Message-ID: <adf36f26-76b7-4c57-8caf-82f4bb98f017@linux.dev>
Date: Fri, 19 Apr 2024 11:57:24 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Vadim Fedorenko <vadfed@...a.com>
Cc: Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
 Jakub Kicinski <kuba@...nel.org>, Andrii Nakryiko <andrii@...nel.org>,
 Alexei Starovoitov <ast@...nel.org>, Mykola Lysenko <mykolal@...com>,
 Herbert Xu <herbert@...dor.apana.org.au>, netdev@...r.kernel.org,
 linux-crypto@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v9 1/4] bpf: make common crypto API for TC/XDP
 programs

On 4/16/24 1:40 PM, Vadim Fedorenko wrote:
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 5034c1b4ded7..acc479c13f52 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1265,6 +1265,7 @@ 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..a41e71d4e2d9
> --- /dev/null
> +++ b/include/linux/bpf_crypto.h
> @@ -0,0 +1,24 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/* Copyright (c) 2024 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 368c5d86b5b7..736bd22e5ce0 100644
> --- a/kernel/bpf/Makefile
> +++ b/kernel/bpf/Makefile
> @@ -44,6 +44,9 @@ 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..a76d80f37f55
> --- /dev/null
> +++ b/kernel/bpf/crypto.c
> @@ -0,0 +1,377 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright (c) 2024 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;
> +};
> +
> +/* BPF crypto initialization parameters struct */
> +/**
> + * struct bpf_crypto_params - BPF crypto initialization parameters structure
> + * @type:	The string of crypto operation type.
> + * @algo:	The string of algorithm to initialize.
> + * @key:	The cipher key used to init crypto algorithm.
> + * @key_len:	The length of cipher key.
> + * @authsize:	The length of authentication tag used by algorithm.
> + */
> +struct bpf_crypto_params {
> +	char type[14];
> +	char algo[128];
> +	__u8 key[256];

It should have a two byte hole here. Add
	__u8 reserved[2];

and check for 0 in bpf_crypto_ctx_create() in case it could be reused later. The 
bpf_crypto_ctx_create() should not be called very often.

> +	__u32 key_len;
> +	__u32 authsize;

I don't think there is tail padding of this struct, so should be fine.

> +} __attribute__((aligned(8)));

Does it need aligned(8) here?

> +
> +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;
> +	u32 siv_len;
> +	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.
> + * @params: pointer to struct bpf_crypto_params which contains all the
> + *          details needed to initialise crypto context.
> + * @err:    integer to store error code when NULL is returned.
> + */
> +__bpf_kfunc struct bpf_crypto_ctx *
> +bpf_crypto_ctx_create(const struct bpf_crypto_params *params, int *err)

Add a "u32 params__sz" arg in case that the params struct will have addition.
Take a look at how opts__sz is checked in nf_conntrack_bpf.c.

> +{
> +	const struct bpf_crypto_type *type;
> +	struct bpf_crypto_ctx *ctx;
> +
> +	type = bpf_crypto_get_type(params->type);
> +	if (IS_ERR(type)) {
> +		*err = PTR_ERR(type);
> +		return NULL;
> +	}
> +
> +	if (!type->has_algo(params->algo)) {
> +		*err = -EOPNOTSUPP;
> +		goto err_module_put;
> +	}
> +
> +	if (!params->authsize && type->setauthsize) {
> +		*err = -EOPNOTSUPP;
> +		goto err_module_put;
> +	}
> +
> +	if (params->authsize && !type->setauthsize) {

nit. Together with the previous "if" test, replace them with one test like:

	if (!!params->authsize ^ !!type->setauthsize) {


> +		*err = -EOPNOTSUPP;
> +		goto err_module_put;
> +	}
> +
> +	if (!params->key_len) {

Also checks "|| params->key_len > sizeof(params->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(params->algo);
> +	if (IS_ERR(ctx->tfm)) {
> +		*err = PTR_ERR(ctx->tfm);
> +		goto err_free_ctx;
> +	}
> +
> +	if (params->authsize) {
> +		*err = type->setauthsize(ctx->tfm, params->authsize);
> +		if (*err)
> +			goto err_free_tfm;
> +	}
> +
> +	*err = type->setkey(ctx->tfm, params->key, params->key_len);
> +	if (*err)
> +		goto err_free_tfm;
> +
> +	if (type->get_flags(ctx->tfm) & CRYPTO_TFM_NEED_KEY) {
> +		*err = -EINVAL;
> +		goto err_free_tfm;
> +	}
> +
> +	ctx->siv_len = type->ivsize(ctx->tfm) + type->statesize(ctx->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)
> +{
> +	if (!refcount_inc_not_zero(&ctx->usage))
> +		return NULL;
> +	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 (__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->siv_len)
> +		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;

It has been a while. I don't remember if it has already been brought up before.

The "const struct bpf_dynptr_kern *siv" here is essentially an optional pointer. 
Allowing NULL is a more intuitive usage instead of passing a 0-len dynptr. The 
verifier needs some changes to take __nullable suffix for "struct 
bpf_dynptr_kern *siv__nullable". This could be a follow up to relax the 
restriction to allow NULL and not necessary in this set.

> +	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;
> +}

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