From bc3c2f6195973bddd45dfa99715740ad80b376fd Mon Sep 17 00:00:00 2001
From: anton <anton@openbsd.org>
Date: Wed, 5 Jul 2023 18:23:10 +0000
Subject: [PATCH] The hypercall page populated with instructions by the
 hypervisor is not IBT compatible due to lack of endbr64. Replace the indirect
 call with a new hv_hypercall_trampoline() routine which jumps to the
 hypercall page without any indirection.

Allows me to boot OpenBSD using Hyper-V on Windows 11 again.

ok guenther@
---
 sys/arch/amd64/amd64/locore.S | 24 ++++++++++++++++--------
 sys/dev/pv/hyperv.c           |  5 ++---
 2 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/sys/arch/amd64/amd64/locore.S b/sys/arch/amd64/amd64/locore.S
index 677c816d6f9..ec41559e6bf 100644
--- a/sys/arch/amd64/amd64/locore.S
+++ b/sys/arch/amd64/amd64/locore.S
@@ -1,4 +1,4 @@
-/*	$OpenBSD: locore.S,v 1.134 2023/04/17 00:14:59 deraadt Exp $	*/
+/*	$OpenBSD: locore.S,v 1.135 2023/07/05 18:23:10 anton Exp $	*/
 /*	$NetBSD: locore.S,v 1.13 2004/03/25 18:33:17 drochner Exp $	*/
 
 /*
@@ -1149,20 +1149,28 @@ NENTRY(rdmsr_resume)
 	lfence
 END(rdmsr_safe)
 
-#if NXEN > 0
+#if NHYPERV > 0
+/* uint64_t hv_hypercall_trampoline(uint64_t control, paddr_t input, paddr_t output) */
+NENTRY(hv_hypercall_trampoline)
+	endbr64
+	mov	%rdx, %r8
+	mov	%rsi, %rdx
+	mov	%rdi, %rcx
+	jmp	hv_hypercall_page
+END(hv_hypercall_trampoline)
 	/* Hypercall page needs to be page aligned */
 	.text
 	.align	NBPG, 0xcc
-	.globl	xen_hypercall_page
-xen_hypercall_page:
+	.globl	hv_hypercall_page
+hv_hypercall_page:
 	.skip	0x1000, 0xcc
-#endif /* NXEN > 0 */
+#endif /* NHYPERV > 0 */
 
-#if NHYPERV > 0
+#if NXEN > 0
 	/* Hypercall page needs to be page aligned */
 	.text
 	.align	NBPG, 0xcc
-	.globl	hv_hypercall_page
-hv_hypercall_page:
+	.globl	xen_hypercall_page
+xen_hypercall_page:
 	.skip	0x1000, 0xcc
 #endif /* NXEN > 0 */
diff --git a/sys/dev/pv/hyperv.c b/sys/dev/pv/hyperv.c
index 08a713d814d..da9bf3ae6d7 100644
--- a/sys/dev/pv/hyperv.c
+++ b/sys/dev/pv/hyperv.c
@@ -407,9 +407,8 @@ hv_hypercall(struct hv_softc *sc, uint64_t control, void *input,
 	}
 
 #ifdef __amd64__
-	__asm__ volatile ("mov %0, %%r8" : : "r" (output_pa) : "r8");
-	__asm__ volatile ("call *%3" : "=a" (status) : "c" (control),
-	    "d" (input_pa), "m" (sc->sc_hc));
+	extern uint64_t hv_hypercall_trampoline(uint64_t, paddr_t, paddr_t);
+	status = hv_hypercall_trampoline(control, input_pa, output_pa);
 #else  /* __i386__ */
 	{
 		uint32_t control_hi = control >> 32;
-- 
2.20.1