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Date:   Wed, 6 Jan 2021 13:23:24 -0700
From:   Nathan Chancellor <natechancellor@gmail.com>
To:     Alexander Lobakin <alobakin@pm.me>
Cc:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Kees Cook <keescook@chromium.org>,
        Fangrui Song <maskray@google.com>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        Alex Smith <alex.smith@imgtec.com>,
        Ralf Baechle <ralf@linux-mips.org>,
        Markos Chandras <markos.chandras@imgtec.com>,
        linux-mips@vger.kernel.org, stable@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 mips-next 3/4] MIPS: vmlinux.lds.S: catch bad .got,
 .plt and .rel.dyn at link time
Message-ID: <20210106202324.GA2953310@ubuntu-m3-large-x86>
References: <20210106200713.31840-1-alobakin@pm.me>
 <20210106200801.31993-1-alobakin@pm.me>
 <20210106200801.31993-3-alobakin@pm.me>
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In-Reply-To: <20210106200801.31993-3-alobakin@pm.me>
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On Wed, Jan 06, 2021 at 08:08:29PM +0000, Alexander Lobakin wrote:
> Catch any symbols placed in .got, .got.plt, .plt, .rel.dyn
> or .rela.dyn and check for these sections to be zero-sized
> at link time.
> 
> At least two of them were noticed in real builds:
> 
> mips-alpine-linux-musl-ld: warning: orphan section `.rel.dyn'
> from `init/main.o' being placed in section `.rel.dyn'
> 
> ld.lld: warning: <internal>:(.got) is being placed in '.got'
> 
> Adopted from x86/kernel/vmlinux.lds.S.
> 
> Reported-by: Nathan Chancellor <natechancellor@gmail.com> # .got
> Suggested-by: Fangrui Song <maskray@google.com> # .rel.dyn
> Signed-off-by: Alexander Lobakin <alobakin@pm.me>
> ---
>  arch/mips/kernel/vmlinux.lds.S | 35 ++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
> 
> diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
> index 5d6563970ab2..05eda9d9a7d5 100644
> --- a/arch/mips/kernel/vmlinux.lds.S
> +++ b/arch/mips/kernel/vmlinux.lds.S
> @@ -227,4 +227,39 @@ SECTIONS
>  		*(.pdr)
>  		*(.reginfo)
>  	}
> +
> +	/*
> +	 * Sections that should stay zero sized, which is safer to
> +	 * explicitly check instead of blindly discarding.
> +	 */
> +
> +	.got : {
> +		*(.got)
> +		*(.igot.*)
> +	}
> +	ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")

This assertion does trigger now.

$ make -skj"$(nproc)" ARCH=mips CROSS_COMPILE=mipsel-linux-gnu- LLVM=1 \
       O=out/mipsel distclean malta_kvm_guest_defconfig all
...
ld.lld: error: Unexpected GOT entries detected!
ld.lld: error: Unexpected GOT entries detected!
...

> +	.got.plt (INFO) : {
> +		*(.got.plt)
> +	}
> +	ASSERT(SIZEOF(.got.plt) == 0, "Unexpected GOT/PLT entries detected!")
> +
> +	.plt : {
> +		*(.plt)
> +		*(.plt.*)
> +		*(.iplt)
> +	}
> +	ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
> +
> +	.rel.dyn : {
> +		*(.rel.*)
> +		*(.rel_*)
> +	}
> +	ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!")
> +
> +	.rela.dyn : {
> +		*(.rela.*)
> +		*(.rela_*)
> +	}
> +	ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")
>  }
> -- 
> 2.30.0
> 
>