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SubjectRe: [PATCH v2 2/2] arm/boot: Warn on orphan section placement
On Mon, Jun 22, 2020 at 1:49 PM Kees Cook <keescook@chromium.org> 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.
>
> Use common macros for debug sections, discards, and text stubs. Add
> discards for unwanted .note, and .rel sections. Finally, enable orphan
> section warning.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> arch/arm/boot/compressed/Makefile | 2 ++
> arch/arm/boot/compressed/vmlinux.lds.S | 17 +++++++----------
> 2 files changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> index 00602a6fba04..b8a97d81662d 100644
> --- a/arch/arm/boot/compressed/Makefile
> +++ b/arch/arm/boot/compressed/Makefile
> @@ -128,6 +128,8 @@ endif
> LDFLAGS_vmlinux += --no-undefined
> # Delete all temporary local symbols
> LDFLAGS_vmlinux += -X
> +# Report orphan sections
> +LDFLAGS_vmlinux += --orphan-handling=warn
> # Next argument is a linker script
> LDFLAGS_vmlinux += -T
>
> diff --git a/arch/arm/boot/compressed/vmlinux.lds.S b/arch/arm/boot/compressed/vmlinux.lds.S
> index 09ac33f52814..c2a8509f876f 100644
> --- a/arch/arm/boot/compressed/vmlinux.lds.S
> +++ b/arch/arm/boot/compressed/vmlinux.lds.S
> @@ -2,6 +2,7 @@
> /*
> * Copyright (C) 2000 Russell King
> */
> +#include <asm/vmlinux.lds.h>
>
> #ifdef CONFIG_CPU_ENDIAN_BE8
> #define ZIMAGE_MAGIC(x) ( (((x) >> 24) & 0x000000ff) | \
> @@ -17,8 +18,11 @@ ENTRY(_start)
> SECTIONS
> {
> /DISCARD/ : {
> + ARM_COMMON_DISCARD
> *(.ARM.exidx*)
> *(.ARM.extab*)
> + *(.note.*)
> + *(.rel.*)

.rel.* is the only case I'm curious about. Why do we want it in
vmlinux, but not the compressed image? Should `.rel.*` just be part
of ARM_COMMON_DISCARD from the previous patch?

> /*
> * Discard any r/w data - this produces a link error if we have any,
> * which is required for PIC decompression. Local data generates
> @@ -36,9 +40,7 @@ SECTIONS
> *(.start)
> *(.text)
> *(.text.*)
> - *(.gnu.warning)
> - *(.glue_7t)
> - *(.glue_7)
> + ARM_STUBS_TEXT
> }
> .table : ALIGN(4) {
> _table_start = .;
> @@ -128,12 +130,7 @@ SECTIONS
> PROVIDE(__pecoff_data_size = ALIGN(512) - ADDR(.data));
> PROVIDE(__pecoff_end = ALIGN(512));
>
> - .stab 0 : { *(.stab) }
> - .stabstr 0 : { *(.stabstr) }
> - .stab.excl 0 : { *(.stab.excl) }
> - .stab.exclstr 0 : { *(.stab.exclstr) }
> - .stab.index 0 : { *(.stab.index) }
> - .stab.indexstr 0 : { *(.stab.indexstr) }
> - .comment 0 : { *(.comment) }
> + STABS_DEBUG
> + DWARF_DEBUG
> }
> ASSERT(_edata_real == _edata, "error: zImage file size is incorrect");
> --
> 2.25.1
>


--
Thanks,
~Nick Desaulniers

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