linux-kernel - Re: [PATCH v2 mips-next 3/4] MIPS: vmlinux.lds.S: catch bad .got, .plt and .rel.dyn at link time

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Date:   Wed, 06 Jan 2021 20:28:46 +0000
From:   Alexander Lobakin <alobakin@...me>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Alexander Lobakin <alobakin@...me>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Kees Cook <keescook@...omium.org>,
        Fangrui Song <maskray@...gle.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Alex Smith <alex.smith@...tec.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Markos Chandras <markos.chandras@...tec.com>,
        linux-mips@...r.kernel.org, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 mips-next 3/4] MIPS: vmlinux.lds.S: catch bad .got, .plt and .rel.dyn at link time

From: Nathan Chancellor <natechancellor@...il.com>
Date: Wed, 6 Jan 2021 13:23:24 -0700

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@...il.com> # .got
>> Suggested-by: Fangrui Song <maskray@...gle.com> # .rel.dyn
>> Signed-off-by: Alexander Lobakin <alobakin@...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!
> ...

Oops. I'll build my kernel with LLVM stack and dig into it deeper
tomorrow.

>> +	.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

Thanks,
Al