linux-kernel - Re: [PATCH v4 14/17] arm/build: Warn on orphan section placement

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Message-ID: <20200629181514.GA1046442@rani.riverdale.lan>
Date:   Mon, 29 Jun 2020 14:15:14 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Kees Cook <keescook@...omium.org>,
        Will Deacon <will@...nel.org>,
        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>,
        Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        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 v4 14/17] arm/build: Warn on orphan section placement

On Mon, Jun 29, 2020 at 07:07:04PM +0100, Russell King - ARM Linux admin wrote:
> On Mon, Jun 29, 2020 at 11:54:01AM -0400, Arvind Sankar wrote:
> > On Sun, Jun 28, 2020 at 11:18:37PM -0700, Kees Cook wrote:
> > > We don't want to depend on the linker's orphan section placement
> > > heuristics as these can vary between linkers, and may change between
> > > versions. All sections need to be explicitly named in the linker
> > > script.
> > > 
> > > Specifically, this would have made a recently fixed bug very obvious:
> > > 
> > > ld: warning: orphan section `.fixup' from `arch/arm/lib/copy_from_user.o' being placed in section `.fixup'
> > > 
> > > Discard unneeded sections .iplt, .rel.iplt, .igot.plt, and .modinfo.
> > > 
> > > Add missing text stub sections .vfp11_veneer and .v4_bx.
> > > 
> > > Add debug sections explicitly.
> > > 
> > > Finally enable orphan section warning.
> > 
> > This is unrelated to this patch as such, but I noticed that ARM32/64 places
> > the .got section inside .text -- is that expected on ARM?
> 
> Do you mean in general, in the kernel vmlinux, in the decompressor
> vmlinux or ... ?
> 

Sorry, in the kernel vmlinux. ARM_TEXT includes *(.got) for 32-bit, and
the 64-bit vmlinux.lds.S includes it in .text as well. The decompressor
for 32-bit keeps it separate for non-EFI stub kernel and puts it inside
.data for EFI stub.