[PATCH bpf-next v4 2/6] crypto: Add BPF signature algorithm type registration module

[Daniel Hodges <git@danielhodges.dev>]

Add a new bpf_crypto_sig module that registers signature verification
algorithms with the BPF crypto type system. This enables signature
operations (like ECDSA) to use the unified bpf_crypto_ctx structure
instead of requiring separate context types.

The module provides:
- alloc_tfm/free_tfm for crypto_sig transform lifecycle
- has_algo to check algorithm availability
- get_flags for crypto API flags

This allows ECDSA and other signature verification operations to
integrate with the existing BPF crypto infrastructure.

Signed-off-by: Daniel Hodges <git@danielhodges.dev>
---
 MAINTAINERS             |  1 +
 crypto/Makefile         |  3 +++
 crypto/bpf_crypto_sig.c | 59 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 63 insertions(+)
 create mode 100644 crypto/bpf_crypto_sig.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 05e0aee5693c..fdf451bad869 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4713,6 +4713,7 @@ M:	Vadim Fedorenko <vadim.fedorenko@linux.dev>
 L:	bpf@vger.kernel.org
 S:	Maintained
 F:	crypto/bpf_crypto_shash.c
+F:	crypto/bpf_crypto_sig.c
 F:	crypto/bpf_crypto_skcipher.c
 F:	include/linux/bpf_crypto.h
 F:	kernel/bpf/crypto.c
diff --git a/crypto/Makefile b/crypto/Makefile
index 853dff375906..c9ab98b57bc0 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -36,6 +36,9 @@ endif
 
 obj-$(CONFIG_CRYPTO_AKCIPHER2) += akcipher.o
 obj-$(CONFIG_CRYPTO_SIG2) += sig.o
+ifeq ($(CONFIG_BPF_SYSCALL),y)
+obj-$(CONFIG_CRYPTO_SIG2) += bpf_crypto_sig.o
+endif
 obj-$(CONFIG_CRYPTO_KPP2) += kpp.o
 obj-$(CONFIG_CRYPTO_HKDF) += hkdf.o
 
diff --git a/crypto/bpf_crypto_sig.c b/crypto/bpf_crypto_sig.c
new file mode 100644
index 000000000000..ad0d3810df8e
--- /dev/null
+++ b/crypto/bpf_crypto_sig.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+#include <linux/types.h>
+#include <linux/module.h>
+#include <linux/bpf_crypto.h>
+#include <linux/crypto.h>
+#include <crypto/sig.h>
+
+static void *bpf_crypto_sig_alloc_tfm(const char *algo)
+{
+	return crypto_alloc_sig(algo, 0, 0);
+}
+
+static void bpf_crypto_sig_free_tfm(void *tfm)
+{
+	crypto_free_sig(tfm);
+}
+
+static int bpf_crypto_sig_has_algo(const char *algo)
+{
+	return crypto_has_alg(algo, CRYPTO_ALG_TYPE_SIG, CRYPTO_ALG_TYPE_MASK);
+}
+
+static u32 bpf_crypto_sig_get_flags(void *tfm)
+{
+	return crypto_tfm_get_flags(crypto_sig_tfm(tfm));
+}
+
+static int bpf_crypto_sig_setkey(void *tfm, const u8 *key, unsigned int keylen)
+{
+	return crypto_sig_set_pubkey(tfm, key, keylen);
+}
+
+static const struct bpf_crypto_type bpf_crypto_sig_type = {
+	.alloc_tfm	= bpf_crypto_sig_alloc_tfm,
+	.free_tfm	= bpf_crypto_sig_free_tfm,
+	.has_algo	= bpf_crypto_sig_has_algo,
+	.get_flags	= bpf_crypto_sig_get_flags,
+	.setkey		= bpf_crypto_sig_setkey,
+	.owner		= THIS_MODULE,
+	.name		= "sig",
+};
+
+static int __init bpf_crypto_sig_init(void)
+{
+	return bpf_crypto_register_type(&bpf_crypto_sig_type);
+}
+
+static void __exit bpf_crypto_sig_exit(void)
+{
+	int err = bpf_crypto_unregister_type(&bpf_crypto_sig_type);
+
+	WARN_ON_ONCE(err);
+}
+
+module_init(bpf_crypto_sig_init);
+module_exit(bpf_crypto_sig_exit);
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Signature algorithm support for BPF");
-- 
2.51.0