[Xen-changelog] [xen stable-4.9] xen/pv: Construct d0v0's GDT properly

[patchbot@xxxxxxx]

commit 57205c489dd66bc0a2f01a64eb6e416e37cd5a0d
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Wed Dec 20 15:55:17 2017 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Dec 20 15:55:17 2017 +0100

    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@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 08f27f4468eedbeccaac9fdda4ef732247efd74e
    master date: 2017-12-01 19:03:26 +0000
---
 xen/arch/x86/pv/dom0_build.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/xen/arch/x86/pv/dom0_build.c b/xen/arch/x86/pv/dom0_build.c
index 18c19a2..52aea4d 100644
--- a/xen/arch/x86/pv/dom0_build.c
+++ b/xen/arch/x86/pv/dom0_build.c
@@ -870,6 +870,13 @@ 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
+     */
+    destroy_gdt(v);
+
     if ( test_bit(XENFEAT_supervisor_mode_kernel, parms.f_required) )
         panic("Dom0 requires supervisor-mode execution");
 
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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