uprobes: Teach __create_xol_area() to accept the predefined vaddr

Currently xol_add_vma() uses get_unmapped_area() for area->vaddr,
but the next patches need to use the fixed address. So this patch
adds the new "vaddr" argument to __create_xol_area() which should
be used as area->vaddr if it is nonzero.

xol_add_vma() doesn't bother to verify that the predefined addr is
not used, insert_vm_struct() should fail if find_vma_links() detects
the overlap with the existing vma.

Also, __create_xol_area() doesn't need __GFP_ZERO to allocate area.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

1 files changed, 12 insertions, 8 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index ad17d813e73e..7d12a45842a7 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1104,11 +1104,14 @@ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
         if (mm->uprobes_state.xol_area)
                 goto fail;
 
-        /* Try to map as high as possible, this is only a hint. */
-        area->vaddr = get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE, PAGE_SIZE, 0, 0);
-        if (area->vaddr & ~PAGE_MASK) {
-                ret = area->vaddr;
-                goto fail;
+        if (!area->vaddr) {
+                /* Try to map as high as possible, this is only a hint. */
+                area->vaddr = get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE,
+                                                PAGE_SIZE, 0, 0);
+                if (area->vaddr & ~PAGE_MASK) {
+                        ret = area->vaddr;
+                        goto fail;
+                }
         }
 
         ret = install_special_mapping(mm, area->vaddr, PAGE_SIZE,
@@ -1124,13 +1127,13 @@ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
         return ret;
 }
 
-static struct xol_area *__create_xol_area(void)
+static struct xol_area *__create_xol_area(unsigned long vaddr)
 {
         struct mm_struct *mm = current->mm;
         uprobe_opcode_t insn = UPROBE_SWBP_INSN;
         struct xol_area *area;
 
-        area = kzalloc(sizeof(*area), GFP_KERNEL);
+        area = kmalloc(sizeof(*area), GFP_KERNEL);
         if (unlikely(!area))
                 goto out;
 
@@ -1142,6 +1145,7 @@ static struct xol_area *__create_xol_area(void)
         if (!area->page)
                 goto free_bitmap;
 
+        area->vaddr = vaddr;
         init_waitqueue_head(&area->wq);
         /* Reserve the 1st slot for get_trampoline_vaddr() */
         set_bit(0, area->bitmap);
@@ -1172,7 +1176,7 @@ static struct xol_area *get_xol_area(void)
         struct xol_area *area;
 
         if (!mm->uprobes_state.xol_area)
-                __create_xol_area();
+                __create_xol_area(0);
 
         area = mm->uprobes_state.xol_area;
         smp_read_barrier_depends();     /* pairs with wmb in xol_add_vma() */