From 4190312beb2acfb7bfb1bb971e24a759aa96b0e8 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Wed, 13 Aug 2014 18:53:03 +0100 Subject: [PATCH] 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 Signed-off-by: Ard Biesheuvel Signed-off-by: Will Deacon --- arch/arm64/Makefile | 2 +- arch/arm64/kernel/head.S | 8 ++++---- 2 files changed, 5 insertions(+), 5 deletions(-) diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index 5783354..2df5e5d 100644 --- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -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 diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 144f105..bed0283 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -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 -- 2.7.4