arm64: remove TEXT_OFFSET randomization

TEXT_OFFSET was recently changed to 0x0, in preparation for its removal
at a later stage, and a warning is emitted into the kernel log when the
bootloader appears to have failed to take the TEXT_OFFSET image header
value into account.

Ironically, this warning itself fails to take TEXT_OFFSET into account,
and compares the kernel image's alignment modulo 2M against a hardcoded
value of 0x0, and so the warning will trigger spuriously when TEXT_OFFSET
randomization is enabled.

Given the intent to get rid of TEXT_OFFSET entirely, let's fix this
oversight by just removing support for TEXT_OFFSET randomization.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20200615101939.634391-1-ardb@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/Kconfig.debug

@@ -8,21 +8,6 @@ config PID_IN_CONTEXTIDR
 	  instructions during context switch. Say Y here only if you are
 	  planning to use hardware trace tools with this kernel.
 
-config ARM64_RANDOMIZE_TEXT_OFFSET
-	bool "Randomize TEXT_OFFSET at build time"
-	help
-	  Say Y here if you want the image load offset (AKA TEXT_OFFSET)
-	  of the kernel to be randomized at build-time. When selected,
-	  this option will cause TEXT_OFFSET to be randomized upon any
-	  build of the kernel, and the offset will be reflected in the
-	  text_offset field of the resulting Image. This can be used to
-	  fuzz-test bootloaders which respect text_offset.
-
-	  This option is intended for bootloader and/or kernel testing
-	  only. Bootloaders must make no assumptions regarding the value
-	  of TEXT_OFFSET and platforms must not require a specific
-	  value.
-
 config DEBUG_EFI
 	depends on EFI && DEBUG_INFO
 	bool "UEFI debugging"

arch/arm64/Makefile

@@ -121,13 +121,7 @@ endif
 head-y		:= arch/arm64/kernel/head.o
 
 # The byte offset of the kernel image in RAM from the start of RAM.
-ifeq ($(CONFIG_ARM64_RANDOMIZE_TEXT_OFFSET), y)
-TEXT_OFFSET := $(shell awk "BEGIN {srand(); printf \"0x%06x\n\", \
-		 int(2 * 1024 * 1024 / (2 ^ $(CONFIG_ARM64_PAGE_SHIFT)) * \
-		 rand()) * (2 ^ $(CONFIG_ARM64_PAGE_SHIFT))}")
-else
 TEXT_OFFSET := 0x0
-endif
 
 ifeq ($(CONFIG_KASAN_SW_TAGS), y)
 KASAN_SHADOW_SCALE_SHIFT := 4