x86, vdso: Move the vvar area before the vdso text

Putting the vvar area after the vdso text is rather complicated: it
only works of the total length of the vdso text mapping is known at
vdso link time, and the linker doesn't allow symbol addresses to
depend on the sizes of non-allocatable data after the PT_LOAD
segment.

Moving the vvar area before the vdso text will allow is to safely
map non-allocatable data after the vdso text, which is a nice
simplification.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/156c78c0d93144ff1055a66493783b9e56813983.1405040914.git.luto@amacapital.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 11 insertions, 9 deletions

diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c
index 5a5176de8d0a..dbef622bb5af 100644
--- a/arch/x86/vdso/vma.c
+++ b/arch/x86/vdso/vma.c
@@ -93,7 +93,7 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
 {
         struct mm_struct *mm = current->mm;
         struct vm_area_struct *vma;
-        unsigned long addr;
+        unsigned long addr, text_start;
         int ret = 0;
         static struct page *no_pages[] = {NULL};
         static struct vm_special_mapping vvar_mapping = {
@@ -103,26 +103,28 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
 
         if (calculate_addr) {
                 addr = vdso_addr(current->mm->start_stack,
-                                 image->sym_end_mapping);
+                                 image->size - image->sym_vvar_start);
         } else {
                 addr = 0;
         }
 
         down_write(&mm->mmap_sem);
 
-        addr = get_unmapped_area(NULL, addr, image->sym_end_mapping, 0, 0);
+        addr = get_unmapped_area(NULL, addr,
+                                 image->size - image->sym_vvar_start, 0, 0);
         if (IS_ERR_VALUE(addr)) {
                 ret = addr;
                 goto up_fail;
         }
 
-        current->mm->context.vdso = (void __user *)addr;
+        text_start = addr - image->sym_vvar_start;
+        current->mm->context.vdso = (void __user *)text_start;
 
         /*
          * MAYWRITE to allow gdb to COW and set breakpoints
          */
         vma = _install_special_mapping(mm,
-                                       addr,
+                                       text_start,
                                        image->size,
                                        VM_READ|VM_EXEC|
                                        VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
@@ -134,8 +136,8 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
         }
 
         vma = _install_special_mapping(mm,
-                                       addr + image->size,
-                                       image->sym_end_mapping - image->size,
+                                       addr,
+                                       -image->sym_vvar_start,
                                        VM_READ,
                                        &vvar_mapping);
 
@@ -146,7 +148,7 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
 
         if (image->sym_vvar_page)
                 ret = remap_pfn_range(vma,
-                                      addr + image->sym_vvar_page,
+                                      text_start + image->sym_vvar_page,
                                       __pa_symbol(&__vvar_page) >> PAGE_SHIFT,
                                       PAGE_SIZE,
                                       PAGE_READONLY);
@@ -157,7 +159,7 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
 #ifdef CONFIG_HPET_TIMER
         if (hpet_address && image->sym_hpet_page) {
                 ret = io_remap_pfn_range(vma,
-                        addr + image->sym_hpet_page,
+                        text_start + image->sym_hpet_page,
                         hpet_address >> PAGE_SHIFT,
                         PAGE_SIZE,
                         pgprot_noncached(PAGE_READONLY));