From b843f9be5e77e2ff653d12965351239811a61b1c Mon Sep 17 00:00:00 2001 From: John Baldwin Date: Thu, 11 Oct 2018 18:27:19 +0000 Subject: [PATCH] Fully restore the GDTR, IDTR, and LDTR after VT-x VM exits. The VT-x VMCS only stores the base address of the GDTR and IDTR. As a result, VM exits use a fixed limit of 0xffff for the host GDTR and IDTR losing the smaller limits set in when the initial GDT is loaded on each CPU during boot. Explicitly save and restore the full GDTR and IDTR contents around VM entries and exits to restore the correct limit. Similarly, explicitly save and restore the LDT selector. VM exits always clear the host LDTR as if the LDT was loaded with a NULL selector and a userspace hypervisor is probably using a NULL selector anyway, but save and restore the LDT explicitly just to be safe. PR: 230773 Reported by: John Levon Reviewed by: kib Tested by: araujo Approved by: re (rgrimes) MFC after: 1 week --- sys/amd64/include/cpufunc.h | 9 +++++++++ sys/amd64/vmm/intel/vmx.c | 22 ++++++++++++++++++++++ 2 files changed, 31 insertions(+) diff --git a/sys/amd64/include/cpufunc.h b/sys/amd64/include/cpufunc.h index a0ea1b2f1701..e04e50cfe19f 100644 --- a/sys/amd64/include/cpufunc.h +++ b/sys/amd64/include/cpufunc.h @@ -730,6 +730,15 @@ lldt(u_short sel) __asm __volatile("lldt %0" : : "r" (sel)); } +static __inline u_short +sldt(void) +{ + u_short sel; + + __asm __volatile("sldt %0" : "=r" (sel)); + return (sel); +} + static __inline void ltr(u_short sel) { diff --git a/sys/amd64/vmm/intel/vmx.c b/sys/amd64/vmm/intel/vmx.c index 61871e9338eb..f138e57130df 100644 --- a/sys/amd64/vmm/intel/vmx.c +++ b/sys/amd64/vmm/intel/vmx.c @@ -2833,6 +2833,8 @@ vmx_run(void *arg, int vcpu, register_t rip, pmap_t pmap, struct vm_exit *vmexit; struct vlapic *vlapic; uint32_t exit_reason; + struct region_descriptor gdtr, idtr; + uint16_t ldt_sel; vmx = arg; vm = vmx->vm; @@ -2924,11 +2926,31 @@ vmx_run(void *arg, int vcpu, register_t rip, pmap_t pmap, break; } + /* + * VM exits restore the base address but not the + * limits of GDTR and IDTR. The VMCS only stores the + * base address, so VM exits set the limits to 0xffff. + * Save and restore the full GDTR and IDTR to restore + * the limits. + * + * The VMCS does not save the LDTR at all, and VM + * exits clear LDTR as if a NULL selector were loaded. + * The userspace hypervisor probably doesn't use a + * LDT, but save and restore it to be safe. + */ + sgdt(&gdtr); + sidt(&idtr); + ldt_sel = sldt(); + vmx_run_trace(vmx, vcpu); vmx_dr_enter_guest(vmxctx); rc = vmx_enter_guest(vmxctx, vmx, launched); vmx_dr_leave_guest(vmxctx); + bare_lgdt(&gdtr); + lidt(&idtr); + lldt(ldt_sel); + /* Collect some information for VM exit processing */ vmexit->rip = rip = vmcs_guest_rip(); vmexit->inst_length = vmexit_instruction_length();