linux-hardening - Re: [PATCH] Compiler Attributes: counted_by: Adjust name and identifier expansion

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Date:   Thu, 17 Aug 2023 14:00:22 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] Compiler Attributes: counted_by: Adjust name and
 identifier expansion

On Thu, Aug 17, 2023 at 01:13:04PM -0700, Nathan Chancellor wrote:
> On Thu, Aug 17, 2023 at 01:06:03PM -0700, Kees Cook wrote:
> > GCC and Clang's current RFCs name this attribute "counted_by", and have
> > moved away from using a string for the member name. Update the kernel's
> > macros to match. Additionally provide a UAPI no-op macro for UAPI structs
> > that will gain annotations.
> > 
> > Cc: Miguel Ojeda <ojeda@...nel.org>
> > Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> > Fixes: dd06e72e68bc ("Compiler Attributes: Add __counted_by macro")
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> 
> Reviewed-by: Nathan Chancellor <nathan@...nel.org>
> 
> One comment below.
> 
> > ---
> >  include/linux/compiler_attributes.h | 26 +++++++++++++-------------
> >  include/uapi/linux/stddef.h         |  4 ++++
> >  2 files changed, 17 insertions(+), 13 deletions(-)
> > 
> > diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
> > index 00efa35c350f..74716a407aac 100644
> > --- a/include/linux/compiler_attributes.h
> > +++ b/include/linux/compiler_attributes.h
> > @@ -94,6 +94,19 @@
> >  # define __copy(symbol)
> >  #endif
> >  
> > +/*
> > + * Optional: only supported since gcc >= 14
> > + * Optional: only supported since clang >= 17
> 
> Since you are in the area, should the supported clang version be
> optimistically updated to '18'? 17.x has already branched and I suspect
> it would be too late in the release cycle to cherry-pick that change
> from main if it were landed today (which seems pretty unlikely, given
> there do not appear to be many reviews from high profile clang folks
> yet).

Oops, yes. Excellent point. I'll bump this to 18.

-Kees

> 
> > + *
> > + *   gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
> > + * clang: https://reviews.llvm.org/D148381
> > + */
> > +#if __has_attribute(__counted_by__)
> > +# define __counted_by(member)		__attribute__((__counted_by__(member)))
> > +#else
> > +# define __counted_by(member)
> > +#endif
> > +
> >  /*
> >   * Optional: not supported by gcc
> >   * Optional: only supported since clang >= 14.0
> > @@ -129,19 +142,6 @@
> >  # define __designated_init
> >  #endif
> >  
> > -/*
> > - * Optional: only supported since gcc >= 14
> > - * Optional: only supported since clang >= 17
> > - *
> > - *   gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
> > - * clang: https://reviews.llvm.org/D148381
> > - */
> > -#if __has_attribute(__element_count__)
> > -# define __counted_by(member)		__attribute__((__element_count__(#member)))
> > -#else
> > -# define __counted_by(member)
> > -#endif
> > -
> >  /*
> >   * Optional: only supported since clang >= 14.0
> >   *
> > diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h
> > index 7837ba4fe728..7c3fc3980881 100644
> > --- a/include/uapi/linux/stddef.h
> > +++ b/include/uapi/linux/stddef.h
> > @@ -45,3 +45,7 @@
> >  		TYPE NAME[]; \
> >  	}
> >  #endif
> > +
> > +#ifndef __counted_by
> > +#define __counted_by(m)
> > +#endif
> > -- 
> > 2.34.1
> > 

-- 
Kees Cook