, Vadim Fedorenko wrote:
> Add crypto API support to BPF to be able to decrypt or encrypt packets
> in TC/XDP BPF programs. Special care should be taken for initialization
> part of crypto algo because crypto alloc) 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.
> 
> Signed-off-by: Vadim Fedorenko <[email-masked]>
> ---
> v7 -> v8:
> - add statesize ops to bpf crypto type as some ciphers are now stateful
> - improve error path in bpf_crypto_create
> v6 -> v7:
> - style fixes
> v5 -> v6:
> - replace lskcipher with infrastructure to provide pluggable cipher
>    types
> - add BPF skcipher as plug-in module in a separate patch
> v4 -> v5:
> - replace crypto API to use lskcipher (suggested by Herbert Xu)
> - remove SG list usage and provide raw buffers
> v3 -> v4:
> - reuse __bpf_dynptr_data and remove own implementation
> - use const __str to provide algorithm name
> - use kfunc macroses to avoid compilator warnings
> v2 -> v3:
> - fix kdoc issues
> v1 -> v2:
> - use kmalloc in sleepable func, suggested by Alexei
> - use __bpf_dynptr_is_rdonly() to check destination, suggested by Jakub
> - use __bpf_dynptr_data_ptr() for all dynptr accesses
> ---
>   include/linux/bpf.h        |   1 +
>   include/linux/bpf_crypto.h |  24 +++
>   kernel/bpf/Makefile        |   3 +
>   kernel/bpf/crypto.c        | 366 +++++++++++++++++++++++++++++++++++++
>   kernel/bpf/helpers.c       |   2 +-
>   kernel/bpf/verifier.c      |   1 +
>   6 files changed, 396 insertions(+), 1 deletion(-)
>   create mode 100644 include/linux/bpf_crypto.h
>   create mode 100644 kernel/bpf/crypto.c
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 377857b232c6..54fc30c64d19 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1263,6 +1263,7 @@ int bpf_dynptr_check_size(u32 size);
>   u32 __bpf_dynptr_size(const struct bpf_dynptr_kern *ptr);
>   const void *__bpf_dynptr_data(const struct bpf_dynptr_kern *ptr, u32 len);
>   void *__bpf_dynptr_data_rw(const struct bpf_dynptr_kern *ptr, u32 len);
> +bool __bpf_dynptr_is_rdonly(const struct bpf_dynptr_kern *ptr);
>   
>   #ifdef CONFIG_BPF_JIT
>   int bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr);
> diff --git a/include/linux/bpf_crypto.h b/include/linux/bpf_crypto.h
> new file mode 100644
> index 000000000000..8456b7477e1d
> --- /dev/null
> +++ b/include/linux/bpf_crypto.h
> @@ -0,0 +1,24 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
> +#ifndef _BPF_CRYPTO_H
> +#define _BPF_CRYPTO_H
> +
> +struct bpf_crypto_type {
> +	void *(*alloc_tfm)(const char *algo);
> +	void (*free_tfm)(void *tfm);
> +	int (*has_algo)(const char *algo);
> +	int (*setkey)(void *tfm, const u8 *key, unsigned int keylen);
> +	int (*setauthsize)(void *tfm, unsigned int authsize);
> +	int (*encrypt)(void *tfm, const u8 *src, u8 *dst, unsigned int len, u8 *iv);
> +	int (*decrypt)(void *tfm, const u8 *src, u8 *dst, unsigned int len, u8 *iv);
> +	unsigned int (*ivsize)(void *tfm);
> +	unsigned int (*statesize)(void *tfm);
> +	u32 (*get_flags)(void *tfm);
> +	struct module *owner;
> +	char name[14];
> +};
> +
> +int bpf_crypto_register_type(const struct bpf_crypto_type *type);
> +int bpf_crypto_unregister_type(const struct bpf_crypto_type *type);
> +
> +#endif /* _BPF_CRYPTO_H */
> diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> index f526b7573e97..bcde762bb2c2 100644
> --- a/kernel/bpf/Makefile
> +++ b/kernel/bpf/Makefile
> @@ -41,6 +41,9 @@ obj-$(CONFIG_BPF_SYSCALL) += bpf_struct_ops.o
>   obj-$(CONFIG_BPF_SYSCALL) += cpumask.o
>   obj-${CONFIG_BPF_LSM} += bpf_lsm.o
>   endif
> +ifeq ($(CONFIG_CRYPTO),y)
> +obj-$(CONFIG_BPF_SYSCALL) += crypto.o
> +endif
>   obj-$(CONFIG_BPF_PRELOAD) += preload/
>   
>   obj-$(CONFIG_BPF_SYSCALL) += relo_core.o
> diff --git a/kernel/bpf/crypto.c b/kernel/bpf/crypto.c
> new file mode 100644
> index 000000000000..74b06e7122d2
> --- /dev/null
> +++ b/kernel/bpf/crypto.c
> @@ -0,0 +1,366 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright (c) 2023 Meta, Inc */
> +#include <linux/bpf.h>
> +#include <linux/bpf_crypto.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_type_list {
> +	const struct bpf_crypto_type *type;
> +	struct list_head list;
> +};
> +
> +static LIST_HEAD(bpf_crypto_types);
> +static DECLARE_RWSEM(bpf_crypto_types_sem);
> +
> +/**
> + * struct bpf_crypto_ctx - refcounted BPF crypto context structure
> + * @type:	The pointer to bpf crypto type
> + * @tfm:	The pointer to instance of crypto API 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_ctx {
> +	const struct bpf_crypto_type *type;
> +	void *tfm;
> +	struct rcu_head rcu;
> +	refcount_t usage;
> +};
> +
> +int bpf_crypto_register_type(const struct bpf_crypto_type *type)
> +{
> +	struct bpf_crypto_type_list *node;
> +	int err = -EEXIST;
> +
> +	down_write(&bpf_crypto_types_sem);
> +	list_for_each_entry(node, &bpf_crypto_types, list) {
> +		if (!strcmp(node->type->name, type->name))
> +			goto unlock;
> +	}
> +
> +	node = kmalloc(sizeof(*node), GFP_KERNEL);
> +	err = -ENOMEM;
> +	if (!node)
> +		goto unlock;
> +
> +	node->type = type;
> +	list_add(&node->list, &bpf_crypto_types);
> +	err = 0;
> +
> +unlock:
> +	up_write(&bpf_crypto_types_sem);
> +
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(bpf_crypto_register_type);
> +
> +int bpf_crypto_unregister_type(const struct bpf_crypto_type *type)
> +{
> +	struct bpf_crypto_type_list *node;
> +	int err = -ENOENT;
> +
> +	down_write(&bpf_crypto_types_sem);
> +	list_for_each_entry(node, &bpf_crypto_types, list) {
> +		if (strcmp(node->type->name, type->name))
> +			continue;
> +
> +		list_del(&node->list);
> +		kfree(node);
> +		err = 0;
> +		break;
> +	}
> +	up_write(&bpf_crypto_types_sem);
> +
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(bpf_crypto_unregister_type);
> +
> +static const struct bpf_crypto_type *bpf_crypto_get_type(const char *name)
> +{
> +	const struct bpf_crypto_type *type = ERR_PTR(-ENOENT);
> +	struct bpf_crypto_type_list *node;
> +
> +	down_read(&bpf_crypto_types_sem);
> +	list_for_each_entry(node, &bpf_crypto_types, list) {
> +		if (strcmp(node->type->name, name))
> +			continue;
> +
> +		if (try_module_get(node->type->owner))
> +			type = node->type;
> +		break;
> +	}
> +	up_read(&bpf_crypto_types_sem);
> +
> +	return type;
> +}
> +
> +__bpf_kfunc_start_defs();
> +
> +/**
> + * bpf_crypto_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_ctx_release().
> + * As crypto API functions use GFP_KERNEL allocations, this function can
> + * only be used in sleepable BPF programs.
> + *
> + * bpf_crypto_ctx_create() allocates memory for crypto context.
> + * It may return NULL if no memory is available.
> + * @type__str: pointer to string representation of crypto type.
> + * @algo__str: pointer to string representation of algorithm.
> + * @pkey:      bpf_dynptr which holds cipher key to do crypto.
> + * @authsize:  the size of authentication data in case of AEAD transformation
> + * @err:       integer to store error code when NULL is returned
> + */
> +__bpf_kfunc struct bpf_crypto_ctx *
> +bpf_crypto_ctx_create(const char *type__str, const char *algo__str,
> +		      const struct bpf_dynptr_kern *pkey,
> +		      unsigned int authsize, int *err)
> +{
> +	const struct bpf_crypto_type *type = bpf_crypto_get_type(type__str);
> +	struct bpf_crypto_ctx *ctx;
> +	const u8 *key;
> +	u32 key_len;
> +
> +	type = bpf_crypto_get_type(type__str);
> +	if (IS_ERR(type)) {
> +		*err = PTR_ERR(type);
> +		return NULL;
> +	}
> +
> +	if (!type->has_algo(algo__str)) {
> +		*err = -EOPNOTSUPP;
> +		goto err_module_put;
> +	}
> +
> +	if (!authsize && type->setauthsize) {
> +		*err = -EOPNOTSUPP;
> +		goto err_module_put;
> +	}
> +
> +	if (authsize && !type->setauthsize) {
> +		*err = -EOPNOTSUPP;
> +		goto err_module_put;
> +	}
> +
> +	key_len = __bpf_dynptr_size(pkey);
> +	if (!key_len) {
> +		*err = -EINVAL;
> +		goto err_module_put;
> +	}
> +	key = __bpf_dynptr_data(pkey, key_len);
> +	if (!key) {
> +		*err = -EINVAL;
> +		goto err_module_put;
> +	}
> +
> +	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
> +	if (!ctx) {
> +		*err = -ENOMEM;
> +		goto err_module_put;
> +	}
> +
> +	ctx->type = type;
> +	ctx->tfm = type->alloc_tfm(algo__str);
> +	if (IS_ERR(ctx->tfm)) {
> +		*err = PTR_ERR(ctx->tfm);
> +		goto err_free_ctx;
> +	}
> +
> +	if (authsize) {
> +		*err = type->setauthsize(ctx->tfm, authsize);
> +		if (*err)
> +			goto err_free_tfm;
> +	}
> +
> +	*err = type->setkey(ctx->tfm, key, key_len);
> +	if (*err)
> +		goto err_free_tfm;
> +
> +	refcount_set(&ctx->usage, 1);
> +
> +	return ctx;
> +
> +err_free_tfm:
> +	type->free_tfm(ctx->tfm);
> +err_free_ctx:
> +	kfree(ctx);
> +err_module_put:
> +	module_put(type->owner);
> +
> +	return NULL;
> +}
> +
> +static void crypto_free_cb(struct rcu_head *head)
> +{
> +	struct bpf_crypto_ctx *ctx;
> +
> +	ctx = container_of(head, struct bpf_crypto_ctx, rcu);
> +	ctx->type->free_tfm(ctx->tfm);
> +	module_put(ctx->type->owner);
> +	kfree(ctx);
> +}
> +
> +/**
> + * bpf_crypto_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_ctx *
> +bpf_crypto_ctx_acquire(struct bpf_crypto_ctx *ctx)
> +{
> +	refcount_inc(&ctx->usage);
> +	return ctx;
> +}
> +
> +/**
> + * bpf_crypto_ctx_release() - Release a previously acquired BPF crypto context.
> + * @ctx: The crypto context being released.
> + *
> + * Releases a previously acquired reference to a BPF crypto context. When the final
> + * reference of the BPF crypto context has been released, it is subsequently freed in
> + * an RCU callback in the BPF memory allocator.
> + */
> +__bpf_kfunc void bpf_crypto_ctx_release(struct bpf_crypto_ctx *ctx)
> +{
> +	if (refcount_dec_and_test(&ctx->usage))
> +		call_rcu(&ctx->rcu, crypto_free_cb);
> +}
> +
> +static int bpf_crypto_crypt(const struct bpf_crypto_ctx *ctx,
> +			    const struct bpf_dynptr_kern *src,
> +			    struct bpf_dynptr_kern *dst,
> +			    const struct bpf_dynptr_kern *siv,
> +			    bool decrypt)
> +{
> +	u32 src_len, dst_len, siv_len;
> +	const u8 *psrc;
> +	u8 *pdst, *piv;
> +	int err;
> +
> +	if (ctx->type->get_flags(ctx->tfm) & CRYPTO_TFM_NEED_KEY)
> +		return -EINVAL;
> +
> +	if (__bpf_dynptr_is_rdonly(dst))
> +		return -EINVAL;
> +
> +	siv_len = __bpf_dynptr_size(siv);
> +	src_len = __bpf_dynptr_size(src);
> +	dst_len = __bpf_dynptr_size(dst);
> +	if (!src_len || !dst_len)
> +		return -EINVAL;
> +
> +	if (siv_len != (ctx->type->ivsize(ctx->tfm) + ctx->type->statesize(ctx->tfm)))
> +		return -EINVAL;
> +
> +	psrc = __bpf_dynptr_data(src, src_len);
> +	if (!psrc)
> +		return -EINVAL;
> +	pdst = __bpf_dynptr_data_rw(dst, dst_len);
> +	if (!pdst)
> +		return -EINVAL;
> +
> +	piv = siv_len ? __bpf_dynptr_data_rw(siv, siv_len) : NULL;
> +	if (siv_len && !piv)
> +		return -EINVAL;
> +
> +	err = decrypt ? ctx->type->decrypt(ctx->tfm, psrc, pdst, src_len, piv)
> +		      : ctx->type->encrypt(ctx->tfm, psrc, pdst, src_len, piv);
> +
> +	return err;
> +}
> +
> +/**
> + * bpf_crypto_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.
> + * @siv:	bpf_dynptr to IV data and state 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_decrypt(struct bpf_crypto_ctx *ctx,
> +				   const struct bpf_dynptr_kern *src,
> +				   struct bpf_dynptr_kern *dst,
> +				   struct bpf_dynptr_kern *siv)
> +{
> +	return bpf_crypto_crypt(ctx, src, dst, siv, true);
> +}
> +
> +/**
> + * bpf_crypto_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.
> + * @siv:		bpf_dynptr to IV data and state 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_encrypt(struct bpf_crypto_ctx *ctx,
> +				   const struct bpf_dynptr_kern *src,
> +				   struct bpf_dynptr_kern *dst,
> +				   struct bpf_dynptr_kern *siv)
> +{
> +	return bpf_crypto_crypt(ctx, src, dst, siv, false);
> +}
> +
> +__bpf_kfunc_end_defs();
> +
> +BTF_SET8_START(crypt_init_kfunc_btf_ids)
> +BTF_ID_FLAGS(func, bpf_crypto_ctx_create, KF_ACQUIRE | KF_RET_NULL | KF_SLEEPABLE)
> +BTF_ID_FLAGS(func, bpf_crypto_ctx_release, KF_RELEASE)
> +BTF_ID_FLAGS(func, bpf_crypto_ctx_acquire, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
> +BTF_SET8_END(crypt_init_kfunc_btf_ids)
> +
> +static const struct btf_kfunc_id_set crypt_init_kfunc_set = {
> +	.owner = THIS_MODULE,
> +	.set   = &crypt_init_kfunc_btf_ids,
> +};
> +
> +BTF_SET8_START(crypt_kfunc_btf_ids)
> +BTF_ID_FLAGS(func, bpf_crypto_decrypt, KF_RCU)
> +BTF_ID_FLAGS(func, bpf_crypto_encrypt, KF_RCU)
> +BTF_SET8_END(crypt_kfunc_btf_ids)
> +
> +static const struct btf_kfunc_id_set crypt_kfunc_set = {
> +	.owner = THIS_MODULE,
> +	.set   = &crypt_kfunc_btf_ids,
> +};
> +
> +BTF_ID_LIST(bpf_crypto_dtor_ids)
> +BTF_ID(struct, bpf_crypto_ctx)
> +BTF_ID(func, bpf_crypto_ctx_release)
> +
> +static int __init crypto_kfunc_init(void)
> +{
> +	int ret;
> +	const struct btf_id_dtor_kfunc bpf_crypto_dtors[] = {
> +		{
> +			.btf_id	      = bpf_crypto_dtor_ids[0],
> +			.kfunc_btf_id = bpf_crypto_dtor_ids[1]
> +		},
> +	};
> +
> +	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &crypt_kfunc_set);
> +	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_ACT, &crypt_kfunc_set);
> +	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &crypt_kfunc_set);
> +	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC,
> +					       &crypt_init_kfunc_set);
> +	return  ret ?: register_btf_id_dtor_kfuncs(bpf_crypto_dtors,
> +						   ARRAY_SIZE(bpf_crypto_dtors),
> +						   THIS_MODULE);
> +}
> +
> +late_initcall(crypto_kfunc_init);
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index e04ca1af8927..593adf036ec0 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -1440,7 +1440,7 @@ 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;
>   }
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 9507800026cf..74b24df05a3c 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -5265,6 +5265,7 @@ BTF_ID(struct, cgroup)
>   #endif
>   BTF_ID(struct, bpf_cpumask)
>   BTF_ID(struct, task_struct)
> +BTF_ID(struct, bpf_crypto_ctx)
>   BTF_SET_END(rcu_protected_types)
>   
>   static bool rcu_protected_object(const struct btf *btf, u32 btf_id)