[PATCH v3 14/17] arm64: efi: restore x18 if it was corrupted

[samitolvanen]

If we detect a corrupted x18 and SCS is enabled, restore the register
before jumping back to instrumented code. This is safe, because the
wrapper is called with preemption disabled and a separate shadow stack
is used for interrupt handling.

Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
---
 arch/arm64/kernel/efi-rt-wrapper.S | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/efi-rt-wrapper.S b/arch/arm64/kernel/efi-rt-wrapper.S
index 3fc71106cb2b..945744f16086 100644
--- a/arch/arm64/kernel/efi-rt-wrapper.S
+++ b/arch/arm64/kernel/efi-rt-wrapper.S
@@ -34,5 +34,10 @@ ENTRY(__efi_rt_asm_wrapper)
 	ldp	x29, x30, [sp], #32
 	b.ne	0f
 	ret
-0:	b	efi_handle_corrupted_x18	// tail call
+0:
+#ifdef CONFIG_SHADOW_CALL_STACK
+	/* Restore x18 before returning to instrumented code. */
+	mov	x18, x2
+#endif
+	b	efi_handle_corrupted_x18	// tail call
 ENDPROC(__efi_rt_asm_wrapper)
-- 
2.24.0.rc0.303.g954a862665-goog