linux-kernel - Re: [PATCH v2 05/39] x86: Base IBT bits

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Date:   Fri, 25 Feb 2022 14:41:52 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        jpoimboe@...hat.com, andrew.cooper3@...rix.com,
        linux-kernel@...r.kernel.org, ndesaulniers@...gle.com,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com, mbenes@...e.cz, rostedt@...dmis.org,
        mhiramat@...nel.org, alexei.starovoitov@...il.com,
        Nathan Chancellor <nathan@...nel.org>, llvm@...ts.linux.dev
Subject: Re: [PATCH v2 05/39] x86: Base IBT bits

On Thu, Feb 24, 2022 at 04:35:51PM -0800, Kees Cook wrote:

> > --- a/arch/x86/Makefile
> > +++ b/arch/x86/Makefile
> > @@ -36,7 +36,7 @@ endif
> >  
> >  # How to compile the 16-bit code.  Note we always compile for -march=i386;
> >  # that way we can complain to the user if the CPU is insufficient.
> > -REALMODE_CFLAGS	:= -m16 -g -Os -DDISABLE_BRANCH_PROFILING \
> > +REALMODE_CFLAGS	:= -m16 -g -Os -DDISABLE_BRANCH_PROFILING -D__DISABLE_EXPORTS \
> >  		   -Wall -Wstrict-prototypes -march=i386 -mregparm=3 \
> >  		   -fno-strict-aliasing -fomit-frame-pointer -fno-pic \
> >  		   -mno-mmx -mno-sse $(call cc-option,-fcf-protection=none)
> 
> This change seems important separately from this patch, yes? (Or at
> least a specific call-out in the commit log.)

It was to not stuff endbr in realmode code. *something* complained about
it (and Joao independently mentioned it on IRC).

Could be I hit some compile fail somewhere and this was the cleanest way
to simply make it go away.

I'll go mention it somewhere.