linux-kernel - [PATCH v1 6/9] uretprobes: Return probe exit, invoke handlers

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Date:	Wed,  3 Apr 2013 18:00:36 +0200
From:	Anton Arapov <anton@...hat.com>
To:	Anton Arapov <anton@...hat.com>, Oleg Nesterov <oleg@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Josh Stone <jistone@...hat.com>,
	Frank Eigler <fche@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	adrian.m.negreanu@...el.com, Torsten.Polle@....de
Subject: [PATCH v1 6/9] uretprobes: Return probe exit, invoke handlers

Uretprobe handlers are invoked when the trampoline is hit, on completion the
trampoline is replaced with the saved return address and the uretprobe instance
deleted.

v1 changes:
* pass bp_vaddr to ret_handler()
* simplify handle_uretprobe()

RFCv6 changes:
* rework handle_uretprobe()

RFCv5 changes:
* switch to simply linked list ->return_uprobes
* rework handle_uretprobe()

RFCv4 changes:
* check, whether utask is not NULL in handle_uretprobe()
* get rid of area->rp_trampoline_vaddr
* minor handle_uretprobe() fixups

RFCv3 changes:
* protected uprobe with refcounter. See put_uprobe() in handle_uretprobe()
  that reflects increment in prepare_uretprobe()

RFCv2 changes:
* get rid of ->return_consumers member from struct uprobe, introduce
  ret_handler() in consumer instead

Signed-off-by: Anton Arapov <anton@...hat.com>
---
 kernel/events/uprobes.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 59 insertions(+), 1 deletion(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 08ecfff..d129c1d 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1609,6 +1609,57 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
 	up_read(&uprobe->register_rwsem);
 }
 
+static void
+handler_uretprobe_chain(struct return_instance *ri, struct pt_regs *regs)
+{
+	struct uprobe *uprobe = ri->uprobe;
+	struct uprobe_consumer *uc;
+
+	down_read(&uprobe->register_rwsem);
+	for (uc = uprobe->consumers; uc; uc = uc->next) {
+		if (uc->ret_handler)
+			uc->ret_handler(uc, ri->func, regs);
+	}
+	up_read(&uprobe->register_rwsem);
+}
+
+static bool handler_uretprobe(struct pt_regs *regs)
+{
+	struct uprobe_task *utask;
+	struct return_instance *ri, *tmp;
+	bool chained;
+
+	utask = current->utask;
+	if (!utask)
+		return false;
+
+	ri = utask->return_instances;
+	if (!ri)
+		return false;
+
+	instruction_pointer_set(regs, ri->orig_ret_vaddr);
+
+	for (;;) {
+		handler_uretprobe_chain(ri, regs);
+
+		chained = ri->chained;
+		put_uprobe(ri->uprobe);
+
+		tmp = ri;
+		ri = ri->next;
+		kfree(tmp);
+
+		if (!chained)
+			break;
+
+		BUG_ON(!ri);
+	}
+
+	utask->return_instances = ri;
+
+	return true;
+}
+
 /*
  * Run handler and ask thread to singlestep.
  * Ensure all non-fatal signals cannot interrupt thread while it singlesteps.
@@ -1620,8 +1671,15 @@ static void handle_swbp(struct pt_regs *regs)
 	int uninitialized_var(is_swbp);
 
 	bp_vaddr = uprobe_get_swbp_addr(regs);
-	uprobe = find_active_uprobe(bp_vaddr, &is_swbp);
+	if (bp_vaddr == get_trampoline_vaddr()) {
+		if (handler_uretprobe(regs))
+			return;
 
+		pr_warn("uprobe: unable to handle uretprobe pid/tgid=%d/%d\n",
+						current->pid, current->tgid);
+	}
+
+	uprobe = find_active_uprobe(bp_vaddr, &is_swbp);
 	if (!uprobe) {
 		if (is_swbp > 0) {
 			/* No matching uprobe; signal SIGTRAP. */
-- 
1.8.1.4

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