[PATCH] ARM: compressed: discard ksym/kcrctab input section

[Gregory CLEMENT]

Hi Ard,
 
 On ven., sept. 08 2017, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:

> As it turns out, building the ARM kernel with EFI support pulls in
> a couple of sections that we don't really need in the decompressor.
> This is due to the fact the the UEFI stub uses sort() to sort the UEFI
> memory map, which is an exported symbol pulled in from lib/sort.c.
>
> Before commit e4bae4d0b5f3 ("arm/efi: Split zImage code and data into
> separate PE/COFF sections"), this resulted in the following layout
> for the decompressor ELF binary.
>
>   [Nr] Name              Type     Addr     Off    Size   ES Flg Lk Inf Al
>   [ 0]                   NULL     00000000 000000 000000 00      0   0  0
>   [ 1] .text             PROGBITS 00000000 010000 009b3c 00  AX  0   0 512
>   [ 2] .rodata           PROGBITS 00009b3c 019b3c 001684 00   A  0   0  4
>   [ 3] __ksymtab_strings PROGBITS 0000b1c0 01b1c0 000005 00   A  0   0  1
>   [ 4] .data             PROGBITS 0000b1c8 01b1c8 000020 00  WA  0   0  8
>   [ 5] ___ksymtab+sort   PROGBITS 0000b1e8 01b1e8 000008 00  WA  0   0  4
>   [ 6] .piggydata        PROGBITS 0000b1f0 01b1f0 77ac38 00   A  0   0  1
>   [ 7] .got.plt          PROGBITS 00785e28 795e28 00000c 04  WA  0   0  4
>   [ 8] .got              PROGBITS 00785e34 795e34 000028 00  WA  0   0  4
>   [ 9] .pad              PROGBITS 00785e5c 795e5c 000004 00  WA  0   0  1
>   [10] .bss              NOBITS   00785e60 795e60 00001c 00  WA  0   0  4
>   [11] .stack            NOBITS   00785e80 795e60 001000 00  WA  0   0  1
>
> Commit e4bae4d0b5f3 made some changes to the linker script to allow the
> UEFI firmware to map the decompressor with strict R-X/RW- permissions
> before invoking it. Unfortunately, this turns out to break the boot on
> some systems, because the linker now also moves the ksymtab/kcrctab
> sections around, resulting in .piggydata to appear misaligned.
>
>   [Nr] Name              Type     Addr     Off    Size   ES Flg Lk Inf Al
>   [ 0]                   NULL     00000000 000000 000000 00      0   0  0
>   [ 1] .text             PROGBITS 00000000 010000 00a93c 00  AX  0   0 4096
>   [ 2] .rodata           PROGBITS 0000a93c 01a93c 001684 00   A  0   0  4
>   [ 3] __ksymtab_strings PROGBITS 0000bfc0 01bfc0 000005 00   A  0   0  1
>   [ 4] .piggydata        PROGBITS 0000bfc5 01bfc5 77ac47 00   A  0   0  1
>   [ 5] .got.plt          PROGBITS 00786c0c 796c0c 00000c 04  WA  0   0  4
>   [ 6] .got              PROGBITS 00786c18 796c18 000028 00  WA  0   0  4
>   [ 7] .pad              PROGBITS 00786c40 796c40 000008 00  WA  0   0  1
>   [ 8] .data             PROGBITS 00787000 797000 000200 00  WA  0   0 4096
>   [ 9] ___ksymtab+sort   PROGBITS 00787200 797200 000008 00  WA  0   0  4
>   [10] .bss              NOBITS   00787208 797208 00001c 00  WA  0   0  4
>   [11] .stack            NOBITS   00787228 797208 001000 00  WA  0   0  1
>
> So let's align piggydata explicitly, and discard these sections from the
> binary.
>
> Cc: Russell King <linux at armlinux.org.uk>
> Fixes: e4bae4d0b5f3 ("arm/efi: Split zImage code and data into separate ...")
> Tested-by: Gregory CLEMENT <gregory.clement at free-electrons.com>

Actually I had not tested a kernel with these two changes in the same
time. But now I've just done it, and it still works, so the patch and my
tested-by remain valid.

Thanks!


> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> ---
>  arch/arm/boot/compressed/piggy.S       | 1 +
>  arch/arm/boot/compressed/vmlinux.lds.S | 1 +
>  2 files changed, 2 insertions(+)
>
> diff --git a/arch/arm/boot/compressed/piggy.S b/arch/arm/boot/compressed/piggy.S
> index f72088495f43..5d52c556dd32 100644
> --- a/arch/arm/boot/compressed/piggy.S
> +++ b/arch/arm/boot/compressed/piggy.S
> @@ -1,5 +1,6 @@
>  	.section .piggydata,#alloc
>  	.globl	input_data
> +	.align	2
>  input_data:
>  	.incbin	"arch/arm/boot/compressed/piggy_data"
>  	.globl	input_data_end
> diff --git a/arch/arm/boot/compressed/vmlinux.lds.S b/arch/arm/boot/compressed/vmlinux.lds.S
> index 7a4c59154361..5c5265be4605 100644
> --- a/arch/arm/boot/compressed/vmlinux.lds.S
> +++ b/arch/arm/boot/compressed/vmlinux.lds.S
> @@ -29,6 +29,7 @@ SECTIONS
>       * of the text/got segments.
>       */
>      *(.data)
> +    *(*ksymtab* *kcrctab*)
>    }
>  
>    . = TEXT_START;
> -- 
> 2.11.0
>

-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com