[PATCH bpf-next v2 1/5] crypto: Add BPF hash algorithm type registration module

Daniel Hodges
2025-12-05T17:40:26Z

Add bpf_crypto_shash module that registers a hash type with the BPF
crypto infrastructure, enabling BPF programs to access kernel hash
algorithms through a unified interface.

Update the bpf_crypto_type interface with hash-specific callbacks:
- alloc_tfm: Allocates crypto_shash context with proper descriptor size
- free_tfm: Releases hash transform and context memory
- has_algo: Checks algorithm availability via crypto_has_shash()
- hash: Performs single-shot hashing via crypto_shash_digest()
- digestsize: Returns the output size for the hash algorithm
- get_flags: Exposes transform flags to BPF programs

Update bpf_shash_ctx to contain crypto_shash transform and shash_desc
descriptor to accommodate algorithm-specific descriptor requirements.

Signed-off-by: Daniel Hodges <git@danielhodges.dev>
---
crypto/Makefile | 3 ++
crypto/bpf_crypto_shash.c | 94 +++++++++++++++++++++++++++++++++++++++
2 files changed, 97 insertions(+)
create mode 100644 crypto/bpf_crypto_shash.c

diff --git a/crypto/Makefile b/crypto/Makefile
index 16a35649dd91..853dff375906 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -30,6 +30,9 @@ obj-$(CONFIG_CRYPTO_ECHAINIV) += echainiv.o
crypto_hash-y += ahash.o
crypto_hash-y += shash.o
obj-$(CONFIG_CRYPTO_HASH2) += crypto_hash.o
+ifeq ($(CONFIG_BPF_SYSCALL),y)
+obj-$(CONFIG_CRYPTO_HASH2) += bpf_crypto_shash.o
+endif

obj-$(CONFIG_CRYPTO_AKCIPHER2) += akcipher.o
obj-$(CONFIG_CRYPTO_SIG2) += sig.o
diff --git a/crypto/bpf_crypto_shash.c b/crypto/bpf_crypto_shash.c
new file mode 100644
index 000000000000..39032e7dd602
--- /dev/null
+++ b/crypto/bpf_crypto_shash.c
@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/types.h>
+#include <linux/module.h>
+#include <linux/bpf_crypto.h>
+#include <crypto/hash.h>
+
+struct bpf_shash_ctx {
+ struct crypto_shash *tfm;
+ struct shash_desc desc;
+};
+
+static void *bpf_crypto_shash_alloc_tfm(const char *algo)
+{
+ struct bpf_shash_ctx *ctx;
+ struct crypto_shash *tfm;
+
+ tfm = crypto_alloc_shash(algo, 0, 0);
+ if (IS_ERR(tfm))
+ return tfm;
+
+ ctx = kzalloc(sizeof(*ctx) + crypto_shash_descsize(tfm), GFP_KERNEL);
+ if (!ctx) {
+ crypto_free_shash(tfm);
+ return ERR_PTR(-ENOMEM);
+ }
+
+ ctx->tfm = tfm;
+ ctx->desc.tfm = tfm;
+
+ return ctx;
+}
+
+static void bpf_crypto_shash_free_tfm(void *tfm)
+{
+ struct bpf_shash_ctx *ctx = tfm;
+
+ crypto_free_shash(ctx->tfm);
+ kfree(ctx);
+}
+
+static int bpf_crypto_shash_has_algo(const char *algo)
+{
+ return crypto_has_shash(algo, 0, 0);
+}
+
+static int bpf_crypto_shash_hash(void *tfm, const u8 *data, u8 *out,
+ unsigned int len)
+{
+ struct bpf_shash_ctx *ctx = tfm;
+
+ return crypto_shash_digest(&ctx->desc, data, len, out);
+}
+
+static unsigned int bpf_crypto_shash_digestsize(void *tfm)
+{
+ struct bpf_shash_ctx *ctx = tfm;
+
+ return crypto_shash_digestsize(ctx->tfm);
+}
+
+static u32 bpf_crypto_shash_get_flags(void *tfm)
+{
+ struct bpf_shash_ctx *ctx = tfm;
+
+ return crypto_shash_get_flags(ctx->tfm);
+}
+
+static const struct bpf_crypto_type bpf_crypto_shash_type = {
+ .alloc_tfm = bpf_crypto_shash_alloc_tfm,
+ .free_tfm = bpf_crypto_shash_free_tfm,
+ .has_algo = bpf_crypto_shash_has_algo,
+ .hash = bpf_crypto_shash_hash,
+ .digestsize = bpf_crypto_shash_digestsize,
+ .get_flags = bpf_crypto_shash_get_flags,
+ .owner = THIS_MODULE,
+ .name = "hash",
+};
+
+static int __init bpf_crypto_shash_init(void)
+{
+ return bpf_crypto_register_type(&bpf_crypto_shash_type);
+}
+
+static void __exit bpf_crypto_shash_exit(void)
+{
+ int err = bpf_crypto_unregister_type(&bpf_crypto_shash_type);
+
+ WARN_ON_ONCE(err);
+}
+
+module_init(bpf_crypto_shash_init);
+module_exit(bpf_crypto_shash_exit);
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Hash algorithm support for BPF");
--
2.51.0