On Mon, Jun 09, 2025 at 03:45:20PM -0700, Nathan Chancellor wrote:
> 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 <nathan@xxxxxxxxxx>
> ---
> 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
Seems reasonable. We've had a hassle with this for a while.
Acked-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
