lib/crypto: sha256: Consolidate into single module

Consolidate the CPU-based SHA-256 code into a single module, following
what I did with SHA-512:

- Each arch now provides a header file lib/crypto/$(SRCARCH)/sha256.h,
  replacing lib/crypto/$(SRCARCH)/sha256.c.  The header defines
  sha256_blocks() and optionally sha256_mod_init_arch().  It is included
  by lib/crypto/sha256.c, and thus the code gets built into the single
  libsha256 module, with proper inlining and dead code elimination.

- sha256_blocks_generic() is moved from lib/crypto/sha256-generic.c into
  lib/crypto/sha256.c.  It's now a static function marked with
  __maybe_unused, so the compiler automatically eliminates it in any
  cases where it's not used.

- Whether arch-optimized SHA-256 is buildable is now controlled
  centrally by lib/crypto/Kconfig instead of by
  lib/crypto/$(SRCARCH)/Kconfig.  The conditions for enabling it remain
  the same as before, and it remains enabled by default.

- Any additional arch-specific translation units for the optimized
  SHA-256 code (such as assembly files) are now compiled by
  lib/crypto/Makefile instead of lib/crypto/$(SRCARCH)/Makefile.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250630160645.3198-13-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

3 files changed, 9 insertions, 32 deletions

diff --git a/lib/crypto/arm/Kconfig b/lib/crypto/arm/Kconfig
index 9f3ff30f4032..e8444fd0aae3 100644
--- a/lib/crypto/arm/Kconfig
+++ b/lib/crypto/arm/Kconfig
@@ -22,9 +22,3 @@ config CRYPTO_POLY1305_ARM
 	tristate
 	default CRYPTO_LIB_POLY1305
 	select CRYPTO_ARCH_HAVE_LIB_POLY1305
-
-config CRYPTO_SHA256_ARM
-	tristate
-	depends on !CPU_V7M
-	default CRYPTO_LIB_SHA256
-	select CRYPTO_ARCH_HAVE_LIB_SHA256
diff --git a/lib/crypto/arm/Makefile b/lib/crypto/arm/Makefile
index 431f77c3ff6f..4c042a4c77ed 100644
--- a/lib/crypto/arm/Makefile
+++ b/lib/crypto/arm/Makefile
@@ -10,17 +10,13 @@ chacha-neon-$(CONFIG_KERNEL_MODE_NEON) += chacha-neon-core.o
 obj-$(CONFIG_CRYPTO_POLY1305_ARM) += poly1305-arm.o
 poly1305-arm-y := poly1305-core.o poly1305-glue.o
 
-obj-$(CONFIG_CRYPTO_SHA256_ARM) += sha256-arm.o
-sha256-arm-y := sha256.o sha256-core.o
-sha256-arm-$(CONFIG_KERNEL_MODE_NEON) += sha256-ce.o
-
 quiet_cmd_perl = PERL    $@
       cmd_perl = $(PERL) $(<) > $(@)
 
 $(obj)/%-core.S: $(src)/%-armv4.pl
 	$(call cmd,perl)
 
-clean-files += poly1305-core.S sha256-core.S
+clean-files += poly1305-core.S
 
 aflags-thumb2-$(CONFIG_THUMB2_KERNEL)  := -U__thumb2__ -D__thumb2__=1
 
@@ -28,5 +24,3 @@ aflags-thumb2-$(CONFIG_THUMB2_KERNEL)  := -U__thumb2__ -D__thumb2__=1
 poly1305-aflags-$(CONFIG_CPU_V7) := -U__LINUX_ARM_ARCH__ -D__LINUX_ARM_ARCH__=5
 poly1305-aflags-$(CONFIG_KERNEL_MODE_NEON) := -U__LINUX_ARM_ARCH__ -D__LINUX_ARM_ARCH__=7
 AFLAGS_poly1305-core.o += $(poly1305-aflags-y) $(aflags-thumb2-y)
-
-AFLAGS_sha256-core.o += $(aflags-thumb2-y)
diff --git a/lib/crypto/arm/sha256.c b/lib/crypto/arm/sha256.h
index 27181be0aa92..da75cbdc51d4 100644
--- a/lib/crypto/arm/sha256.c
+++ b/lib/crypto/arm/sha256.h
@@ -1,14 +1,11 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
+/* SPDX-License-Identifier: GPL-2.0-or-later */
 /*
  * SHA-256 optimized for ARM
  *
  * Copyright 2025 Google LLC
  */
 #include <asm/neon.h>
-#include <crypto/internal/sha2.h>
 #include <crypto/internal/simd.h>
-#include <linux/kernel.h>
-#include <linux/module.h>
 
 asmlinkage void sha256_block_data_order(struct sha256_block_state *state,
 					const u8 *data, size_t nblocks);
@@ -20,8 +17,8 @@ asmlinkage void sha256_ce_transform(struct sha256_block_state *state,
 static __ro_after_init DEFINE_STATIC_KEY_FALSE(have_neon);
 static __ro_after_init DEFINE_STATIC_KEY_FALSE(have_ce);
 
-void sha256_blocks_arch(struct sha256_block_state *state,
-			const u8 *data, size_t nblocks)
+static void sha256_blocks(struct sha256_block_state *state,
+			  const u8 *data, size_t nblocks)
 {
 	if (IS_ENABLED(CONFIG_KERNEL_MODE_NEON) &&
 	    static_branch_likely(&have_neon) && crypto_simd_usable()) {
@@ -35,23 +32,15 @@ void sha256_blocks_arch(struct sha256_block_state *state,
 		sha256_block_data_order(state, data, nblocks);
 	}
 }
-EXPORT_SYMBOL_GPL(sha256_blocks_arch);
 
-static int __init sha256_arm_mod_init(void)
+#ifdef CONFIG_KERNEL_MODE_NEON
+#define sha256_mod_init_arch sha256_mod_init_arch
+static inline void sha256_mod_init_arch(void)
 {
-	if (IS_ENABLED(CONFIG_KERNEL_MODE_NEON) && (elf_hwcap & HWCAP_NEON)) {
+	if (elf_hwcap & HWCAP_NEON) {
 		static_branch_enable(&have_neon);
 		if (elf_hwcap2 & HWCAP2_SHA2)
 			static_branch_enable(&have_ce);
 	}
-	return 0;
 }
-subsys_initcall(sha256_arm_mod_init);
-
-static void __exit sha256_arm_mod_exit(void)
-{
-}
-module_exit(sha256_arm_mod_exit);
-
-MODULE_LICENSE("GPL");
-MODULE_DESCRIPTION("SHA-256 optimized for ARM");
+#endif /* CONFIG_KERNEL_MODE_NEON */