[PATCH] arm64: remove TEXT_OFFSET randomization

Ard Biesheuvel
2020-06-15T10:19:52Z

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>
---
arch/arm64/Kconfig.debug | 15 ---------------
arch/arm64/Makefile | 6 ------
2 files changed, 21 deletions(-)

diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
index cdf7ec0b975e..265c4461031f 100644
--- a/arch/arm64/Kconfig.debug
+++ b/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"
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 76359cfb328a..a0d94d063fa8 100644
--- a/arch/arm64/Makefile
+++ b/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
--
2.27.0