[PATCH 4/9] uprobes: allow arch access to xol slot

[rabin@rab.in (Rabin Vincent)]

Allow arches to customize how the instruction is filled into the xol
slot.  ARM will use this to insert an undefined instruction after the
real instruction in order to simulate a single step of the instruction
without hardware support.

Signed-off-by: Rabin Vincent <rabin@rab.in>
---
 include/linux/uprobes.h |    1 +
 kernel/events/uprobes.c |    7 ++++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index da21b66..b4380ad 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -129,6 +129,7 @@ extern bool arch_uprobe_xol_was_trapped(struct task_struct *tsk);
 extern int  arch_uprobe_exception_notify(struct notifier_block *self, unsigned long val, void *data);
 extern void arch_uprobe_abort_xol(struct arch_uprobe *aup, struct pt_regs *regs);
 extern bool __weak arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *regs);
+extern void __weak arch_uprobe_xol_copy(struct arch_uprobe *auprobe, void *vaddr);
 #else /* !CONFIG_UPROBES */
 struct uprobes_state {
 };
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index a0e1a38..f7ff3a4 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1211,6 +1211,11 @@ static unsigned long xol_take_insn_slot(struct xol_area *area)
 	return slot_addr;
 }
 
+void __weak arch_uprobe_xol_copy(struct arch_uprobe *auprobe, void *vaddr)
+{
+	memcpy(vaddr, auprobe->insn, MAX_UINSN_BYTES);
+}
+
 /*
  * xol_get_insn_slot - If was not allocated a slot, then
  * allocate a slot.
@@ -1240,7 +1245,7 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe, unsigned long slot
 	current->utask->vaddr = slot_addr;
 	offset = current->utask->xol_vaddr & ~PAGE_MASK;
 	vaddr = kmap_atomic(area->page);
-	memcpy(vaddr + offset, uprobe->arch.insn, MAX_UINSN_BYTES);
+	arch_uprobe_xol_copy(&uprobe->arch, vaddr + offset);
 	kunmap_atomic(vaddr);
 
 	return current->utask->xol_vaddr;
-- 
1.7.9.5