4 files changed, 11 insertions, 12 deletions

diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index bc359dd2f7f6..85e23bb7b34e 100644
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -21,6 +21,8 @@ static inline void fill_ldt(struct desc_struct *desc, const struct user_desc *in
 
         desc->type              = (info->read_exec_only ^ 1) << 1;
         desc->type             |= info->contents << 2;
+        /* Set the ACCESS bit so it can be mapped RO */
+        desc->type             |= 1;
 
         desc->s                 = 1;
         desc->dpl               = 0x3;
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index 9629c5d8267a..579cc4a66fdf 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -158,7 +158,12 @@ map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot)
                 ptep = get_locked_pte(mm, va, &ptl);
                 if (!ptep)
                         return -ENOMEM;
-                pte = pfn_pte(pfn, __pgprot(__PAGE_KERNEL & ~_PAGE_GLOBAL));
+                /*
+                 * Map it RO so the easy to find address is not a primary
+                 * target via some kernel interface which misses a
+                 * permission check.
+                 */
+                pte = pfn_pte(pfn, __pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL));
                 set_pte_at(mm, va, ptep, pte);
                 pte_unmap_unlock(ptep, ptl);
         }
diff --git a/arch/x86/kernel/tls.c b/arch/x86/kernel/tls.c
index 9a9c9b076955..a5b802a12212 100644
--- a/arch/x86/kernel/tls.c
+++ b/arch/x86/kernel/tls.c
@@ -93,17 +93,10 @@ static void set_tls_desc(struct task_struct *p, int idx,
         cpu = get_cpu();
 
         while (n-- > 0) {
-                if (LDT_empty(info) || LDT_zero(info)) {
+                if (LDT_empty(info) || LDT_zero(info))
                         memset(desc, 0, sizeof(*desc));
-                } else {
+                else
                         fill_ldt(desc, info);
-
-                        /*
-                         * Always set the accessed bit so that the CPU
-                         * doesn't try to write to the (read-only) GDT.
-                         */
-                        desc->type |= 1;
-                }
                 ++info;
                 ++desc;
         }
diff --git a/tools/testing/selftests/x86/ldt_gdt.c b/tools/testing/selftests/x86/ldt_gdt.c
index 0304ffb714f2..1aef72df20a1 100644
--- a/tools/testing/selftests/x86/ldt_gdt.c
+++ b/tools/testing/selftests/x86/ldt_gdt.c
@@ -122,8 +122,7 @@ static void check_valid_segment(uint16_t index, int ldt,
          * NB: Different Linux versions do different things with the
          * accessed bit in set_thread_area().
          */
-        if (ar != expected_ar &&
-            (ldt || ar != (expected_ar | AR_ACCESSED))) {
+        if (ar != expected_ar && ar != (expected_ar | AR_ACCESSED)) {
                 printf("[FAIL]\t%s entry %hu has AR 0x%08X but expected 0x%08X\n",
                        (ldt ? "LDT" : "GDT"), index, ar, expected_ar);
                 nerrs++;