[PATCH v3 2/4] arm64: Trap PIE builds early if load address is not 4K aligned

[Edgar E. Iglesias]

From: "Edgar E. Iglesias" <edgar.iglesias at xilinx.com>

PIE requires a 4K aligned load address. If this is not met, trap
the startup sequence in a WFI loop rather than running into obscure
failures.

Tested-by: Michal Simek <michal.simek at xilinx.com>
Suggested-by: André Przywara <andre.przywara at arm.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias at xilinx.com>
---
 arch/arm/cpu/armv8/start.S | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/arch/arm/cpu/armv8/start.S b/arch/arm/cpu/armv8/start.S
index 002698b501..85baebc5f7 100644
--- a/arch/arm/cpu/armv8/start.S
+++ b/arch/arm/cpu/armv8/start.S
@@ -59,6 +59,23 @@ reset:
 save_boot_params_ret:
 
 #if CONFIG_POSITION_INDEPENDENT
+	/* Verify that we're 4K aligned.  */
+	adr	x0, _start
+	ands	x0, x0, #0xfff
+	b.eq	1f
+0:
+	/*
+	 * FATAL, can't continue.
+	 * U-Boot needs to be loaded at a 4K aligned address.
+	 *
+	 * We use ADRP and ADD to load some symbol addresses during startup.
+	 * The ADD uses an absolute (non pc-relative) lo12 relocation
+	 * thus requiring 4K alignment.
+	 */
+	wfi
+	b	0b
+1:
+
 	/*
 	 * Fix .rela.dyn relocations. This allows U-Boot to be loaded to and
 	 * executed at a different address than it was linked at.
-- 
2.25.1