[PATCH] crypto: curve25519-hacl64 - Disable fortify-source for clang-10

From: Arnd Bergmann <arnd@arndb.de>
To: Herbert Xu <herbert@gondor.apana.org.au>,
	"David S. Miller" <davem@davemloft.net>
Cc: Arnd Bergmann <arnd@arndb.de>,
	"Jason A . Donenfeld" <Jason@zx2c4.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org,
	clang-built-linux@googlegroups.com
Subject: [PATCH] crypto: curve25519-hacl64 - Disable fortify-source for clang-10
Date: Tue,  5 May 2020 15:59:34 +0200	[thread overview]
Message-ID: <20200505135947.216022-1-arnd@arndb.de> (raw)

clang-10 produces a warning about excessive stack usage, as well
as rather unoptimized object code when CONFIG_FORTIFY_SOURCE is
set:

lib/crypto/curve25519-hacl64.c:759:6: error: stack frame size of 2400 bytes in function 'curve25519_generic' [-Werror,-Wframe-larger-than=]

Jason Donenfeld managed to track this down to the usage of
CONFIG_FORTIFY_SOURCE, and I found a minimal test case that illustrates
this happening on clang-10 but not clang-9 or clang-11.

To work around this, turn off fortification in this file.

Link: https://bugs.llvm.org/show_bug.cgi?id=45802
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 lib/crypto/curve25519-hacl64.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lib/crypto/curve25519-hacl64.c b/lib/crypto/curve25519-hacl64.c
index c7de61829a66..87adeb4f9276 100644
--- a/lib/crypto/curve25519-hacl64.c
+++ b/lib/crypto/curve25519-hacl64.c
@@ -10,6 +10,10 @@
  * integer types.
  */
 
+#if (CONFIG_CLANG_VERSION >= 100000) && (CONFIG_CLANG_VERSION < 110000)
+#define __NO_FORTIFY /* https://bugs.llvm.org/show_bug.cgi?id=45802 */
+#endif
+
 #include <asm/unaligned.h>
 #include <crypto/curve25519.h>
 #include <linux/string.h>
-- 
2.26.0

