From 8b9f8a7e763dfc533ce2abd5b48d1ba9f54165e2 Mon Sep 17 00:00:00 2001
From: Andrew Turner <andrew@FreeBSD.org>
Date: Wed, 12 Jun 2024 14:08:13 +0100
Subject: [PATCH] arm64: Clear td_frame when returning to userspace

When returning from an exception to userspace clear the saved td_frame.
On the next exception this should point to the frame, however this is
not guaranteed.

To ensure the trap frame pointer is either valid or NULL clear it
before returning to userspace in the EL0 synchronous exception handler.

Reviewed by:	kib, markj
Sponsored by:	Arm Ltd
Differential Revision:	https://reviews.freebsd.org/D44807

(cherry picked from commit 4eec584d79c1e8375d863c7eec7229ac7ec3f13b)
---
 sys/arm64/arm64/exception.S | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sys/arm64/arm64/exception.S b/sys/arm64/arm64/exception.S
index b1990fc7128..0df44086363 100644
--- a/sys/arm64/arm64/exception.S
+++ b/sys/arm64/arm64/exception.S
@@ -214,9 +214,11 @@ ENTRY(handle_el0_sync)
 	save_registers 0
 	ldr	x0, [x18, #PC_CURTHREAD]
 	mov	x1, sp
+	mov	x22, x0
 	str	x1, [x0, #TD_FRAME]
 	bl	do_el0_sync
 	do_ast
+	str	xzr, [x22, #TD_FRAME]
 	restore_registers 0
 	ERET
 END(handle_el0_sync)