x86/xen: add central hypercall functions

Add generic hypercall functions usable for all normal (i.e. not iret)
hypercalls. Depending on the guest type and the processor vendor
different functions need to be used due to the to be used instruction
for entering the hypervisor:

- PV guests need to use syscall
- HVM/PVH guests on Intel need to use vmcall
- HVM/PVH guests on AMD and Hygon need to use vmmcall

As PVH guests need to issue hypercalls very early during boot, there
is a 4th hypercall function needed for HVM/PVH which can be used on
Intel and AMD processors. It will check the vendor type and then set
the Intel or AMD specific function to use via static_call().

This is part of XSA-466 / CVE-2024-53241.

Reported-by: Andrew Cooper <[email protected]>
Signed-off-by: Juergen Gross <[email protected]>
Co-developed-by: Peter Zijlstra <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index 24d2957a4726..973a74fc966a 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -300,6 +300,10 @@ static uint32_t __init xen_platform_hvm(void)
 	if (xen_pv_domain())
 		return 0;
 
+	/* Set correct hypercall function. */
+	if (xen_domain)
+		xen_hypercall_setfunc();
+
 	if (xen_pvh_domain() && nopv) {
 		/* Guest booting via the Xen-PVH boot entry goes here */
 		pr_info("\"nopv\" parameter is ignored in PVH guest\n");