From 9999d3c6d93e90c732a205fd031a3f0a4c2294c0 Mon Sep 17 00:00:00 2001
From: kettenis <kettenis@openbsd.org>
Date: Tue, 5 Mar 2024 18:42:20 +0000
Subject: [PATCH] Tighten up BTCFI by flipping the bits that make PACIASP and
 PACIBSP behave like BTI c instead of BTI jc.

ok deraadt@, tobhe@
---
 sys/arch/arm64/arm64/cpu.c      | 9 ++++++++-
 sys/arch/arm64/include/armreg.h | 4 +++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/sys/arch/arm64/arm64/cpu.c b/sys/arch/arm64/arm64/cpu.c
index 34444bda98c..b11bf3699ac 100644
--- a/sys/arch/arm64/arm64/cpu.c
+++ b/sys/arch/arm64/arm64/cpu.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: cpu.c,v 1.107 2024/03/01 15:57:43 kettenis Exp $	*/
+/*	$OpenBSD: cpu.c,v 1.108 2024/03/05 18:42:20 kettenis Exp $	*/
 
 /*
  * Copyright (c) 2016 Dale Rahn <drahn@dalerahn.com>
@@ -1042,6 +1042,13 @@ cpu_init(void)
 		WRITE_SPECIALREG(sctlr_el1, sctlr);
 	}
 
+	/* Enable strict BTI compatibility for PACIASP and PACIBSP. */
+	if (ID_AA64PFR1_BT(cpu_id_aa64pfr1) >= ID_AA64PFR1_BT_IMPL) {
+		sctlr = READ_SPECIALREG(sctlr_el1);
+		sctlr |= SCTLR_BT0 | SCTLR_BT1;
+		WRITE_SPECIALREG(sctlr_el1, sctlr);
+	}
+
 	/* Initialize debug registers. */
 	WRITE_SPECIALREG(mdscr_el1, DBG_MDSCR_TDCC);
 	WRITE_SPECIALREG(oslar_el1, 0);
diff --git a/sys/arch/arm64/include/armreg.h b/sys/arch/arm64/include/armreg.h
index 91d2f402a89..59983aa13e0 100644
--- a/sys/arch/arm64/include/armreg.h
+++ b/sys/arch/arm64/include/armreg.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: armreg.h,v 1.30 2023/11/29 23:32:16 kettenis Exp $ */
+/* $OpenBSD: armreg.h,v 1.31 2024/03/05 18:42:20 kettenis Exp $ */
 /*-
  * Copyright (c) 2013, 2014 Andrew Turner
  * Copyright (c) 2015 The FreeBSD Foundation
@@ -656,6 +656,8 @@
 #define	SCTLR_EnDA	0x0000000008000000
 #define	SCTLR_EnIB	0x0000000040000000
 #define	SCTLR_EnIA	0x0000000080000000
+#define	SCTLR_BT0	0x0000000800000000
+#define	SCTLR_BT1	0x0000001000000000
 
 /* SPSR_EL1 */
 /*
-- 
2.20.1