linux-kernel - Re: [PATCH] KEYS: trusted: fix -Wvarags warning

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Message-Id: <1539357951.2656.9.camel@linux.ibm.com>
Date:   Fri, 12 Oct 2018 08:25:51 -0700
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Denis Kenzior <denkenz@...il.com>, ndesaulniers@...gle.com,
        dhowells@...hat.com
Cc:     natechancellor@...il.com, ebiggers@...gle.com,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KEYS: trusted: fix -Wvarags warning

On Fri, 2018-10-12 at 10:13 -0500, Denis Kenzior wrote:
> Hi James,
> 
> > > So can't we simply use 'bool' or uint32 as the type for h3
> > > instead
> > > of re-ordering everything
> > 
> > The problem is the standard is ambiguious.  The only thing that's
> > guaranteed to work for all time is a char *.  If you want to keep
> > the
> > order, what I'd suggest is inserting a dummy pointer argument which
> > is
> > always expected to be NULL between the h3 and the varargs.
> https://patchwork.kernel.org/patch/10274411/
> So maybe I'm misunderstanding something, but the issue seems to be
> that 
> unsigned char is promoted to 'unsigned char *' by Clang and probably 
> unsigned int or int by gcc.
> 
> So instead of having unsigned char h3, can't we simply have bool h3
> or unsigned int h3?

Or actually, we fix this like I did for tpm2 in an unmerged patch and
compute the hmac over the constructed buffer not using varargs:

https://patchwork.kernel.org/patch/10274411/

James