linux-kernel - Re: [PATCH v3 0/7] crypto: x86: Fix indirect function call casts

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Date:   Tue, 7 May 2019 14:50:46 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Joao Moreira <jmoreira@...e.de>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, X86 ML <x86@...nel.org>,
        linux-crypto <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v3 0/7] crypto: x86: Fix indirect function call casts

On Tue, May 07, 2019 at 02:07:51PM -0700, Kees Cook wrote:
> On Tue, May 7, 2019 at 10:00 AM Eric Biggers <ebiggers@...nel.org> wrote:
> > > Given the above, the current efforts to improve the Linux security,
> > > and the upcoming kernel support to compilers with CFI features, this
> > > creates macros to be used to build the needed function definitions,
> > > to be used in camellia, cast6, serpent, twofish, and aesni.
> >
> > So why not change the function prototypes to be compatible with common_glue_*_t
> > instead, rather than wrapping them with another layer of functions?  Is it
> > because indirect calls into asm code won't be allowed with CFI?
> 
> I don't know why they're not that way to begin with. But given that
> the casting was already happening, this is just moving it to a place
> where CFI won't be angry. :)
> 
> > >   crypto: x86/crypto: Use new glue function macros
> >
> > This one should be "x86/serpent", not "x86/crypto".
> 
> Oops, yes, that's my typo. I'll fix for v4. Do the conversions
> themselves look okay (the changes are pretty mechanical)? If so,
> Herbert, do you want a v4 with the typo fix, or do you want to fix
> that up yourself?
> 
> Thanks!
> 

I don't know yet.  It's difficult to read the code with 2 layers of macros.

Hence why I asked why you didn't just change the prototypes to be compatible.

- Eric