linux/arch/arm64/Kconfig.debug
Mark Rutland da57a369d3 arm64: Enable TEXT_OFFSET fuzzing
The arm64 Image header contains a text_offset field which bootloaders
are supposed to read to determine the offset (from a 2MB aligned "start
of memory" per booting.txt) at which to load the kernel. The offset is
not well respected by bootloaders at present, and due to the lack of
variation there is little incentive to support it. This is unfortunate
for the sake of future kernels where we may wish to vary the text offset
(even zeroing it).

This patch adds options to arm64 to enable fuzz-testing of text_offset.
CONFIG_ARM64_RANDOMIZE_TEXT_OFFSET forces the text offset to a random
16-byte aligned value value in the range [0..2MB) upon a build of the
kernel. It is recommended that distribution kernels enable randomization
to test bootloaders such that any compliance issues can be fixed early.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Tom Rini <trini@ti.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2014-07-10 12:36:58 +01:00

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menu "Kernel hacking"
source "lib/Kconfig.debug"
config FRAME_POINTER
bool
default y
config STRICT_DEVMEM
bool "Filter access to /dev/mem"
depends on MMU
help
If this option is disabled, you allow userspace (root) access to all
of memory, including kernel and userspace memory. Accidental
access to this is obviously disastrous, but specific access can
be used by people debugging the kernel.
If this option is switched on, the /dev/mem file only allows
userspace access to memory mapped peripherals.
If in doubt, say Y.
config PID_IN_CONTEXTIDR
bool "Write the current PID to the CONTEXTIDR register"
help
Enabling this option causes the kernel to write the current PID to
the CONTEXTIDR register, at the expense of some additional
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.
endmenu