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.
Signed-off-by: Vadim Fedorenko <vadfed@xxxxxxxx>
---
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 +
kernel/bpf/Makefile | 3 +
kernel/bpf/crypto.c | 265 ++++++++++++++++++++++++++++++++++++++++++
kernel/bpf/helpers.c | 2 +-
kernel/bpf/verifier.c | 1 +
5 files changed, 271 insertions(+), 1 deletion(-)
create mode 100644 kernel/bpf/crypto.c
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 4001d11be151..77934ab7421d 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1224,6 +1224,7 @@ 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/kernel/bpf/Makefile b/kernel/bpf/Makefile
index f526b7573e97..e14b5834c477 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_SKCIPHER),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..4fe1470ad4b8
--- /dev/null
+++ b/kernel/bpf/crypto.c
@@ -0,0 +1,265 @@
+// 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;
+};
+
+__bpf_kfunc_start_defs();
+
+/**
+ * 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__str: pointer to string representation of algorithm.
+ * @pkey: bpf_dynptr which holds cipher key to do crypto.
+ * @err: integer to store error code when NULL is returned
+ */
+__bpf_kfunc struct bpf_crypto_skcipher_ctx *
+bpf_crypto_skcipher_ctx_create(const char *algo__str, const struct bpf_dynptr_kern *pkey,
+ int *err)
+{
+ struct bpf_crypto_skcipher_ctx *ctx;
+ const u8 *key;
+ u32 key_len;
+
+ if (!crypto_has_skcipher(algo__str, CRYPTO_ALG_TYPE_SKCIPHER, CRYPTO_ALG_TYPE_MASK)) {
+ *err = -EOPNOTSUPP;
+ return NULL;
+ }
+
+ key_len = __bpf_dynptr_size(pkey);
+ if (!key_len) {
+ *err = -EINVAL;
+ return NULL;
+ }
+ key = __bpf_dynptr_data(pkey, key_len);
+ if (!key) {
+ *err = -EINVAL;
+ return NULL;
+ }
+
+ ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+ if (!ctx) {
+ *err = -ENOMEM;
+ return NULL;
+ }
+
+ ctx->tfm = crypto_alloc_sync_skcipher(algo__str, 0, 0);
+ if (IS_ERR(ctx->tfm)) {
+ *err = PTR_ERR(ctx->tfm);
+ ctx->tfm = NULL;
+ goto err;
+ }
+
+ *err = crypto_sync_skcipher_setkey(ctx->tfm, key, key_len);
+ 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)
+{
+ SYNC_SKCIPHER_REQUEST_ON_STACK(req, tfm);
+ struct scatterlist sgin, sgout;
+ u32 src_len, dst_len, iv_len;
+ const u8 *psrc;
+ u8 *pdst, *piv;
+ int err;
+
+ if (crypto_sync_skcipher_get_flags(tfm) & CRYPTO_TFM_NEED_KEY)
+ return -EINVAL;
+
+ if (__bpf_dynptr_is_rdonly(dst))
+ return -EINVAL;
+
+ iv_len = __bpf_dynptr_size(iv);
+ src_len = __bpf_dynptr_size(src);
+ dst_len = __bpf_dynptr_size(dst);
+ if (!src_len || !dst_len)
+ return -EINVAL;
+
+ if (iv_len != crypto_sync_skcipher_ivsize(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 = iv_len ? __bpf_dynptr_data_rw(iv, iv_len) : NULL;
+ if (iv_len && !piv)
+ return -EINVAL;
+
+ sg_init_one(&sgin, psrc, src_len);
+ sg_init_one(&sgout, pdst, dst_len);
+
+ skcipher_request_set_sync_tfm(req, tfm);
+ skcipher_request_set_callback(req, 0, NULL, NULL);
+ skcipher_request_set_crypt(req, &sgin, &sgout, src_len, piv);
+
+ err = decrypt ? crypto_skcipher_decrypt(req) : crypto_skcipher_encrypt(req);
+ skcipher_request_zero(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,
+ 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,
+ struct bpf_dynptr_kern *iv)
+{
+ return bpf_crypto_skcipher_crypt(ctx->tfm, src, dst, iv, false);
+}
+
+__bpf_kfunc_end_defs();
+
+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 03517db5cfb3..eb6ddc7e7fdc 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1436,7 +1436,7 @@ 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 9ae6eae13471..aac46e7f22ab 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5552,6 +5552,7 @@ BTF_ID(struct, cgroup)
#endif
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
