crypto: x86/curve25519 - Remove unused kpp support

Curve25519 is used only via the library API, not the crypto_kpp API.  In
preparation for removing the unused crypto_kpp API for Curve25519,
remove the unused "curve25519-x86" kpp algorithm.

Note that the underlying x86_64 optimized Curve25519 code remains fully
supported and accessible via the library API.

It's also worth noting that even if the kpp support for Curve25519 comes
back later, there is no need for arch-specific kpp glue code like this,
as a single kpp algorithm that wraps the library API is sufficient.

Link: https://lore.kernel.org/r/20250906213523.84915-5-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

2 files changed, 1 insertions, 98 deletions

diff --git a/arch/x86/crypto/Kconfig b/arch/x86/crypto/Kconfig
index 94016c60561e..6a895a571b00 100644
--- a/arch/x86/crypto/Kconfig
+++ b/arch/x86/crypto/Kconfig
@@ -5,7 +5,6 @@ menu "Accelerated Cryptographic Algorithms for CPU (x86)"
 config CRYPTO_CURVE25519_X86
 	tristate
 	depends on 64BIT
-	select CRYPTO_KPP
 	select CRYPTO_LIB_CURVE25519_GENERIC
 	select CRYPTO_ARCH_HAVE_LIB_CURVE25519
 	default CRYPTO_LIB_CURVE25519_INTERNAL
diff --git a/arch/x86/crypto/curve25519-x86_64.c b/arch/x86/crypto/curve25519-x86_64.c
index d587f05c3c8c..ab91368284a4 100644
--- a/arch/x86/crypto/curve25519-x86_64.c
+++ b/arch/x86/crypto/curve25519-x86_64.c
@@ -5,14 +5,12 @@
  */
 
 #include <crypto/curve25519.h>
-#include <crypto/internal/kpp.h>
 
 #include <linux/export.h>
 #include <linux/types.h>
 #include <linux/jump_label.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
-#include <linux/scatterlist.h>
 
 #include <asm/cpufeature.h>
 #include <asm/processor.h>
@@ -1613,114 +1611,20 @@ void curve25519_base_arch(u8 pub[CURVE25519_KEY_SIZE],
 }
 EXPORT_SYMBOL(curve25519_base_arch);
 
-static int curve25519_set_secret(struct crypto_kpp *tfm, const void *buf,
-				 unsigned int len)
-{
-	u8 *secret = kpp_tfm_ctx(tfm);
-
-	if (!len)
-		curve25519_generate_secret(secret);
-	else if (len == CURVE25519_KEY_SIZE &&
-		 crypto_memneq(buf, curve25519_null_point, CURVE25519_KEY_SIZE))
-		memcpy(secret, buf, CURVE25519_KEY_SIZE);
-	else
-		return -EINVAL;
-	return 0;
-}
-
-static int curve25519_generate_public_key(struct kpp_request *req)
-{
-	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
-	const u8 *secret = kpp_tfm_ctx(tfm);
-	u8 buf[CURVE25519_KEY_SIZE];
-	int copied, nbytes;
-
-	if (req->src)
-		return -EINVAL;
-
-	curve25519_base_arch(buf, secret);
-
-	/* might want less than we've got */
-	nbytes = min_t(size_t, CURVE25519_KEY_SIZE, req->dst_len);
-	copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
-								nbytes),
-				     buf, nbytes);
-	if (copied != nbytes)
-		return -EINVAL;
-	return 0;
-}
-
-static int curve25519_compute_shared_secret(struct kpp_request *req)
-{
-	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
-	const u8 *secret = kpp_tfm_ctx(tfm);
-	u8 public_key[CURVE25519_KEY_SIZE];
-	u8 buf[CURVE25519_KEY_SIZE];
-	int copied, nbytes;
-
-	if (!req->src)
-		return -EINVAL;
-
-	copied = sg_copy_to_buffer(req->src,
-				   sg_nents_for_len(req->src,
-						    CURVE25519_KEY_SIZE),
-				   public_key, CURVE25519_KEY_SIZE);
-	if (copied != CURVE25519_KEY_SIZE)
-		return -EINVAL;
-
-	curve25519_arch(buf, secret, public_key);
-
-	/* might want less than we've got */
-	nbytes = min_t(size_t, CURVE25519_KEY_SIZE, req->dst_len);
-	copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
-								nbytes),
-				     buf, nbytes);
-	if (copied != nbytes)
-		return -EINVAL;
-	return 0;
-}
-
-static unsigned int curve25519_max_size(struct crypto_kpp *tfm)
-{
-	return CURVE25519_KEY_SIZE;
-}
-
-static struct kpp_alg curve25519_alg = {
-	.base.cra_name		= "curve25519",
-	.base.cra_driver_name	= "curve25519-x86",
-	.base.cra_priority	= 200,
-	.base.cra_module	= THIS_MODULE,
-	.base.cra_ctxsize	= CURVE25519_KEY_SIZE,
-
-	.set_secret		= curve25519_set_secret,
-	.generate_public_key	= curve25519_generate_public_key,
-	.compute_shared_secret	= curve25519_compute_shared_secret,
-	.max_size		= curve25519_max_size,
-};
-
-
 static int __init curve25519_mod_init(void)
 {
 	if (boot_cpu_has(X86_FEATURE_BMI2) && boot_cpu_has(X86_FEATURE_ADX))
 		static_branch_enable(&curve25519_use_bmi2_adx);
-	else
-		return 0;
-	return IS_REACHABLE(CONFIG_CRYPTO_KPP) ?
-		crypto_register_kpp(&curve25519_alg) : 0;
+	return 0;
 }
 
 static void __exit curve25519_mod_exit(void)
 {
-	if (IS_REACHABLE(CONFIG_CRYPTO_KPP) &&
-	    static_branch_likely(&curve25519_use_bmi2_adx))
-		crypto_unregister_kpp(&curve25519_alg);
 }
 
 module_init(curve25519_mod_init);
 module_exit(curve25519_mod_exit);
 
-MODULE_ALIAS_CRYPTO("curve25519");
-MODULE_ALIAS_CRYPTO("curve25519-x86");
 MODULE_DESCRIPTION("Curve25519 algorithm, ADX optimized");
 MODULE_LICENSE("GPL v2");
 MODULE_AUTHOR("Jason A. Donenfeld <Jason@zx2c4.com>");