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arm64: align randomized TEXT_OFFSET on 4 kB boundary 

When booting via UEFI, the kernel Image is loaded at a 4 kB boundary and
the embedded EFI stub is executed in place. The EFI stub relocates the
Image to reside TEXT_OFFSET bytes above a 2 MB boundary, and jumps into
the kernel proper.

In AArch64, PC relative symbol references are emitted using adrp/add or
adrp/ldr pairs, where the offset into a 4 kB page is resolved using a
separate :lo12: relocation. This implicitly assumes that the code will
always be executed at the same relative offset with respect to a 4 kB
boundary, or the references will point to the wrong address.

This means we should link the kernel at a 4 kB aligned base address in
order to remain compatible with the base address the UEFI loader uses
when doing the initial load of Image. So update the code that generates
TEXT_OFFSET to choose a multiple of 4 kB.

At the same time, update the code so it chooses from the interval [0..2MB)
as the author originally intended.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Ard Biesheuvel 2014-08-13 18:53:03 +01:00 committed by Will Deacon
parent 503e6636b6
commit 4190312beb
2 changed files with 5 additions and 5 deletions
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2
arch/arm64/Makefile
View File

@ -39,7 +39,7 @@ 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%04x0\n", int(65535 * rand())}')
TEXT_OFFSET := $(shell awk 'BEGIN {srand(); printf "0x%03x000\n", int(512 * rand())}')
else
TEXT_OFFSET := 0x00080000
endif

8
arch/arm64/kernel/head.S
View File

@ -38,11 +38,11 @@
#define KERNEL_RAM_VADDR (PAGE_OFFSET + TEXT_OFFSET)
#if (TEXT_OFFSET & 0xf) != 0
#error TEXT_OFFSET must be at least 16B aligned
#elif (PAGE_OFFSET & 0xfffff) != 0
#if (TEXT_OFFSET & 0xfff) != 0
#error TEXT_OFFSET must be at least 4KB aligned
#elif (PAGE_OFFSET & 0x1fffff) != 0
#error PAGE_OFFSET must be at least 2MB aligned
#elif TEXT_OFFSET > 0xfffff
#elif TEXT_OFFSET > 0x1fffff
#error TEXT_OFFSET must be less than 2MB
#endif