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

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 7ab6b358cc35194079f7d7613b246608afd46eaf..a5004a5b7aa4a7e951c80fd4adf9bce805576c28 100644 (file)
--- 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 7218fefc6ac9510c9477b595165ea46340b16301..9129a917203e998f9287b4679a2716f466774475 100644 (file)
--- 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