* [PATCH] arm64: remove TEXT_OFFSET randomization
@ 2020-06-15 10:19 Ard Biesheuvel
2020-06-15 10:27 ` Mark Rutland
2020-06-15 16:34 ` Will Deacon
0 siblings, 2 replies; 3+ messages in thread
From: Ard Biesheuvel @ 2020-06-15 10:19 UTC (permalink / raw)
To: linux-arm-kernel; +Cc: mark.rutland, will, Ard Biesheuvel
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
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^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] arm64: remove TEXT_OFFSET randomization
2020-06-15 10:19 [PATCH] arm64: remove TEXT_OFFSET randomization Ard Biesheuvel
@ 2020-06-15 10:27 ` Mark Rutland
2020-06-15 16:34 ` Will Deacon
1 sibling, 0 replies; 3+ messages in thread
From: Mark Rutland @ 2020-06-15 10:27 UTC (permalink / raw)
To: Ard Biesheuvel; +Cc: will, linux-arm-kernel
On Mon, Jun 15, 2020 at 12:19:39PM +0200, Ard Biesheuvel wrote:
> 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>
If nothing else, it's nice to see the scary awk go, so:
Acked-by: Mark Rutland <mark.rutland@arm.com>
Mark.
> ---
> 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
>
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^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] arm64: remove TEXT_OFFSET randomization
2020-06-15 10:19 [PATCH] arm64: remove TEXT_OFFSET randomization Ard Biesheuvel
2020-06-15 10:27 ` Mark Rutland
@ 2020-06-15 16:34 ` Will Deacon
1 sibling, 0 replies; 3+ messages in thread
From: Will Deacon @ 2020-06-15 16:34 UTC (permalink / raw)
To: Ard Biesheuvel, linux-arm-kernel
Cc: mark.rutland, catalin.marinas, Will Deacon
On Mon, 15 Jun 2020 12:19:39 +0200, Ard Biesheuvel wrote:
> 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.
>
> [...]
Applied to arm64 (for-next/fixes), thanks!
[1/1] arm64: remove TEXT_OFFSET randomization
https://git.kernel.org/arm64/c/751c263bb74f
Cheers,
--
Will
https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev
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2020-06-15 10:27 ` Mark Rutland
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