[Xen-changelog] [xen master] x86/PV: properly populate descriptor tables

[patchbot@xxxxxxx]

commit cf6d39f81992c29a637c603dbabf1e21a0ea563f
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Sep 25 09:05:29 2015 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Sep 25 09:05:29 2015 +0200

    x86/PV: properly populate descriptor tables
    
    Us extending the GDT limit past the Xen descriptors so far meant that
    guests (including user mode programs) accessing any descriptor table
    slot above the original OS'es limit but below the first Xen descriptor
    caused a #PF, converted to a #GP in our #PF handler. Which is quite
    different from the native behavior, where some of such accesses (LAR
    and LSL) don't fault. Mimic that behavior by mapping a blank page into
    unused slots.
    
    While not strictly required, treat the LDT the same for consistency.
    
    Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/mm.c |   21 ++++++++++++---------
 1 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 202ff76..327b837 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -502,12 +502,13 @@ void update_cr3(struct vcpu *v)
     make_cr3(v, cr3_mfn);
 }
 
+static const char __section(".bss.page_aligned") zero_page[PAGE_SIZE];
 
 static void invalidate_shadow_ldt(struct vcpu *v, int flush)
 {
     l1_pgentry_t *pl1e;
-    int i;
-    unsigned long pfn;
+    unsigned int i;
+    unsigned long pfn, zero_pfn = PFN_DOWN(__pa(zero_page));
     struct page_info *page;
 
     BUG_ON(unlikely(in_irq()));
@@ -523,8 +524,9 @@ static void invalidate_shadow_ldt(struct vcpu *v, int flush)
     for ( i = 16; i < 32; i++ )
     {
         pfn = l1e_get_pfn(pl1e[i]);
-        if ( pfn == 0 ) continue;
-        l1e_write(&pl1e[i], l1e_empty());
+        if ( !(l1e_get_flags(pl1e[i]) & _PAGE_PRESENT) || pfn == zero_pfn )
+            continue;
+        l1e_write(&pl1e[i], l1e_from_pfn(zero_pfn, __PAGE_HYPERVISOR_RO));
         page = mfn_to_page(pfn);
         ASSERT_PAGE_IS_TYPE(page, PGT_seg_desc_page);
         ASSERT_PAGE_IS_DOMAIN(page, v->domain);
@@ -4420,16 +4422,17 @@ long do_update_va_mapping_otherdomain(unsigned long va, 
u64 val64,
 void destroy_gdt(struct vcpu *v)
 {
     l1_pgentry_t *pl1e;
-    int i;
-    unsigned long pfn;
+    unsigned int i;
+    unsigned long pfn, zero_pfn = PFN_DOWN(__pa(zero_page));
 
     v->arch.pv_vcpu.gdt_ents = 0;
     pl1e = gdt_ldt_ptes(v->domain, v);
     for ( i = 0; i < FIRST_RESERVED_GDT_PAGE; i++ )
     {
-        if ( (pfn = l1e_get_pfn(pl1e[i])) != 0 )
+        pfn = l1e_get_pfn(pl1e[i]);
+        if ( (l1e_get_flags(pl1e[i]) & _PAGE_PRESENT) && pfn != zero_pfn )
             put_page_and_type(mfn_to_page(pfn));
-        l1e_write(&pl1e[i], l1e_empty());
+        l1e_write(&pl1e[i], l1e_from_pfn(zero_pfn, __PAGE_HYPERVISOR_RO));
         v->arch.pv_vcpu.gdt_frames[i] = 0;
     }
 }
@@ -4442,7 +4445,7 @@ long set_gdt(struct vcpu *v,
     struct domain *d = v->domain;
     l1_pgentry_t *pl1e;
     /* NB. There are 512 8-byte entries per GDT page. */
-    int i, nr_pages = (entries + 511) / 512;
+    unsigned int i, nr_pages = (entries + 511) / 512;
 
     if ( entries > FIRST_RESERVED_GDT_ENTRY )
         return -EINVAL;
--
generated by git-patchbot for /home/xen/git/xen.git#master

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