[PATCH bpf-next v4 5/6] bpf: Add ECDSA signature verification kfuncs

Daniel Hodges
2026-01-05T17:44:16Z

Add support for ECDSA signature verification in BPF programs through
the unified bpf_crypto_ctx API.

Changes:
- Add enum bpf_crypto_type_id for efficient type checking
- Update all crypto type modules to set type_id field
- Implement bpf_ecdsa_verify() for signature verification
- Add bpf_ecdsa_keysize(), bpf_ecdsa_digestsize(), bpf_ecdsa_maxsize()
helper functions for querying context properties
- Add type_id checks in all ECDSA kfuncs for type safety
- Register ECDSA kfuncs for SCHED_CLS and XDP program types

ECDSA contexts are created using bpf_crypto_ctx_create() with
type="sig" and appropriate algorithm (e.g., "p1363(ecdsa-nist-p256)").
The public key is passed via the key/key_len fields in bpf_crypto_params.

This enables BPF programs to perform cryptographic signature verification
for use cases such as packet authentication and content validation.

Signed-off-by: Daniel Hodges <git@danielhodges.dev>
---
crypto/bpf_crypto_shash.c | 1 +
crypto/bpf_crypto_sig.c | 1 +
crypto/bpf_crypto_skcipher.c | 1 +
include/linux/bpf_crypto.h | 7 +++
kernel/bpf/crypto.c | 115 +++++++++++++++++++++++++++++++++++
5 files changed, 125 insertions(+)

diff --git a/crypto/bpf_crypto_shash.c b/crypto/bpf_crypto_shash.c
index 95c178ec0ce8..6e9b0d757ec9 100644
--- a/crypto/bpf_crypto_shash.c
+++ b/crypto/bpf_crypto_shash.c
@@ -74,6 +74,7 @@ static const struct bpf_crypto_type bpf_crypto_shash_type = {
.digestsize = bpf_crypto_shash_digestsize,
.get_flags = bpf_crypto_shash_get_flags,
.owner = THIS_MODULE,
+ .type_id = BPF_CRYPTO_TYPE_HASH,
.name = "hash",
};

diff --git a/crypto/bpf_crypto_sig.c b/crypto/bpf_crypto_sig.c
index ad0d3810df8e..c6e67338cd40 100644
--- a/crypto/bpf_crypto_sig.c
+++ b/crypto/bpf_crypto_sig.c
@@ -38,6 +38,7 @@ static const struct bpf_crypto_type bpf_crypto_sig_type = {
.get_flags = bpf_crypto_sig_get_flags,
.setkey = bpf_crypto_sig_setkey,
.owner = THIS_MODULE,
+ .type_id = BPF_CRYPTO_TYPE_SIG,
.name = "sig",
};

diff --git a/crypto/bpf_crypto_skcipher.c b/crypto/bpf_crypto_skcipher.c
index a88798d3e8c8..79d310fbcc48 100644
--- a/crypto/bpf_crypto_skcipher.c
+++ b/crypto/bpf_crypto_skcipher.c
@@ -63,6 +63,7 @@ static const struct bpf_crypto_type bpf_crypto_lskcipher_type = {
.statesize = bpf_crypto_lskcipher_statesize,
.get_flags = bpf_crypto_lskcipher_get_flags,
.owner = THIS_MODULE,
+ .type_id = BPF_CRYPTO_TYPE_SKCIPHER,
.name = "skcipher",
};

diff --git a/include/linux/bpf_crypto.h b/include/linux/bpf_crypto.h
index c84371cc4e47..cf2c66f9782b 100644
--- a/include/linux/bpf_crypto.h
+++ b/include/linux/bpf_crypto.h
@@ -3,6 +3,12 @@
#ifndef _BPF_CRYPTO_H
#define _BPF_CRYPTO_H

+enum bpf_crypto_type_id {
+ BPF_CRYPTO_TYPE_SKCIPHER = 1,
+ BPF_CRYPTO_TYPE_HASH,
+ BPF_CRYPTO_TYPE_SIG,
+};
+
struct bpf_crypto_type {
void *(*alloc_tfm)(const char *algo);
void (*free_tfm)(void *tfm);
@@ -17,6 +23,7 @@ struct bpf_crypto_type {
unsigned int (*digestsize)(void *tfm);
u32 (*get_flags)(void *tfm);
struct module *owner;
+ enum bpf_crypto_type_id type_id;
char name[14];
};

diff --git a/kernel/bpf/crypto.c b/kernel/bpf/crypto.c
index f593e7910d3d..3c57a8c31ea2 100644
--- a/kernel/bpf/crypto.c
+++ b/kernel/bpf/crypto.c
@@ -9,6 +9,7 @@
#include <linux/scatterlist.h>
#include <linux/skbuff.h>
#include <crypto/skcipher.h>
+#include <crypto/sig.h>

struct bpf_crypto_type_list {
const struct bpf_crypto_type *type;
@@ -57,6 +58,7 @@ struct bpf_crypto_ctx {
refcount_t usage;
};

+
int bpf_crypto_register_type(const struct bpf_crypto_type *type)
{
struct bpf_crypto_type_list *node;
@@ -400,6 +402,109 @@ __bpf_kfunc int bpf_crypto_hash(struct bpf_crypto_ctx *ctx,
}
#endif /* CONFIG_CRYPTO_HASH2 */

+#if IS_ENABLED(CONFIG_CRYPTO_ECDSA)
+/**
+ * bpf_ecdsa_verify() - Verify ECDSA signature using pre-allocated context
+ * @ctx: ECDSA context created by bpf_crypto_ctx_create() with type "sig"
+ * @message: bpf_dynptr to the message hash to verify. Must be a trusted pointer.
+ * @signature: bpf_dynptr to the ECDSA signature in r || s format. Must be a trusted pointer.
+ * Must be 64 bytes for P-256, 96 for P-384, 132 for P-521
+ *
+ * Verifies an ECDSA signature using a pre-allocated context. This function
+ * does not allocate memory and can be used in non-sleepable BPF programs.
+ * Uses bpf_dynptr to ensure safe memory access without risk of page faults.
+ */
+__bpf_kfunc int bpf_ecdsa_verify(struct bpf_crypto_ctx *ctx,
+ const struct bpf_dynptr *message,
+ const struct bpf_dynptr *signature)
+{
+ const struct bpf_dynptr_kern *msg_kern = (struct bpf_dynptr_kern *)message;
+ const struct bpf_dynptr_kern *sig_kern = (struct bpf_dynptr_kern *)signature;
+ struct crypto_sig *sig_tfm;
+ const u8 *msg_ptr, *sig_ptr;
+ u32 msg_len, sig_len;
+
+ if (!ctx)
+ return -EINVAL;
+
+ if (ctx->type->type_id != BPF_CRYPTO_TYPE_SIG)
+ return -EINVAL;
+
+ msg_len = __bpf_dynptr_size(msg_kern);
+ sig_len = __bpf_dynptr_size(sig_kern);
+
+ if (msg_len == 0 || sig_len == 0)
+ return -EINVAL;
+
+ msg_ptr = __bpf_dynptr_data(msg_kern, msg_len);
+ if (!msg_ptr)
+ return -EINVAL;
+
+ sig_ptr = __bpf_dynptr_data(sig_kern, sig_len);
+ if (!sig_ptr)
+ return -EINVAL;
+
+ sig_tfm = (struct crypto_sig *)ctx->tfm;
+ return crypto_sig_verify(sig_tfm, sig_ptr, sig_len, msg_ptr, msg_len);
+}
+
+/**
+ * bpf_ecdsa_keysize() - Get the key size for ECDSA context
+ * @ctx: ECDSA context
+ *
+ * Returns: Key size in bits, or negative error code on failure
+ */
+__bpf_kfunc int bpf_ecdsa_keysize(struct bpf_crypto_ctx *ctx)
+{
+ struct crypto_sig *sig_tfm;
+
+ if (!ctx)
+ return -EINVAL;
+
+ if (ctx->type->type_id != BPF_CRYPTO_TYPE_SIG)
+ return -EINVAL;
+
+ sig_tfm = (struct crypto_sig *)ctx->tfm;
+ return crypto_sig_keysize(sig_tfm);
+}
+
+/**
+ * bpf_ecdsa_digestsize() - Get the maximum digest size for ECDSA context
+ * @ctx: ECDSA context
+ */
+__bpf_kfunc int bpf_ecdsa_digestsize(struct bpf_crypto_ctx *ctx)
+{
+ struct crypto_sig *sig_tfm;
+
+ if (!ctx)
+ return -EINVAL;
+
+ if (ctx->type->type_id != BPF_CRYPTO_TYPE_SIG)
+ return -EINVAL;
+
+ sig_tfm = (struct crypto_sig *)ctx->tfm;
+ return crypto_sig_digestsize(sig_tfm);
+}
+
+/**
+ * bpf_ecdsa_maxsize() - Get the maximum signature size for ECDSA context
+ * @ctx: ECDSA context
+ */
+__bpf_kfunc int bpf_ecdsa_maxsize(struct bpf_crypto_ctx *ctx)
+{
+ struct crypto_sig *sig_tfm;
+
+ if (!ctx)
+ return -EINVAL;
+
+ if (ctx->type->type_id != BPF_CRYPTO_TYPE_SIG)
+ return -EINVAL;
+
+ sig_tfm = (struct crypto_sig *)ctx->tfm;
+ return crypto_sig_maxsize(sig_tfm);
+}
+#endif /* CONFIG_CRYPTO_ECDSA */
+
__bpf_kfunc_end_defs();

BTF_KFUNCS_START(crypt_init_kfunc_btf_ids)
@@ -419,6 +524,12 @@ BTF_ID_FLAGS(func, bpf_crypto_encrypt, KF_RCU)
#if IS_ENABLED(CONFIG_CRYPTO_HASH2)
BTF_ID_FLAGS(func, bpf_crypto_hash, KF_RCU)
#endif
+#if IS_ENABLED(CONFIG_CRYPTO_ECDSA)
+BTF_ID_FLAGS(func, bpf_ecdsa_verify, KF_RCU)
+BTF_ID_FLAGS(func, bpf_ecdsa_keysize, 0)
+BTF_ID_FLAGS(func, bpf_ecdsa_digestsize, 0)
+BTF_ID_FLAGS(func, bpf_ecdsa_maxsize, 0)
+#endif
BTF_KFUNCS_END(crypt_kfunc_btf_ids)

static const struct btf_kfunc_id_set crypt_kfunc_set = {
@@ -447,6 +558,10 @@ static int __init crypto_kfunc_init(void)
ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &crypt_kfunc_set);
ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL,
&crypt_init_kfunc_set);
+ ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS,
+ &crypt_init_kfunc_set);
+ ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP,
+ &crypt_init_kfunc_set);
return ret ?: register_btf_id_dtor_kfuncs(bpf_crypto_dtors,
ARRAY_SIZE(bpf_crypto_dtors),
THIS_MODULE);
--
2.51.0