1 files changed, 87 insertions, 0 deletions
diff --git a/arch/arm64/kernel/efi-rt-wrapper.S b/arch/arm64/kernel/efi-rt-wrapper.S
new file mode 100644
index 000000000..e8ae80366
--- /dev/null
+++ b/arch/arm64/kernel/efi-rt-wrapper.S
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2018 Linaro Ltd <ard.biesheuvel@linaro.org>
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+SYM_FUNC_START(__efi_rt_asm_wrapper)
+	stp	x29, x30, [sp, #-112]!
+	mov	x29, sp
+
+	/*
+	 * Register x18 is designated as the 'platform' register by the AAPCS,
+	 * which means firmware running at the same exception level as the OS
+	 * (such as UEFI) should never touch it.
+	 */
+	stp	x1, x18, [sp, #16]
+
+	/*
+	 * Preserve all callee saved registers and preserve the stack pointer
+	 * value at the base of the EFI runtime stack so we can recover from
+	 * synchronous exceptions occurring while executing the firmware
+	 * routines.
+	 */
+	stp	x19, x20, [sp, #32]
+	stp	x21, x22, [sp, #48]
+	stp	x23, x24, [sp, #64]
+	stp	x25, x26, [sp, #80]
+	stp	x27, x28, [sp, #96]
+
+	ldr_l	x16, efi_rt_stack_top
+	mov	sp, x16
+	stp	x18, x29, [sp, #-16]!
+
+	/*
+	 * We are lucky enough that no EFI runtime services take more than
+	 * 5 arguments, so all are passed in registers rather than via the
+	 * stack.
+	 */
+	mov	x8, x0
+	mov	x0, x2
+	mov	x1, x3
+	mov	x2, x4
+	mov	x3, x5
+	mov	x4, x6
+	blr	x8
+
+	mov	x16, sp
+	mov	sp, x29
+	str	xzr, [x16, #8]			// clear recorded task SP value
+
+	ldp	x1, x2, [sp, #16]
+	cmp	x2, x18
+	ldp	x29, x30, [sp], #112
+	b.ne	0f
+	ret
+0:
+	/*
+	 * With CONFIG_SHADOW_CALL_STACK, the kernel uses x18 to store a
+	 * shadow stack pointer, which we need to restore before returning to
+	 * potentially instrumented code. This is safe because the wrapper is
+	 * called with preemption disabled and a separate shadow stack is used
+	 * for interrupts.
+	 */
+#ifdef CONFIG_SHADOW_CALL_STACK
+	ldr_l	x18, efi_rt_stack_top
+	ldr	x18, [x18, #-16]
+#endif
+
+	b	efi_handle_corrupted_x18	// tail call
+SYM_FUNC_END(__efi_rt_asm_wrapper)
+
+SYM_CODE_START(__efi_rt_asm_recover)
+	mov	sp, x30
+
+	ldr_l	x16, efi_rt_stack_top		// clear recorded task SP value
+	str	xzr, [x16, #-8]
+
+	ldp	x19, x20, [sp, #32]
+	ldp	x21, x22, [sp, #48]
+	ldp	x23, x24, [sp, #64]
+	ldp	x25, x26, [sp, #80]
+	ldp	x27, x28, [sp, #96]
+	ldp	x29, x30, [sp], #112
+	ret
+SYM_CODE_END(__efi_rt_asm_recover)