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Date:   Tue, 12 Jan 2021 21:29:15 +0100
From:   Arnd Bergmann <>
To:     Nathan Chancellor <>,
        Nick Desaulniers <>,
        Kees Cook <>,
        Stephen Rothwell <>,
        Andrew Morton <>
Cc:     Arnd Bergmann <>, Marco Elver <>,
        George Popescu <>,,
Subject: [PATCH] [v2] ubsan: disable unsigned-overflow check for i386

From: Arnd Bergmann <>

Building ubsan kernels even for compile-testing introduced these
warnings in my randconfig environment:

crypto/blake2b_generic.c:98:13: error: stack frame size of 9636 bytes in function 'blake2b_compress' [-Werror,-Wframe-larger-than=]
static void blake2b_compress(struct blake2b_state *S,
crypto/sha512_generic.c:151:13: error: stack frame size of 1292 bytes in function 'sha512_generic_block_fn' [-Werror,-Wframe-larger-than=]
static void sha512_generic_block_fn(struct sha512_state *sst, u8 const *src,
lib/crypto/curve25519-fiat32.c:312:22: error: stack frame size of 2180 bytes in function 'fe_mul_impl' [-Werror,-Wframe-larger-than=]
static noinline void fe_mul_impl(u32 out[10], const u32 in1[10], const u32 in2[10])
lib/crypto/curve25519-fiat32.c:444:22: error: stack frame size of 1588 bytes in function 'fe_sqr_impl' [-Werror,-Wframe-larger-than=]
static noinline void fe_sqr_impl(u32 out[10], const u32 in1[10])

Further testing showed that this is caused by
-fsanitize=unsigned-integer-overflow, but is isolated to the 32-bit
x86 architecture.

The one in blake2b immediately overflows the 8KB stack area architectures,
so better ensure this never happens by disabling the option for 32-bit

Fixes: d0a3ac549f38 ("ubsan: enable for all*config builds")
Signed-off-by: Arnd Bergmann <>
v2: only turn it off for i386 as discussed
 lib/Kconfig.ubsan | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
index 8b635fd75fe4..3a0b1c930733 100644
--- a/lib/Kconfig.ubsan
+++ b/lib/Kconfig.ubsan
@@ -123,6 +123,7 @@ config UBSAN_SIGNED_OVERFLOW
 	bool "Perform checking for unsigned arithmetic overflow"
 	depends on $(cc-option,-fsanitize=unsigned-integer-overflow)
+	depends on !X86_32 # avoid excessive stack usage on x86-32/clang
 	  This option enables -fsanitize=unsigned-integer-overflow which checks
 	  for overflow of any arithmetic operations with unsigned integers. This

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