linux-kernel - Re: [PATCH] lib/crypto: curve25519-hacl64: Fix older clang KASAN workaround for GCC

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Message-ID: <20251103184846.GA672460@ax162>
Date: Mon, 3 Nov 2025 11:48:46 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Eric Biggers <ebiggers@...nel.org>
Cc: "Jason A. Donenfeld" <Jason@...c4.com>,
	Ard Biesheuvel <ardb@...nel.org>, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] lib/crypto: curve25519-hacl64: Fix older clang KASAN
 workaround for GCC

On Mon, Nov 03, 2025 at 09:00:36AM -0800, Eric Biggers wrote:
> On Sun, Nov 02, 2025 at 09:35:03PM -0500, Nathan Chancellor wrote:
> > Commit 2f13daee2a72 ("lib/crypto/curve25519-hacl64: Disable KASAN with
> > clang-17 and older") inadvertently disabled KASAN in curve25519-hacl64.o
> > for GCC unconditionally because clang-min-version will always evaluate
> > to nothing for GCC. Add a check for CONFIG_CC_IS_GCC to avoid the
> > workaround, which is only needed for clang-17 and older.
> > 
> > Additionally, invert the 'ifeq (...,)' into 'ifneq (...,y)', as it is a
> > little easier to read and understand the intention ("if not GCC or at
> > least clang-18, disable KASAN").
> > 
> > Cc: stable@...r.kernel.org
> > Fixes: 2f13daee2a72 ("lib/crypto/curve25519-hacl64: Disable KASAN with clang-17 and older")
> > Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> > ---
> >  lib/crypto/Makefile | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/lib/crypto/Makefile b/lib/crypto/Makefile
> > index bded351aeace..372b7a12b371 100644
> > --- a/lib/crypto/Makefile
> > +++ b/lib/crypto/Makefile
> > @@ -90,7 +90,7 @@ else
> >  libcurve25519-$(CONFIG_CRYPTO_LIB_CURVE25519_GENERIC) += curve25519-fiat32.o
> >  endif
> >  # clang versions prior to 18 may blow out the stack with KASAN
> > -ifeq ($(call clang-min-version, 180000),)
> > +ifneq ($(CONFIG_CC_IS_GCC)$(call clang-min-version, 180000),y)
> >  KASAN_SANITIZE_curve25519-hacl64.o := n
> >  endif
> 
> Thanks for catching this!
> 
> Using CONFIG_CC_IS_GCC == "" to check for clang seems a bit odd when
> there's already a CONFIG_CC_IS_CLANG available.
> 
> How about we do it like this?
> 
>     ifeq ($(CONFIG_CC_IS_CLANG)_$(call clang-min-version, 180000),y_)

Yeah, I am not really sure why I was being so cryptic with the original
way it was written :) I think it made a little more sense when it was
'ifeq'. Technically we could do without the _ but would you prefer that
I keep it? I can send a v2 with whatever you prefer and an updated
commit message.

Cheers,
Nathan