| Date | Sat, 15 Oct 2011 21:01:48 +0200 | From | Oleg Nesterov <> | Subject | [PATCH 5/X] uprobes: xol_alloc_area() needs memory barriers |
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If xol_get_insn_slot() or xol_alloc_area() races with another thread doing xol_add_vma() it is not safe to dereference ->uprobes_xol_area.
Add the necessary wmb/read_barrier_depends pair, this ensures that xol_get_insn_slot() always sees the properly initialized memory.
Other users of ->uprobes_xol_area look fine, they can't race with xol_add_vma() this way. xol_free_insn_slot() checks utask->xol_vaddr, and free_uprobes_xol_area() is calles by mmput().
Except: valid_vma() is racy but it should not use ->uprobes_xol_area as we discussed. --- kernel/uprobes.c | 15 ++++++++++++--- 1 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/kernel/uprobes.c b/kernel/uprobes.c index 5c2554c..b59af3b 100644 --- a/kernel/uprobes.c +++ b/kernel/uprobes.c @@ -1087,6 +1087,7 @@ static int xol_add_vma(struct uprobes_xol_area *area) } area->vaddr = addr; + smp_wmb(); /* pairs with get_uprobes_xol_area() */ mm->uprobes_xol_area = area; ret = 0; fail: @@ -1094,6 +1095,14 @@ fail: return ret; } +static inline +struct uprobes_xol_area *get_uprobes_xol_area(struct mm_struct *mm) +{ + struct uprobes_xol_area *area = mm->uprobes_xol_area; + smp_read_barrier_depends(); /* pairs with wmb in xol_add_vma() */ + return area; +} + /* * xol_alloc_area - Allocate process's uprobes_xol_area. * This area will be used for storing instructions for execution out of @@ -1124,7 +1133,7 @@ static struct uprobes_xol_area *xol_alloc_area(void) fail: kfree(area->bitmap); kfree(area); - return current->mm->uprobes_xol_area; + return get_uprobes_xol_area(current->mm); } /* @@ -1183,17 +1192,17 @@ static unsigned long xol_take_insn_slot(struct uprobes_xol_area *area) static unsigned long xol_get_insn_slot(struct uprobe *uprobe, unsigned long slot_addr) { - struct uprobes_xol_area *area = current->mm->uprobes_xol_area; + struct uprobes_xol_area *area; unsigned long offset; void *vaddr; + area = get_uprobes_xol_area(current->mm); if (!area) { area = xol_alloc_area(); if (!area) return 0; } current->utask->xol_vaddr = xol_take_insn_slot(area); - /* * Initialize the slot if xol_vaddr points to valid * instruction slot. -- 1.5.5.1
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