When a uprobe with return probe consumer is hit, prepare_uretprobe()
function is invoked. It creates return_instance, hijacks return address
and replaces it with the trampoline.
* Return instances are kept as stack per uprobed task.
* Return instance is chained, when the original return address is
trampoline's page vaddr (e.g. recursive call of the probed function).
v1 changes:
* preserve address of the breakpoint in return_instance.
* don't forget NULLify return_instances on free_utask.
* simplify prepare_uretprobe().
RFCv6 changes:
* rework prepare_uretprobe() logic in order to make further unwinding
in handler_uretprobe() simplier.
* introduce the 'dirty' field.
RFCv5 changes:
* switch from hlist to simply linked list for tracking ->*return_uprobes.
* preallocate first slot xol_area for return probes, see xol_get_area()
changes.
* add get_trampoline_vaddr() helper, to emphasize area->vaddr overload.
RFCv4 changes:
* get rid of area->rp_trampoline_vaddr as it always the same as ->vaddr.
* cleanup ->return_uprobes list in uprobe_free_utask(), because the
task can exit from inside the ret-probe'd function(s).
* in find_active_uprobe(): Once we inserted "int3" we must ensure that
handle_swbp() will be called even if this uprobe goes away. We have
the reference but it only protects uprobe itself, it can't protect
agains delete_uprobe().
IOW, we must ensure that uprobe_pre_sstep_notifier() can't return 0.
RFCv3 changes:
* protected uprobe with refcounter. See atomic_inc in prepare_uretprobe()
and put_uprobe() in a following patch in handle_uretprobe().
RFCv2 changes:
* get rid of ->return_consumers member from struct uprobe, introduce
ret_handler() in consumer.
Signed-off-by: Anton Arapov <an...@redhat.com>
---
include/linux/uprobes.h | 1 +
kernel/events/uprobes.c | 92 ++++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 92 insertions(+), 1 deletion(-)
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 4042cad..5f8960e 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -71,6 +71,7 @@ struct uprobe_task {
enum uprobe_task_state state;
struct arch_uprobe_task autask;
+ struct return_instance *return_instances;
struct uprobe *active_uprobe;
unsigned long xol_vaddr;
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index d3c8201..08ecfff 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -75,6 +75,15 @@ struct uprobe {
struct arch_uprobe arch;
};
+struct return_instance {
+ struct uprobe *uprobe;
+ unsigned long func;
+ unsigned long orig_ret_vaddr; /* original return address */
+ bool chained; /* true, if instance is nested
*/
+
+ struct return_instance *next; /* keep as stack */
+};
+
/*
* valid_vma: Verify if the specified vma is an executable vma
* Relax restrictions while unregistering: vm_flags might have
@@ -1294,6 +1303,7 @@ unsigned long __weak uprobe_get_swbp_addr(struct pt_regs
*regs)
void uprobe_free_utask(struct task_struct *t)
{
struct uprobe_task *utask = t->utask;
+ struct return_instance *ri, *tmp;
if (!utask)
return;
@@ -1301,6 +1311,15 @@ void uprobe_free_utask(struct task_struct *t)
if (utask->active_uprobe)
put_uprobe(utask->active_uprobe);
+ ri = utask->return_instances;
+ while (ri) {
+ tmp = ri;
+ ri = ri->next;
+
+ put_uprobe(tmp->uprobe);
+ kfree(tmp);
+ }
+
xol_free_insn_slot(t);
kfree(utask);
t->utask = NULL;
@@ -1348,6 +1367,65 @@ static unsigned long get_trampoline_vaddr(void)
return trampoline_vaddr;
}
+static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
+{
+ struct return_instance *ri;
+ struct uprobe_task *utask;
+ unsigned long orig_ret_vaddr, trampoline_vaddr;
+ bool chained = false;
+
+ if (!get_xol_area())
+ return;
+
+ utask = get_utask();
+ if (!utask)
+ return;
+
+ ri = kzalloc(sizeof(struct return_instance), GFP_KERNEL);
+ if (!ri)
+ goto fail;
+
+ trampoline_vaddr = get_trampoline_vaddr();
+ orig_ret_vaddr = arch_uretprobe_hijack_return_addr(trampoline_vaddr,
regs);
+ if (orig_ret_vaddr == -1)
+ goto fail;
+
+ /*
+ * We don't want to keep trampoline address in stack, rather keep the
+ * original return address of first caller thru all the consequent
+ * instances. This also makes breakpoint unwrapping easier.
+ */
+ if (orig_ret_vaddr == trampoline_vaddr) {
+ if (!utask->return_instances) {
+ /*
+ * This situation is not possible. Likely we have an
+ * attack from user-space.
+ */
+ pr_warn("uprobe: unable to set uretprobe
pid/tgid=%d/%d\n",
+ current->pid, current->tgid);
+ goto fail;
+ }
+
+ chained = true;
+ orig_ret_vaddr = utask->return_instances->orig_ret_vaddr;
+ }
+
+ atomic_inc(&uprobe->ref);
+ ri->uprobe = uprobe;
+ ri->func = instruction_pointer(regs);
+ ri->orig_ret_vaddr = orig_ret_vaddr;
+ ri->chained = chained;
+
+ /* add instance to the stack */
+ ri->next = utask->return_instances;
+ utask->return_instances = ri;
+
+ return;
+
+ fail:
+ kfree(ri);
+}
+
/* Prepare to single-step probed instruction out of line. */
static int
pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
@@ -1503,6 +1581,7 @@ static void handler_chain(struct uprobe *uprobe, struct
pt_regs *regs)
{
struct uprobe_consumer *uc;
int remove = UPROBE_HANDLER_REMOVE;
+ bool need_prep = false; /* prepare return uprobe, when needed */
down_read(&uprobe->register_rwsem);
for (uc = uprobe->consumers; uc; uc = uc->next) {
@@ -1513,9 +1592,16 @@ static void handler_chain(struct uprobe *uprobe, struct
pt_regs *regs)
WARN(rc & ~UPROBE_HANDLER_MASK,
"bad rc=0x%x from %pf()\n", rc, uc->handler);
}
+
+ if (uc->ret_handler)
+ need_prep = true;
+
remove &= rc;
}
+ if (need_prep && !remove)
+ prepare_uretprobe(uprobe, regs); /* put bp at return */
+
if (remove && uprobe->consumers) {
WARN_ON(!uprobe_is_active(uprobe));
unapply_uprobe(uprobe, current->mm);
@@ -1634,7 +1720,11 @@ void uprobe_notify_resume(struct pt_regs *regs)
*/
int uprobe_pre_sstep_notifier(struct pt_regs *regs)
{
- if (!current->mm || !test_bit(MMF_HAS_UPROBES, ¤t->mm->flags))
+ if (!current->mm)
+ return 0;
+
+ if (!test_bit(MMF_HAS_UPROBES, ¤t->mm->flags) &&
+ (!current->utask || !current->utask->return_instances))
return 0;
set_thread_flag(TIF_UPROBE);
--
1.8.1.4
--
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