arm64: vdso: put vdso datapage in a separate vma

The VDSO datapage doesn't need to be executable (no code there) or
CoW-able (the kernel writes the page, so a private copy is totally
useless).

This patch moves the datapage into its own VMA, identified as "[vvar]"
in /proc/<pid>/maps.

Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 26 insertions, 8 deletions

diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index 50384fec56c4..84cafbc3eb54 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -138,11 +138,12 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
                                 int uses_interp)
 {
         struct mm_struct *mm = current->mm;
-        unsigned long vdso_base, vdso_mapping_len;
+        unsigned long vdso_base, vdso_text_len, vdso_mapping_len;
         int ret;
 
+        vdso_text_len = vdso_pages << PAGE_SHIFT;
         /* Be sure to map the data page */
-        vdso_mapping_len = (vdso_pages + 1) << PAGE_SHIFT;
+        vdso_mapping_len = vdso_text_len + PAGE_SIZE;
 
         down_write(&mm->mmap_sem);
         vdso_base = get_unmapped_area(NULL, 0, vdso_mapping_len, 0, 0);
@@ -152,35 +153,52 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
         }
         mm->context.vdso = (void *)vdso_base;
 
-        ret = install_special_mapping(mm, vdso_base, vdso_mapping_len,
+        ret = install_special_mapping(mm, vdso_base, vdso_text_len,
                                       VM_READ|VM_EXEC|
                                       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
                                       vdso_pagelist);
-        if (ret) {
-                mm->context.vdso = NULL;
+        if (ret)
+                goto up_fail;
+
+        vdso_base += vdso_text_len;
+        ret = install_special_mapping(mm, vdso_base, PAGE_SIZE,
+                                      VM_READ|VM_MAYREAD,
+                                      vdso_pagelist + vdso_pages);
+        if (ret)
                 goto up_fail;
-        }
 
-up_fail:
         up_write(&mm->mmap_sem);
+        return 0;
 
+up_fail:
+        mm->context.vdso = NULL;
+        up_write(&mm->mmap_sem);
         return ret;
 }
 
 const char *arch_vma_name(struct vm_area_struct *vma)
 {
+        unsigned long vdso_text;
+
+        if (!vma->vm_mm)
+                return NULL;
+
+        vdso_text = (unsigned long)vma->vm_mm->context.vdso;
+
         /*
          * We can re-use the vdso pointer in mm_context_t for identifying
          * the vectors page for compat applications. The vDSO will always
          * sit above TASK_UNMAPPED_BASE and so we don't need to worry about
          * it conflicting with the vectors base.
          */
-        if (vma->vm_mm && vma->vm_start == (long)vma->vm_mm->context.vdso) {
+        if (vma->vm_start == vdso_text) {
 #ifdef CONFIG_COMPAT
                 if (vma->vm_start == AARCH32_VECTORS_BASE)
                         return "[vectors]";
 #endif
                 return "[vdso]";
+        } else if (vma->vm_start == (vdso_text + (vdso_pages << PAGE_SHIFT))) {
+                return "[vvar]";
         }
 
         return NULL;