From 6559a686ae77bca2539d826120c9f3bd0d75cdf8 Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Date: Mon, 8 Aug 2016 23:14:33 -0400
Subject: [PATCH] arm/mm: Introduce modify_xen_mappings

Which is only used by Livepatch code. The purpose behind
this call is to modify the page table entries flags.

Specifically the .ro and .nx flags. The current mechanism
puts cache attributes in the flags and the .ro and .nx are
locked down and assumed to be .ro=0, nx=1.

Livepatch needs .nx=0 and also .ro to be set to 1.

We introduce a new 'flags' where various bits determine
whether .ro and .nx bits are set or cleared. We can't use
an enum as the function prototype would diverge from x86.

Reviewed-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 xen/arch/arm/mm.c          | 27 ++++++++++++++++++++++++---
 xen/include/asm-arm/page.h | 11 +++++++++++
 2 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 7ae9f6369a..07e2037e9b 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -836,6 +836,7 @@ static int create_xen_table(lpae_t *entry)
 enum xenmap_operation {
     INSERT,
     REMOVE,
+    MODIFY,
     RESERVE
 };
 
@@ -881,14 +882,28 @@ static int create_xen_entries(enum xenmap_operation op,
                 pte.pt.table = 1;
                 write_pte(&third[third_table_offset(addr)], pte);
                 break;
+            case MODIFY:
             case REMOVE:
                 if ( !third[third_table_offset(addr)].pt.valid )
                 {
-                    printk("create_xen_entries: trying to remove a non-existing mapping addr=%lx\n",
-                           addr);
+                    printk("create_xen_entries: trying to %s a non-existing mapping addr=%lx\n",
+                           op == REMOVE ? "remove" : "modify", addr);
                     return -EINVAL;
                 }
-                pte.bits = 0;
+                if ( op == REMOVE )
+                    pte.bits = 0;
+                else
+                {
+                    pte = third[third_table_offset(addr)];
+                    pte.pt.ro = PTE_RO_MASK(ai);
+                    pte.pt.xn = PTE_NX_MASK(ai);
+                    if ( !pte.pt.ro && !pte.pt.xn )
+                    {
+                        printk("create_xen_entries: Incorrect combination for addr=%lx\n",
+                               addr);
+                        return -EINVAL;
+                    }
+                }
                 write_pte(&third[third_table_offset(addr)], pte);
                 break;
             default:
@@ -922,6 +937,12 @@ int destroy_xen_mappings(unsigned long v, unsigned long e)
     return create_xen_entries(REMOVE, v, 0, (e - v) >> PAGE_SHIFT, 0);
 }
 
+int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int flags)
+{
+    ASSERT((flags & (PTE_NX | PTE_RO)) == flags);
+    return create_xen_entries(MODIFY, s, 0, (e - s) >> PAGE_SHIFT, flags);
+}
+
 enum mg { mg_clear, mg_ro, mg_rw, mg_rx };
 static void set_pte_flags_on_range(const char *p, unsigned long l, enum mg mg)
 {
diff --git a/xen/include/asm-arm/page.h b/xen/include/asm-arm/page.h
index 05d9f82d0d..015ed6307a 100644
--- a/xen/include/asm-arm/page.h
+++ b/xen/include/asm-arm/page.h
@@ -65,6 +65,17 @@
 #define PAGE_HYPERVISOR_NOCACHE (DEV_SHARED)
 #define PAGE_HYPERVISOR_WC      (DEV_WC)
 
+/*
+ * Defines for changing the hypervisor PTE .ro and .nx bits. This is only to be
+ * used with modify_xen_mappings.
+ */
+#define _PTE_NX_BIT     0U
+#define _PTE_RO_BIT     1U
+#define PTE_NX          (1U << _PTE_NX_BIT)
+#define PTE_RO          (1U << _PTE_RO_BIT)
+#define PTE_NX_MASK(x)  (((x) >> _PTE_NX_BIT) & 0x1U)
+#define PTE_RO_MASK(x)  (((x) >> _PTE_RO_BIT) & 0x1U)
+
 /*
  * Stage 2 Memory Type.
  *
-- 
2.30.2