From c86df325d594f33eff078fe6b6014f1994f9bcb7 Mon Sep 17 00:00:00 2001
From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
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 <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
---
arch/arm64/Makefile | 4 ++++
arch/arm64/kernel/head.S | 8 ++++++--
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.
+ifeq ($(CONFIG_ARM64_RANDOMIZE_TEXT_OFFSET), y)
+TEXT_OFFSET := $(shell awk 'BEGIN {srand(); printf "0x%03x000\n", int(512 * rand())}')
+else
TEXT_OFFSET := 0x00080000
+endif
export TEXT_OFFSET GZFLAGS
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 @@
#define KERNEL_RAM_VADDR (PAGE_OFFSET + TEXT_OFFSET)
-#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
#endif
.macro pgtbl, ttb0, ttb1, virt_to_phys
--
2.34.1