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

[Ard Biesheuvel]

On 8 September 2017 at 16:39, Gregory CLEMENT
<gregory.clement at free-electrons.com> wrote:
> 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!
>

Thanks for confirming. I was a bit sneaky, but the added .align can
never make a difference when the section is already aligned. I don't
understand why just the .align is not sufficient, but the patch is
simple enough so I think I am not going to investigate any further.

Thanks