From 2f13daee2a72bb962f5fd356c3a263a6f16da965 Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Mon, 9 Jun 2025 15:45:20 -0700 Subject: [PATCH] lib/crypto/curve25519-hacl64: Disable KASAN with clang-17 and older After commit 6f110a5e4f99 ("Disable SLUB_TINY for build testing"), which causes CONFIG_KASAN to be enabled in allmodconfig again, arm64 allmodconfig builds with clang-17 and older show an instance of -Wframe-larger-than (which breaks the build with CONFIG_WERROR=y): lib/crypto/curve25519-hacl64.c:757:6: error: stack frame size (2336) exceeds limit (2048) in 'curve25519_generic' [-Werror,-Wframe-larger-than] 757 | void curve25519_generic(u8 mypublic[CURVE25519_KEY_SIZE], | ^ When KASAN is disabled, the stack usage is roughly quartered: lib/crypto/curve25519-hacl64.c:757:6: error: stack frame size (608) exceeds limit (128) in 'curve25519_generic' [-Werror,-Wframe-larger-than] 757 | void curve25519_generic(u8 mypublic[CURVE25519_KEY_SIZE], | ^ Using '-Rpass-analysis=stack-frame-layout' shows the following variables and many, many 8-byte spills when KASAN is enabled: Offset: [SP-144], Type: Variable, Align: 8, Size: 40 Offset: [SP-464], Type: Variable, Align: 8, Size: 320 Offset: [SP-784], Type: Variable, Align: 8, Size: 320 Offset: [SP-864], Type: Variable, Align: 32, Size: 80 Offset: [SP-896], Type: Variable, Align: 32, Size: 32 Offset: [SP-1016], Type: Variable, Align: 8, Size: 120 When KASAN is disabled, there are still spills but not at many and the variables list is smaller: Offset: [SP-192], Type: Variable, Align: 32, Size: 80 Offset: [SP-224], Type: Variable, Align: 32, Size: 32 Offset: [SP-344], Type: Variable, Align: 8, Size: 120 Disable KASAN for this file when using clang-17 or older to avoid blowing out the stack, clearing up the warning. Signed-off-by: Nathan Chancellor Acked-by: "Jason A. Donenfeld" Acked-by: Ard Biesheuvel Link: https://lore.kernel.org/r/20250609-curve25519-hacl64-disable-kasan-clang-v1-1-08ea0ac5ccff@kernel.org Signed-off-by: Eric Biggers --- lib/crypto/Makefile | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/lib/crypto/Makefile b/lib/crypto/Makefile index 3e79283b617d..18664127ecd6 100644 --- a/lib/crypto/Makefile +++ b/lib/crypto/Makefile @@ -35,6 +35,10 @@ obj-$(CONFIG_CRYPTO_LIB_CURVE25519_GENERIC) += libcurve25519-generic.o libcurve25519-generic-y := curve25519-fiat32.o libcurve25519-generic-$(CONFIG_ARCH_SUPPORTS_INT128) := curve25519-hacl64.o libcurve25519-generic-y += curve25519-generic.o +# clang versions prior to 18 may blow out the stack with KASAN +ifeq ($(call clang-min-version, 180000),) +KASAN_SANITIZE_curve25519-hacl64.o := n +endif obj-$(CONFIG_CRYPTO_LIB_CURVE25519) += libcurve25519.o libcurve25519-y += curve25519.o -- 2.50.1