From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Mon, 16 Oct 2017 13:20:07 +0000 (+0000)
Subject: xen/pv: Construct d0v0's GDT properly
X-Git-Tag: archive/raspbian/4.11.1-1+rpi1~1^2~66^2~990
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=08f27f4468eedbeccaac9fdda4ef732247efd74e;p=xen.git

xen/pv: Construct d0v0's GDT properly

c/s cf6d39f8199 "x86/PV: properly populate descriptor tables" changed the GDT
to reference zero_page for intermediate frames between the guest and Xen
frames.

Because dom0_construct_pv() doesn't call arch_set_info_guest(), some bits of
initialisation are missed, including the pv_destroy_gdt() which initially
fills the references to zero_page.

In practice, this means there is a window between starting and the first call
to HYPERCALL_set_gdt() were lar/lsl/verr/verw suffer non-architectural
behaviour.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
This probably wants backporting to Xen 4.7 and later.
---

diff --git a/xen/arch/x86/pv/dom0_build.c b/xen/arch/x86/pv/dom0_build.c
index 44601d08d3..a13412efb9 100644
--- a/xen/arch/x86/pv/dom0_build.c
+++ b/xen/arch/x86/pv/dom0_build.c
@@ -18,6 +18,7 @@
 #include <asm/bzimage.h>
 #include <asm/dom0_build.h>
 #include <asm/page.h>
+#include <asm/pv/mm.h>
 #include <asm/setup.h>
 
 /* Allow ring-3 access in long mode as guest cannot use ring 1 ... */
@@ -866,6 +867,13 @@ int __init dom0_construct_pv(struct domain *d,
     regs->rsi = vstartinfo_start;
     regs->eflags = X86_EFLAGS_IF;
 
+    /*
+     * We don't call arch_set_info_guest(), so some initialisation needs doing
+     * by hand:
+     *  - Reset the GDT to reference zero_page
+     */
+    pv_destroy_gdt(v);
+
     if ( test_bit(XENFEAT_supervisor_mode_kernel, parms.f_required) )
         panic("Dom0 requires supervisor-mode execution");