From 7dfdc4ecaff5fdabe7a7c328385ffa6e42e169db Mon Sep 17 00:00:00 2001
From: kettenis <kettenis@openbsd.org>
Date: Fri, 31 Mar 2023 18:45:05 +0000
Subject: [PATCH] Call entry point of the executable through register x17. 
 This allows it to be a normal C function that starts with "bti c" when BTI
 contro flow integretry enforcement is in place.  Add "bti c" to
 _dl_bind_start().

Remove unused _rtld_tlsdesc() function to avoid having to add "bti c" to it.

ok deraadt@
---
 libexec/ld.so/aarch64/ldasm.S | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/libexec/ld.so/aarch64/ldasm.S b/libexec/ld.so/aarch64/ldasm.S
index 9da1c9f20f3..e148a372632 100644
--- a/libexec/ld.so/aarch64/ldasm.S
+++ b/libexec/ld.so/aarch64/ldasm.S
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ldasm.S,v 1.8 2019/05/10 13:29:21 guenther Exp $ */
+/*	$OpenBSD: ldasm.S,v 1.9 2023/03/31 18:45:05 kettenis Exp $ */
 
 /*
  * Copyright (c) 2016 Dale Rahn
@@ -57,6 +57,7 @@ _dl_start:
 	ldr	x2, [x20, #7*8]			// loff from dl_data
 	mov	x3, x20				// dl_data
 	bl	_dl_boot
+	mov	x17, x0
 
 	mov	sp, x29				// move stack back
 	mov	x29, xzr			// clear frame back pointer
@@ -65,7 +66,7 @@ _dl_start:
 	adrp	x8, :got:_dl_dtors
 	ldr	x2, [x8, :got_lo12:_dl_dtors]
 
-	br	x0
+	br	x17
 END(_dl_start)
 
 ENTRY(_dl_bind_start)
@@ -75,7 +76,8 @@ ENTRY(_dl_bind_start)
 	 * return address and pointer to pltgot entry for this
 	 * relocation are on the stack
 	 */
-	mov x17, sp
+	bti	c
+	mov	x17, sp
 
 	// save parameter/result registers
 	stp	x0, x1, [sp, #-16]!
@@ -109,10 +111,3 @@ ENTRY(_dl_bind_start)
 	ldp	xzr, x30, [sp], #16
 	br	x17
 END(_dl_bind_start)
-
-ENTRY(_rtld_tlsdesc)
-	RETGUARD_SETUP(_rtld_tlsdesc, x15)
-	ldr	x0, [x0, #8]
-	RETGUARD_CHECK(_rtld_tlsdesc, x15)
-	ret
-END(_rtld_tlsdesc)
-- 
2.20.1