bpf: make common crypto API for TC/XDP programs

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 <vadfed@meta.com>
Link: https://lore.kernel.org/r/20240422225024.2847039-2-vadfed@meta.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

include/linux/bpf.h

@@ -1275,6 +1275,7 @@ 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);

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 */

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

kernel/bpf/crypto.c

@@ -0,0 +1,385 @@
+// 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.
+ * @reserved:	Reserved member, will be reused for more options in future
+ *		Values:
+ *		  0
+ * @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];
+	u8 reserved[2];
+	char algo[128];
+	u8 key[256];
+	u32 key_len;
+	u32 authsize;
+};
+
+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.
+ * @siv_len:    Size of IV and state storage for cipher
+ * @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.
+ * @params__sz:	size of steuct bpf_crypto_params usef by bpf program
+ * @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, u32 params__sz,
+		      int *err)
+{
+	const struct bpf_crypto_type *type;
+	struct bpf_crypto_ctx *ctx;
+
+	if (!params || params->reserved[0] || params->reserved[1] ||
+	    params__sz != sizeof(struct bpf_crypto_params)) {
+		*err = -EINVAL;
+		return NULL;
+	}
+
+	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->key_len || 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_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, its memory
+ * will be released.
+ */
+__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,
+			    const 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;
+	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,
+				   const struct bpf_dynptr_kern *dst,
+				   const 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,
+				   const struct bpf_dynptr_kern *dst,
+				   const struct bpf_dynptr_kern *siv)
+{
+	return bpf_crypto_crypt(ctx, src, dst, siv, false);
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_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_KFUNCS_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_KFUNCS_START(crypt_kfunc_btf_ids)
+BTF_ID_FLAGS(func, bpf_crypto_decrypt, KF_RCU)
+BTF_ID_FLAGS(func, bpf_crypto_encrypt, KF_RCU)
+BTF_KFUNCS_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_SYSCALL,
+					       &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);

kernel/bpf/helpers.c

@@ -1583,7 +1583,7 @@ 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;
 }

kernel/bpf/verifier.c

@@ -5310,6 +5310,7 @@ BTF_ID(struct, cgroup)
 BTF_ID(struct, bpf_cpumask)
 #endif
 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)