diff options
authorArd Biesheuvel <ard.biesheuvel@linaro.org>2014-08-13 18:53:03 +0100
committerMark Brown <broonie@kernel.org>2015-01-22 21:27:27 +0000
commitc86df325d594f33eff078fe6b6014f1994f9bcb7 (patch)
parent432d182423d53bc7f03d3a399cd57482c5ca47b0 (diff)
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> (cherry picked from commit 4190312beb2acfb7bfb1bb971e24a759aa96b0e8) Signed-off-by: Mark Brown <broonie@kernel.org> Conflicts: arch/arm64/Makefile arch/arm64/kernel/head.S
2 files changed, 10 insertions, 2 deletions
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 7ab6b358cc35..a5004a5b7aa4 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -32,7 +32,11 @@ CHECKFLAGS += -D__aarch64__
head-y := arch/arm64/kernel/head.o
# The byte offset of the kernel image in RAM from the start of RAM.
+TEXT_OFFSET := $(shell awk 'BEGIN {srand(); printf "0x%03x000\n", int(512 * rand())}')
TEXT_OFFSET := 0x00080000
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 7218fefc6ac9..9129a917203e 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -37,8 +37,12 @@
-#if (KERNEL_RAM_VADDR & 0xfffff) != 0x80000
-#error KERNEL_RAM_VADDR must start at 0xXXX80000
+#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 > 0x1fffff
+#error TEXT_OFFSET must be less than 2MB
.macro pgtbl, ttb0, ttb1, virt_to_phys