From: Oleg Nesterov <oleg@xxxxxxxxxx> [ Upstream commit c7b4133c48445dde789ed30b19ccb0448c7593f7 ] 1. Clear utask->xol_vaddr unconditionally, even if this addr is not valid, xol_free_insn_slot() should never return with utask->xol_vaddr != NULL. 2. Add a comment to explain why do we need to validate slot_addr. 3. Simplify the validation above. We can simply check offset < PAGE_SIZE, unsigned underflows are fine, it should work if slot_addr < area->vaddr. 4. Kill the unnecessary "slot_nr >= UINSNS_PER_PAGE" check, slot_nr must be valid if offset < PAGE_SIZE. The next patches will cleanup this function even more. Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20240929144235.GA9471@xxxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- kernel/events/uprobes.c | 21 +++++++++------------ 1 file changed, 9 insertions(+), 12 deletions(-) diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 6dac0b5798213..5ce3d189e33c2 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -1629,8 +1629,8 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe) static void xol_free_insn_slot(struct task_struct *tsk) { struct xol_area *area; - unsigned long vma_end; unsigned long slot_addr; + unsigned long offset; if (!tsk->mm || !tsk->mm->uprobes_state.xol_area || !tsk->utask) return; @@ -1639,24 +1639,21 @@ static void xol_free_insn_slot(struct task_struct *tsk) if (unlikely(!slot_addr)) return; + tsk->utask->xol_vaddr = 0; area = tsk->mm->uprobes_state.xol_area; - vma_end = area->vaddr + PAGE_SIZE; - if (area->vaddr <= slot_addr && slot_addr < vma_end) { - unsigned long offset; - int slot_nr; - - offset = slot_addr - area->vaddr; - slot_nr = offset / UPROBE_XOL_SLOT_BYTES; - if (slot_nr >= UINSNS_PER_PAGE) - return; + offset = slot_addr - area->vaddr; + /* + * slot_addr must fit into [area->vaddr, area->vaddr + PAGE_SIZE). + * This check can only fail if the "[uprobes]" vma was mremap'ed. + */ + if (offset < PAGE_SIZE) { + int slot_nr = offset / UPROBE_XOL_SLOT_BYTES; clear_bit(slot_nr, area->bitmap); atomic_dec(&area->slot_count); smp_mb__after_atomic(); /* pairs with prepare_to_wait() */ if (waitqueue_active(&area->wq)) wake_up(&area->wq); - - tsk->utask->xol_vaddr = 0; } } -- 2.43.0
