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, 8 insertions, 31 deletions

diff --git a/lib/crypto/x86/Kconfig b/lib/crypto/x86/Kconfig
index e344579db3d8..546fe2afe0b5 100644
--- a/lib/crypto/x86/Kconfig
+++ b/lib/crypto/x86/Kconfig
@@ -24,10 +24,3 @@ config CRYPTO_POLY1305_X86_64
 	depends on 64BIT
 	default CRYPTO_LIB_POLY1305
 	select CRYPTO_ARCH_HAVE_LIB_POLY1305
-
-config CRYPTO_SHA256_X86_64
-	tristate
-	depends on 64BIT
-	default CRYPTO_LIB_SHA256
-	select CRYPTO_ARCH_HAVE_LIB_SHA256
-	select CRYPTO_LIB_SHA256_GENERIC
diff --git a/lib/crypto/x86/Makefile b/lib/crypto/x86/Makefile
index abceca3d31c0..c2ff8c5f1046 100644
--- a/lib/crypto/x86/Makefile
+++ b/lib/crypto/x86/Makefile
@@ -10,9 +10,6 @@ obj-$(CONFIG_CRYPTO_POLY1305_X86_64) += poly1305-x86_64.o
 poly1305-x86_64-y := poly1305-x86_64-cryptogams.o poly1305_glue.o
 targets += poly1305-x86_64-cryptogams.S
 
-obj-$(CONFIG_CRYPTO_SHA256_X86_64) += sha256-x86_64.o
-sha256-x86_64-y := sha256.o sha256-ssse3-asm.o sha256-avx-asm.o sha256-avx2-asm.o sha256-ni-asm.o
-
 quiet_cmd_perlasm = PERLASM $@
       cmd_perlasm = $(PERL) $< > $@
 
diff --git a/lib/crypto/x86/sha256.c b/lib/crypto/x86/sha256.h
index 9ee38d2b3d57..3b5456c222ba 100644
--- a/lib/crypto/x86/sha256.c
+++ b/lib/crypto/x86/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 x86_64
  *
  * Copyright 2025 Google LLC
  */
 #include <asm/fpu/api.h>
-#include <crypto/internal/sha2.h>
 #include <crypto/internal/simd.h>
-#include <linux/kernel.h>
-#include <linux/module.h>
 #include <linux/static_call.h>
 
 asmlinkage void sha256_transform_ssse3(struct sha256_block_state *state,
@@ -24,8 +21,8 @@ static __ro_after_init DEFINE_STATIC_KEY_FALSE(have_sha256_x86);
 
 DEFINE_STATIC_CALL(sha256_blocks_x86, sha256_transform_ssse3);
 
-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 (static_branch_likely(&have_sha256_x86) && crypto_simd_usable()) {
 		kernel_fpu_begin();
@@ -35,14 +32,14 @@ void sha256_blocks_arch(struct sha256_block_state *state,
 		sha256_blocks_generic(state, data, nblocks);
 	}
 }
-EXPORT_SYMBOL_GPL(sha256_blocks_arch);
 
-static int __init sha256_x86_mod_init(void)
+#define sha256_mod_init_arch sha256_mod_init_arch
+static inline void sha256_mod_init_arch(void)
 {
 	if (boot_cpu_has(X86_FEATURE_SHA_NI)) {
 		static_call_update(sha256_blocks_x86, sha256_ni_transform);
-	} else if (cpu_has_xfeatures(XFEATURE_MASK_SSE |
-				     XFEATURE_MASK_YMM, NULL) &&
+	} else if (cpu_has_xfeatures(XFEATURE_MASK_SSE | XFEATURE_MASK_YMM,
+				     NULL) &&
 		   boot_cpu_has(X86_FEATURE_AVX)) {
 		if (boot_cpu_has(X86_FEATURE_AVX2) &&
 		    boot_cpu_has(X86_FEATURE_BMI2))
@@ -52,17 +49,7 @@ static int __init sha256_x86_mod_init(void)
 			static_call_update(sha256_blocks_x86,
 					   sha256_transform_avx);
 	} else if (!boot_cpu_has(X86_FEATURE_SSSE3)) {
-		return 0;
+		return;
 	}
 	static_branch_enable(&have_sha256_x86);
-	return 0;
 }
-subsys_initcall(sha256_x86_mod_init);
-
-static void __exit sha256_x86_mod_exit(void)
-{
-}
-module_exit(sha256_x86_mod_exit);
-
-MODULE_LICENSE("GPL");
-MODULE_DESCRIPTION("SHA-256 optimized for x86_64");