netdev - Re: [PATCH 1/3] s390/ctcm: Fix return type of ctc{mp,}m

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Date:   Wed, 2 Nov 2022 13:01:26 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Heiko Carstens <hca@...ux.ibm.com>,
        Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Alexandra Winter <wintera@...ux.ibm.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH 1/3] s390/ctcm: Fix return type of ctc{mp,}m_tx()

On Wed, Nov 02, 2022 at 08:48:42PM +0100, Heiko Carstens wrote:
> On Wed, Nov 02, 2022 at 09:32:50AM -0700, Nathan Chancellor wrote:
> > should s390 select ARCH_SUPPORTS_CFI_CLANG in the future.
> 
> Yes, s390 should select that :)
> 
> But, is there any switch or option I need to set when compiling clang,
> so it knows about the kcfi sanitizer?
> 
> I get:
> clang-16: error: unsupported option '-fsanitize=kcfi' for target 's390x-ibm-linux'
> 
> > clang --version
> clang version 16.0.0 (https://github.com/llvm/llvm-project.git e02110e2ab4dd71b276e887483f0e6e286d243ed)

You'll need the "generic arch support": https://reviews.llvm.org/D135411
which is _almost_ landed. Testing would be welcome, for sure!

Sami, do you have any notes on what common things were needed to get
arm64 and x86_64 booting under kCFI? My only oh-so-helpful notes are
"keep CFI away from early boot code". :P

-- 
Kees Cook