linux-kernel - Re: [PATCH v6 00/29] Warn on orphan section placement

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Message-ID: <202009010816.80F4692@keescook>
Date:   Tue, 1 Sep 2020 08:17:53 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Borislav Petkov <bp@...e.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        James Morse <james.morse@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Arnd Bergmann <arnd@...db.de>, x86@...nel.org,
        clang-built-linux@...glegroups.com, linux-arch@...r.kernel.org,
        linux-efi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 00/29] Warn on orphan section placement

On Tue, Sep 01, 2020 at 10:16:47AM +0200, Ingo Molnar wrote:
> 
> * Ingo Molnar <mingo@...nel.org> wrote:
> 
> > 
> > * Ingo Molnar <mingo@...nel.org> wrote:
> > 
> > > 
> > > * Kees Cook <keescook@...omium.org> wrote:
> > > 
> > > > On Fri, Aug 21, 2020 at 12:42:41PM -0700, Kees Cook wrote:
> > > > > Hi Ingo,
> > > > > 
> > > > > Based on my testing, this is ready to go. I've reviewed the feedback on
> > > > > v5 and made a few small changes, noted below.
> > > > 
> > > > If no one objects, I'll pop this into my tree for -next. I'd prefer it
> > > > go via -tip though! :)
> > > > 
> > > > Thanks!
> > > 
> > > I'll pick it up today, it all looks very good now!
> > 
> > One thing I found in testing is that it doesn't handler older LD 
> > versions well enough:
> > 
> >   ld: unrecognized option '--orphan-handling=warn'

Oh! Uhm, yikes. Thanks for noticing this.

> > Could we just detect the availability of this flag, and emit a warning 
> > if it doesn't exist but otherwise not abort the build?

Yeah, I'll respin those patches.

> > This is with:
> > 
> >   GNU ld version 2.25-17.fc23

(At best, this is from 2015 ... but yes, min binutils in 2.23.)

> 
> I've resolved this for now by not applying the 5 patches that add the 
> actual orphan section warnings:
> 
>   arm64/build: Warn on orphan section placement
>   arm/build: Warn on orphan section placement
>   arm/boot: Warn on orphan section placement
>   x86/build: Warn on orphan section placement
>   x86/boot/compressed: Warn on orphan section placement
> 
> The new asserts plus the actual fixes/enhancements are enough changes 
> to test for now in any case. :-)

Yup! I'll respin the enabling patches. Thanks again!

-- 
Kees Cook