diff mbox series

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

Message ID 20250609-curve25519-hacl64-disable-kasan-clang-v1-1-08ea0ac5ccff@kernel.org
State New
Headers show
Series crypto: lib/curve25519-hacl64 - Disable KASAN with clang-17 and older | expand

Commit Message

Nathan Chancellor June 9, 2025, 10:45 p.m. UTC 
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@kernel.org>
---
 lib/crypto/Makefile | 4 ++++
 1 file changed, 4 insertions(+)


---
base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
change-id: 20250609-curve25519-hacl64-disable-kasan-clang-faf6e97315e4

Best regards,
diff mbox series

Patch

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