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

[linux@armlinux.org.uk (Russell King - ARM Linux)]

On Wed, Oct 04, 2017 at 01:20:26PM +0100, Ard Biesheuvel wrote:
> On 4 October 2017 at 13:16, Gregory CLEMENT
> <gregory.clement@free-electrons.com> wrote:
> > Hi Ard,
> >
> >  On ven., sept. 08 2017, Ard Biesheuvel <ard.biesheuvel@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@armlinux.org.uk>
> >> Fixes: e4bae4d0b5f3 ("arm/efi: Split zImage code and data into separate ...")
> >> Tested-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> >
> > Any new for this patch?
> >
> > It is not yet in v4.14-rc whereas "arm/efi: Split zImage code and data
> > into separate ..." was already merged. So currently I have many boards
> > which still does not boot in v4.14-rc3.
> >
> 
> Russell, any objections?

It would be nice if there was something in the commit log that described
why we need to align data that is basically a byte stream, and which
decompressor methods it affects.  Maybe the decompressors should cope
with a misaligned byte stream - what if (for example) someone supplies
the kernel with a compressed initramfs image that is not word aligned?
We already have people using non-page aligned compressed initramfs
images.

-- 
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