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>

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index ad17d81..7d12a45 100644 (file)
--- 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() */