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

[Ard Biesheuvel]

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>
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