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lib/crypto/curve25519-hacl64: Disable KASAN with clang-17 and older

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After commit 6f110a5e4f ("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@kernel.org>
Acked-by: "Jason A. Donenfeld" <Jason@zx2c4.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250609-curve25519-hacl64-disable-kasan-clang-v1-1-08ea0ac5ccff@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
This commit is contained in:
Nathan Chancellor
2025-06-09 15:45:20 -07:00
committed by Eric Biggers
parent e202196b8a
commit 2f13daee2a
1 changed files with 4 additions and 0 deletions
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4
lib/crypto/Makefile
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@@ -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