From 2e8f7b170a085f0f5522f262bffe92d6ec911abb Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Thu, 4 Dec 2025 21:03:30 -0800 Subject: [PATCH] lib/crypto: blake2b: Roll up BLAKE2b round loop on 32-bit BLAKE2b has a state of 16 64-bit words. Add the message data in and there are 32 64-bit words. With the current code where all the rounds are unrolled to enable constant-folding of the blake2b_sigma values, this results in a very large code size on 32-bit kernels, including a recurring issue where gcc uses a large amount of stack. There's just not much benefit to this unrolling when the code is already so large. Let's roll up the rounds when !CONFIG_64BIT. To avoid having to duplicate the code, just write the code once using a loop, and conditionally use 'unrolled_full' from . Then, fold the now-unneeded ROUND() macro into the loop. Finally, also remove the now-unneeded override of the stack frame size warning. Code size improvements for blake2b_compress_generic(): Size before (bytes) Size after (bytes) ------------------- ------------------ i386, gcc 27584 3632 i386, clang 18208 3248 arm32, gcc 19912 2860 arm32, clang 21336 3344 Running the BLAKE2b benchmark on a !CONFIG_64BIT kernel on an x86_64 processor shows a 16384B throughput change of 351 => 340 MB/s (gcc) or 442 MB/s => 375 MB/s (clang). So clearly not much of a slowdown either. But also that microbenchmark also effectively disregards cache usage, which is important in practice and is far better in the smaller code. Note: If we rolled up the loop on x86_64 too, the change would be 7024 bytes => 1584 bytes and 1960 MB/s => 1396 MB/s (gcc), or 6848 bytes => 1696 bytes and 1920 MB/s => 1263 MB/s (clang). Maybe still worth it, though not quite as clearly beneficial. Fixes: 91d689337fe8 ("crypto: blake2b - add blake2b generic implementation") Reviewed-by: Ard Biesheuvel Link: https://lore.kernel.org/r/20251205050330.89704-1-ebiggers@kernel.org Signed-off-by: Eric Biggers --- lib/crypto/Makefile | 1 - lib/crypto/blake2b.c | 44 ++++++++++++++++++++------------------------ 2 files changed, 20 insertions(+), 25 deletions(-) diff --git a/lib/crypto/Makefile b/lib/crypto/Makefile index b5346cebbb55..330ab65b29c4 100644 --- a/lib/crypto/Makefile +++ b/lib/crypto/Makefile @@ -33,7 +33,6 @@ obj-$(CONFIG_CRYPTO_LIB_GF128MUL) += gf128mul.o obj-$(CONFIG_CRYPTO_LIB_BLAKE2B) += libblake2b.o libblake2b-y := blake2b.o -CFLAGS_blake2b.o := -Wframe-larger-than=4096 # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105930 ifeq ($(CONFIG_CRYPTO_LIB_BLAKE2B_ARCH),y) CFLAGS_blake2b.o += -I$(src)/$(SRCARCH) libblake2b-$(CONFIG_ARM) += arm/blake2b-neon-core.o diff --git a/lib/crypto/blake2b.c b/lib/crypto/blake2b.c index 09c6d65d8a6e..581b7f8486fa 100644 --- a/lib/crypto/blake2b.c +++ b/lib/crypto/blake2b.c @@ -14,6 +14,7 @@ #include #include #include +#include #include static const u8 blake2b_sigma[12][16] = { @@ -73,31 +74,26 @@ blake2b_compress_generic(struct blake2b_ctx *ctx, b = ror64(b ^ c, 63); \ } while (0) -#define ROUND(r) do { \ - G(r, 0, v[0], v[ 4], v[ 8], v[12]); \ - G(r, 1, v[1], v[ 5], v[ 9], v[13]); \ - G(r, 2, v[2], v[ 6], v[10], v[14]); \ - G(r, 3, v[3], v[ 7], v[11], v[15]); \ - G(r, 4, v[0], v[ 5], v[10], v[15]); \ - G(r, 5, v[1], v[ 6], v[11], v[12]); \ - G(r, 6, v[2], v[ 7], v[ 8], v[13]); \ - G(r, 7, v[3], v[ 4], v[ 9], v[14]); \ -} while (0) - ROUND(0); - ROUND(1); - ROUND(2); - ROUND(3); - ROUND(4); - ROUND(5); - ROUND(6); - ROUND(7); - ROUND(8); - ROUND(9); - ROUND(10); - ROUND(11); - +#ifdef CONFIG_64BIT + /* + * Unroll the rounds loop to enable constant-folding of the + * blake2b_sigma values. Seems worthwhile on 64-bit kernels. + * Not worthwhile on 32-bit kernels because the code size is + * already so large there due to BLAKE2b using 64-bit words. + */ + unrolled_full +#endif + for (int r = 0; r < 12; r++) { + G(r, 0, v[0], v[4], v[8], v[12]); + G(r, 1, v[1], v[5], v[9], v[13]); + G(r, 2, v[2], v[6], v[10], v[14]); + G(r, 3, v[3], v[7], v[11], v[15]); + G(r, 4, v[0], v[5], v[10], v[15]); + G(r, 5, v[1], v[6], v[11], v[12]); + G(r, 6, v[2], v[7], v[8], v[13]); + G(r, 7, v[3], v[4], v[9], v[14]); + } #undef G -#undef ROUND for (i = 0; i < 8; ++i) ctx->h[i] ^= v[i] ^ v[i + 8]; -- 2.47.3