Commit dd4bc607 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Will Deacon

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: default avatarArd Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20200611124330.252163-1-ardb@kernel.orgSigned-off-by: default avatarWill Deacon <will@kernel.org>
parent a194c33f
......@@ -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
......
......@@ -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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