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

Vadim Fedorenko
2023-10-26T02:00:08Z

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@meta.com>
---
include/linux/bpf.h | 1 +
kernel/bpf/Makefile | 3 +
kernel/bpf/crypto.c | 278 ++++++++++++++++++++++++++++++++++++++++++
kernel/bpf/helpers.c | 2 +-
kernel/bpf/verifier.c | 1 +
5 files changed, 284 insertions(+), 1 deletion(-)
create mode 100644 kernel/bpf/crypto.c

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index d3c51a507508..17145738f176 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1222,6 +1222,7 @@ enum bpf_dynptr_type {

int bpf_dynptr_check_size(u32 size);
u32 __bpf_dynptr_size(const struct bpf_dynptr_kern *ptr);
+enum bpf_dynptr_type bpf_dynptr_get_type(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..f7803a5591b0
--- /dev/null
+++ b/kernel/bpf/crypto.c
@@ -0,0 +1,278 @@
+// 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;
+};
+
+static struct bpf_mem_alloc bpf_crypto_ctx_ma;
+
+__diag_push();
+__diag_ignore_all("-Wmissing-prototypes",
+ "Global kfuncs as their definitions will be in BTF");
+
+/**
+ * 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 *algo, const struct bpf_dynptr_kern *key,
+ int *err)
+{
+ struct bpf_crypto_skcipher_ctx *ctx;
+
+ if (__bpf_dynptr_size(algo) > CRYPTO_MAX_ALG_NAME) {
+ *err = -EINVAL;
+ return NULL;
+ }
+
+ if (!crypto_has_skcipher(algo->data, CRYPTO_ALG_TYPE_SKCIPHER, CRYPTO_ALG_TYPE_MASK)) {
+ *err = -EOPNOTSUPP;
+ return NULL;
+ }
+
+ ctx = bpf_mem_cache_alloc(&bpf_crypto_ctx_ma);
+ if (!ctx) {
+ *err = -ENOMEM;
+ return NULL;
+ }
+
+ memset(ctx, 0, sizeof(*ctx));
+
+ ctx->tfm = crypto_alloc_sync_skcipher(algo->data, 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->data, __bpf_dynptr_size(key));
+ if (*err)
+ goto err;
+
+ refcount_set(&ctx->usage, 1);
+
+ return ctx;
+err:
+ if (ctx->tfm)
+ crypto_free_sync_skcipher(ctx->tfm);
+ bpf_mem_cache_free(&bpf_crypto_ctx_ma, 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);
+ migrate_disable();
+ bpf_mem_cache_free(&bpf_crypto_ctx_ma, ctx);
+ migrate_enable();
+}
+
+/**
+ * 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 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;
+ }
+}
+
+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_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 = bpf_mem_alloc_init(&bpf_crypto_ctx_ma, sizeof(struct bpf_crypto_skcipher_ctx), false);
+ ret = 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..0c2a10ff5dfd 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -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