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Subject[PATCH 3/5] 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.

Cc: stable@vger.kernel.org # 3.9+
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/events/uprobes.c | 18 +++++++++++-------
1 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index c09d417..c836135 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;

+ 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;
+ 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() */
--
1.5.5.1


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