[PATCH 3/9] uprobes: allow arch access to xol slot

[David Long]

From: Rabin Vincent <rabin at rab.in>

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 at rab.in>
Signed-off-by: David A. Long <dave.long at linaro.org>
---
 include/linux/uprobes.h |  1 +
 kernel/events/uprobes.c | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 7a7c035..f6287f0 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -134,6 +134,7 @@ 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 2f3a4cb..64471bd 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1238,6 +1238,11 @@ 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 - allocate a slot for xol.
  * Returns the allocated slot address or 0.
@@ -1246,6 +1251,7 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
 {
 	struct xol_area *area;
 	unsigned long xol_vaddr;
+	void *kaddr;
 
 	area = get_xol_area();
 	if (!area)
@@ -1256,7 +1262,9 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
 		return 0;
 
 	/* Initialize the slot */
-	copy_to_page(area->page, xol_vaddr, uprobe->arch.insn, MAX_UINSN_BYTES);
+	kaddr = kmap_atomic(area->page);
+	arch_uprobe_xol_copy(&uprobe->arch, kaddr + (xol_vaddr & ~PAGE_MASK));
+	kunmap_atomic(kaddr);
 	/*
 	 * We probably need flush_icache_user_range() but it needs vma.
 	 * This should work on supported architectures too.
-- 
1.8.1.2