Commit dd4bc607 authored Jun 11, 2020 by Ard Biesheuvel Committed by Will Deacon Jun 11, 2020

arm64: warn on incorrect placement of the kernel by the bootloader

Commit cfa7ede2 ("arm64: set TEXT_OFFSET to 0x0 in preparation for
removing it entirely") results in boot failures when booting kernels that
are built without KASLR support on broken bootloaders that ignore the
TEXT_OFFSET value passed via the header, and use the default of 0x80000
instead.

To work around this, turn CONFIG_RELOCATABLE on by default, even if KASLR
itself (CONFIG_RANDOMIZE_BASE) is turned off, and require CONFIG_EXPERT
to be enabled to deviate from this. Then, emit a warning into the kernel
log if we are not booting via the EFI stub (which is permitted to deviate
from the placement restrictions) and the kernel base address is not placed
according to the rules as laid out in Documentation/arm64/booting.rst.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20200611124330.252163-1-ardb@kernel.org

Signed-off-by: Will Deacon <will@kernel.org>

parent a194c33f

arch/arm64/Kconfig

+2 −1

Original line number	Diff line number	Diff line
		@@ -1746,8 +1746,9 @@ config ARM64_DEBUG_PRIORITY_MASKING
		endif

		config RELOCATABLE
		bool
		bool "Build a relocatable kernel image" if EXPERT
		select ARCH_HAS_RELR
		default y
		help
		This builds the kernel as a Position Independent Executable (PIE),
		which retains all relocation metadata required to relocate the

arch/arm64/kernel/setup.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -319,6 +319,10 @@ void __init setup_arch(char **cmdline_p)

		xen_early_init();
		efi_init();

		if (!efi_enabled(EFI_BOOT) && ((u64)_text % MIN_KIMG_ALIGN) != 0)
		pr_warn(FW_BUG "Kernel image misaligned at boot, please fix your bootloader!");

		arm64_memblock_init();

		paging_init();

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