Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <CAKwvOd=ypa8xE-kaDa7XtzPsBH8=Xu_pZj2rnWaeawNs=3dDkw@mail.gmail.com>
 <20200811173655.1162093-1-nivedita@alum.mit.edu> <CAKwvOdnjLfQ0fWsrFYDJ2O+qFAfEFnTEEnW-aHrPha8G3_WTrg@mail.gmail.com>
 <20200811224436.GA1302731@rani.riverdale.lan> <CAKwvOdnvyVapAJBchivu8SxoQriKEu1bAimm8688EH=uq5YMqA@mail.gmail.com>
 <20200811234340.GA1318440@rani.riverdale.lan> <CAKwvOdn5gCjcAVHZ3jHU+q=mD5rmFAHpEyHyLf7ixtdaQ3Z-PQ@mail.gmail.com>
 <20200812004158.GA1447296@rani.riverdale.lan>
In-Reply-To: <20200812004158.GA1447296@rani.riverdale.lan>
From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Wed, 12 Aug 2020 10:39:41 -0700
Message-ID: <CAKwvOdnQu_6_NNtzFfxpjsxNzbj4JwENXntzMicOE6ZbUrBZqw@mail.gmail.com>
Subject: Re: [PATCH] x86/boot/compressed: Disable relocation relaxation for
 non-pie link
To:     Arvind Sankar <nivedita@alum.mit.edu>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Fangrui Song <maskray@google.com>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        e5ten.arch@gmail.com,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "# 3.4.x" <stable@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Aug 11, 2020 at 5:42 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
>
> On Tue, Aug 11, 2020 at 04:51:23PM -0700, Nick Desaulniers wrote:
> > On Tue, Aug 11, 2020 at 4:43 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > >
> > > On Tue, Aug 11, 2020 at 04:04:40PM -0700, Nick Desaulniers wrote:
> > > > On Tue, Aug 11, 2020 at 3:44 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > > > >
> > > > > On Tue, Aug 11, 2020 at 10:58:40AM -0700, Nick Desaulniers wrote:
> > > > > > > Cc: stable@vger.kernel.org # 4.19.x
> > > > > >
> > > > > > Thanks Arvind, good write up.  Just curious about this stable tag, how
> > > > > > come you picked 4.19?  I can see boot failures in our CI for x86+LLD
> > > > > > back to 4.9.  Can we amend that tag to use `# 4.9`? I'd be happy to
> > > > > > help submit backports should they fail to apply cleanly.
> > > > > > https://travis-ci.com/github/ClangBuiltLinux/continuous-integration/builds/179237488
> > > > > >
> > > > >
> > > > > 4.19 renamed LDFLAGS to KBUILD_LDFLAGS. For 4.4, 4.9 and 4.14 the patch
> > > > > needs to be modified, KBUILD_LDFLAGS -> LDFLAGS, so I figured we should
> > > > > submit backports separately. For 4.19 onwards, it should apply without
> > > > > changes I think.
> > > >
> > > > Cool, sounds good.  I'll keep an eye out for when stable goes to pick this up.
> > > >
> > > > tglx, Ingo, BP, can we pretty please get this in tip/urgent for
> > > > inclusion into 5.9?
> > > > --
> > > > Thanks,
> > > > ~Nick Desaulniers
> > >
> > > Another alternative is to just do this unconditionally instead of even
> > > checking for the -pie flag. None of the GOTPCRELs are in the
> > > decompressor, so they shouldn't be performance-sensitive at all.
> > >
> > > It still wouldn't apply cleanly to all the stable versions, but
> > > backporting would be even simpler.
> > >
> > > What do you think?
> > >
> > > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> > > index 3962f592633d..10c2ba59d192 100644
> > > --- a/arch/x86/boot/compressed/Makefile
> > > +++ b/arch/x86/boot/compressed/Makefile
> > > @@ -43,6 +43,7 @@ KBUILD_CFLAGS += -Wno-pointer-sign
> > >  KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
> > >  KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
> > >  KBUILD_CFLAGS += -D__DISABLE_EXPORTS
> > > +KBUILD_CFLAGS += $(call as-option,-Wa$(comma)-mrelax-relocations=no)
> >
> > We'd still want it for KBUILD_AFLAGS, too, just to be safe. Maybe a
>
> KBUILD_CFLAGS gets included into KBUILD_AFLAGS, so this already does
> that.

Ah, right, just below it in the diff.

>
> > one line comment to the effect of `# remove me once we can link as
> > -pie` would help us rip off this band-aid in the future?  It's more
> > obvious that the added hunk can be reverted once -pie linkage is
> > achieved with the current patch; either are fine by me.  Thanks!
> >
> > >
> > >  KBUILD_AFLAGS  := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> > >  GCOV_PROFILE := n
> >
> >
> >
> > --
> > Thanks,
> > ~Nick Desaulniers


-- 
Thanks,
~Nick Desaulniers