[xen staging] x86/boot: Adjust .text/.rodata/etc permissions in one place

[patchbot@xxxxxxx]

commit 8de86b5cd4353bf2cc415e4563f973f071b4e8a3
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Nov 29 20:04:11 2021 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Thu Dec 2 20:02:55 2021 +0000

    x86/boot: Adjust .text/.rodata/etc permissions in one place
    
    At the moment, we have two locations selecting restricted permissions, not
    very far apart on boot, dependent on opposite answers from 
using_2M_mapping().
    The later location however can shatter superpages if needed, while the 
former
    cannot.
    
    Collect together all the permission adjustments at the slightly later point 
in
    boot, as we likely need to shatter a superpage to support __ro_after_init.
    
    No functional change.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/setup.c | 74 ++++++++++++----------------------------------------
 1 file changed, 16 insertions(+), 58 deletions(-)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 0e0e706404..f5c15e45d6 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1281,55 +1281,16 @@ void __init noreturn __start_xen(unsigned long mbi_p)
                 }
             }
 
-            BUG_ON(using_2M_mapping() &&
-                   l2_table_offset((unsigned long)_erodata) ==
-                   l2_table_offset((unsigned long)_stext));
-
             /* Walk l2_xenmap[], relocating 2M superpage leaves. */
             pl2e = __va(__pa(l2_xenmap));
             for ( i = 0; i < L2_PAGETABLE_ENTRIES; i++, pl2e++ )
             {
-                unsigned int flags;
-
                 if ( !(l2e_get_flags(*pl2e) & _PAGE_PRESENT) ||
                      !(l2e_get_flags(*pl2e) & _PAGE_PSE) ||
                      (l2e_get_pfn(*pl2e) >= pte_update_limit) )
                     continue;
 
-                if ( !using_2M_mapping() )
-                {
-                    *pl2e = l2e_from_intpte(l2e_get_intpte(*pl2e) +
-                                            xen_phys_start);
-                    continue;
-                }
-
-                if ( i < l2_table_offset((unsigned long)&__2M_text_end) )
-                {
-                    flags = PAGE_HYPERVISOR_RX | _PAGE_PSE;
-                }
-                else if ( i >= l2_table_offset((unsigned 
long)&__2M_rodata_start) &&
-                          i <  l2_table_offset((unsigned 
long)&__2M_rodata_end) )
-                {
-                    flags = PAGE_HYPERVISOR_RO | _PAGE_PSE;
-                }
-                else if ( i >= l2_table_offset((unsigned 
long)&__2M_init_start) &&
-                          i <  l2_table_offset((unsigned long)&__2M_init_end) )
-                {
-                    flags = PAGE_HYPERVISOR_RWX | _PAGE_PSE;
-                }
-                else if ( (i >= l2_table_offset((unsigned 
long)&__2M_rwdata_start) &&
-                           i <  l2_table_offset((unsigned 
long)&__2M_rwdata_end)) )
-                {
-                    flags = PAGE_HYPERVISOR_RW | _PAGE_PSE;
-                }
-                else
-                {
-                    *pl2e = l2e_empty();
-                    continue;
-                }
-
-                *pl2e = l2e_from_paddr(
-                    l2e_get_paddr(*pl2e) + xen_phys_start, flags);
+                *pl2e = l2e_from_intpte(l2e_get_intpte(*pl2e) + 
xen_phys_start);
             }
 
             /* Re-sync the stack and then switch to relocated pagetables. */
@@ -1572,31 +1533,28 @@ void __init noreturn __start_xen(unsigned long mbi_p)
 #endif
 
     /*
-     * If not using 2M mappings to gain suitable pagetable permissions
-     * directly from the relocation above, remap the code/data
-     * sections with decreased permissions.
+     * All Xen mappings are currently RWX 2M superpages.  Restrict to:
+     *   text          - RX
+     *   rodata        - RO
+     *   init          - keep RWX, discarded entirely later
+     *   data/bss      - RW
      */
-    if ( !using_2M_mapping() )
-    {
-        /* Mark .text as RX (avoiding the first 2M superpage). */
-        modify_xen_mappings(XEN_VIRT_START + MB(2),
-                            (unsigned long)&__2M_text_end,
-                            PAGE_HYPERVISOR_RX);
+    modify_xen_mappings((unsigned long)&_start,
+                        (unsigned long)&__2M_text_end,
+                        PAGE_HYPERVISOR_RX);
 
-        /* Mark .rodata as RO. */
-        modify_xen_mappings((unsigned long)&__2M_rodata_start,
-                            (unsigned long)&__2M_rodata_end,
-                            PAGE_HYPERVISOR_RO);
+    modify_xen_mappings((unsigned long)&__2M_rodata_start,
+                        (unsigned long)&__2M_rodata_end,
+                        PAGE_HYPERVISOR_RO);
 
-        /* Mark .data and .bss as RW. */
-        modify_xen_mappings((unsigned long)&__2M_rwdata_start,
-                            (unsigned long)&__2M_rwdata_end,
-                            PAGE_HYPERVISOR_RW);
+    modify_xen_mappings((unsigned long)&__2M_rwdata_start,
+                        (unsigned long)&__2M_rwdata_end,
+                        PAGE_HYPERVISOR_RW);
 
+    if ( !using_2M_mapping() )
         /* Drop the remaining mappings in the shattered superpage. */
         destroy_xen_mappings((unsigned long)&__2M_rwdata_end,
                              ROUNDUP((unsigned long)&__2M_rwdata_end, MB(2)));
-    }
 
     nr_pages = 0;
     for ( i = 0; i < e820.nr_map; i++ )
--
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