[xen master] x86: relax GDT check in arch_set_info_guest()

[patchbot@xxxxxxx]

commit ded6e9d514902be17069b59b335c3165c601f86a
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri May 22 16:09:54 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri May 22 16:09:54 2020 +0200

    x86: relax GDT check in arch_set_info_guest()
    
    It is wrong for us to check frames beyond the guest specified limit
    (in the compat case another loop bound is already correct).
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/domain.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 2e5717b983..6402b09993 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -840,6 +840,7 @@ int arch_set_info_guest(
 #ifdef CONFIG_PV
     mfn_t cr3_mfn;
     struct page_info *cr3_page = NULL;
+    unsigned int nr_gdt_frames;
     int rc = 0;
 #endif
 
@@ -957,6 +958,10 @@ int arch_set_info_guest(
     /* Ensure real hardware interrupts are enabled. */
     v->arch.user_regs.eflags |= X86_EFLAGS_IF;
 
+    nr_gdt_frames = DIV_ROUND_UP(c(gdt_ents), 512);
+    if ( nr_gdt_frames > ARRAY_SIZE(v->arch.pv.gdt_frames) )
+        return -EINVAL;
+
     if ( !v->is_initialised )
     {
         if ( !compat && !(flags & VGCF_in_kernel) && !c.nat->ctrlreg[1] )
@@ -988,9 +993,9 @@ int arch_set_info_guest(
             fail = compat_pfn_to_cr3(pfn) != c.cmp->ctrlreg[3];
         }
 
-        for ( i = 0; i < ARRAY_SIZE(v->arch.pv.gdt_frames); ++i )
-            fail |= v->arch.pv.gdt_frames[i] != c(gdt_frames[i]);
         fail |= v->arch.pv.gdt_ents != c(gdt_ents);
+        for ( i = 0; !fail && i < nr_gdt_frames; ++i )
+            fail = v->arch.pv.gdt_frames[i] != c(gdt_frames[i]);
 
         fail |= v->arch.pv.ldt_base != c(ldt_base);
         fail |= v->arch.pv.ldt_ents != c(ldt_ents);
@@ -1095,12 +1100,8 @@ int arch_set_info_guest(
     else
     {
         unsigned long gdt_frames[ARRAY_SIZE(v->arch.pv.gdt_frames)];
-        unsigned int nr_frames = DIV_ROUND_UP(c.cmp->gdt_ents, 512);
-
-        if ( nr_frames > ARRAY_SIZE(v->arch.pv.gdt_frames) )
-            return -EINVAL;
 
-        for ( i = 0; i < nr_frames; ++i )
+        for ( i = 0; i < nr_gdt_frames; ++i )
             gdt_frames[i] = c.cmp->gdt_frames[i];
 
         rc = (int)pv_set_gdt(v, gdt_frames, c.cmp->gdt_ents);
--
generated by git-patchbot for /home/xen/git/xen.git#master