4 files changed, 30 insertions, 2 deletions

diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
index 1c1b75629842..4ee8e90b7a45 100644
--- a/arch/arm64/Kconfig.debug
+++ b/arch/arm64/Kconfig.debug
@@ -28,4 +28,19 @@ config PID_IN_CONTEXTIDR
           instructions during context switch. Say Y here only if you are
           planning to use hardware trace tools with this kernel.
 
+config ARM64_RANDOMIZE_TEXT_OFFSET
+        bool "Randomize TEXT_OFFSET at build time"
+        help
+          Say Y here if you want the image load offset (AKA TEXT_OFFSET)
+          of the kernel to be randomized at build-time. When selected,
+          this option will cause TEXT_OFFSET to be randomized upon any
+          build of the kernel, and the offset will be reflected in the
+          text_offset field of the resulting Image. This can be used to
+          fuzz-test bootloaders which respect text_offset.
+
+          This option is intended for bootloader and/or kernel testing
+          only. Bootloaders must make no assumptions regarding the value
+          of TEXT_OFFSET and platforms must not require a specific
+          value.
+
 endmenu
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 8185a913c5ed..e8d025c1459e 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -38,7 +38,11 @@ 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%04x0\n", int(65535 * 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 3ba0fc02c0de..69dafe9621fd 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 & 0xf) != 0
+#error TEXT_OFFSET must be at least 16B aligned
+#elif (PAGE_OFFSET & 0xfffff) != 0
+#error PAGE_OFFSET must be at least 2MB aligned
+#elif TEXT_OFFSET > 0xfffff
+#error TEXT_OFFSET must be less than 2MB
 #endif
 
         .macro  pgtbl, ttb0, ttb1, virt_to_phys
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index a814768ae148..97f0c0429dfa 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -125,3 +125,8 @@ SECTIONS
  */
 ASSERT(((__hyp_idmap_text_start + PAGE_SIZE) > __hyp_idmap_text_end),
        "HYP init code too big")
+
+/*
+ * If padding is applied before .head.text, virt<->phys conversions will fail.
+ */
+ASSERT(_text == (PAGE_OFFSET + TEXT_OFFSET), "HEAD is misaligned")