crypto: s390/sha256 - implement library instead of shash

Instead of providing crypto_shash algorithms for the arch-optimized
SHA-256 code, instead implement the SHA-256 library.  This is much
simpler, it makes the SHA-256 library functions be arch-optimized, and
it fixes the longstanding issue where the arch-optimized SHA-256 was
disabled by default.  SHA-256 still remains available through
crypto_shash, but individual architectures no longer need to handle it.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

3 files changed, 55 insertions, 0 deletions

diff --git a/arch/s390/lib/crypto/Kconfig b/arch/s390/lib/crypto/Kconfig
index 069b355fe51a..e3f855ef4393 100644
--- a/arch/s390/lib/crypto/Kconfig
+++ b/arch/s390/lib/crypto/Kconfig
@@ -5,3 +5,9 @@ config CRYPTO_CHACHA_S390
 	default CRYPTO_LIB_CHACHA
 	select CRYPTO_LIB_CHACHA_GENERIC
 	select CRYPTO_ARCH_HAVE_LIB_CHACHA
+
+config CRYPTO_SHA256_S390
+	tristate
+	default CRYPTO_LIB_SHA256
+	select CRYPTO_ARCH_HAVE_LIB_SHA256
+	select CRYPTO_LIB_SHA256_GENERIC
diff --git a/arch/s390/lib/crypto/Makefile b/arch/s390/lib/crypto/Makefile
index 06c2cf77178e..920197967f46 100644
--- a/arch/s390/lib/crypto/Makefile
+++ b/arch/s390/lib/crypto/Makefile
@@ -2,3 +2,5 @@
 
 obj-$(CONFIG_CRYPTO_CHACHA_S390) += chacha_s390.o
 chacha_s390-y := chacha-glue.o chacha-s390.o
+
+obj-$(CONFIG_CRYPTO_SHA256_S390) += sha256.o
diff --git a/arch/s390/lib/crypto/sha256.c b/arch/s390/lib/crypto/sha256.c
new file mode 100644
index 000000000000..50c592ce7a5d
--- /dev/null
+++ b/arch/s390/lib/crypto/sha256.c
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * SHA-256 optimized using the CP Assist for Cryptographic Functions (CPACF)
+ *
+ * Copyright 2025 Google LLC
+ */
+#include <asm/cpacf.h>
+#include <crypto/internal/sha2.h>
+#include <linux/cpufeature.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+static __ro_after_init DEFINE_STATIC_KEY_FALSE(have_cpacf_sha256);
+
+void sha256_blocks_arch(u32 state[SHA256_STATE_WORDS],
+			const u8 *data, size_t nblocks)
+{
+	if (static_branch_likely(&have_cpacf_sha256))
+		cpacf_kimd(CPACF_KIMD_SHA_256, state, data,
+			   nblocks * SHA256_BLOCK_SIZE);
+	else
+		sha256_blocks_generic(state, data, nblocks);
+}
+EXPORT_SYMBOL(sha256_blocks_arch);
+
+bool sha256_is_arch_optimized(void)
+{
+	return static_key_enabled(&have_cpacf_sha256);
+}
+EXPORT_SYMBOL(sha256_is_arch_optimized);
+
+static int __init sha256_s390_mod_init(void)
+{
+	if (cpu_have_feature(S390_CPU_FEATURE_MSA) &&
+	    cpacf_query_func(CPACF_KIMD, CPACF_KIMD_SHA_256))
+		static_branch_enable(&have_cpacf_sha256);
+	return 0;
+}
+arch_initcall(sha256_s390_mod_init);
+
+static void __exit sha256_s390_mod_exit(void)
+{
+}
+module_exit(sha256_s390_mod_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("SHA-256 using the CP Assist for Cryptographic Functions (CPACF)");