[PATCH -tip v4 04/12] kprobes: Add kretprobe_find_ret_addr() for searching return address

Masami Hiramatsu
2021-03-22T06:40:30Z

Add kretprobe_find_ret_addr() for searching correct return address
from kretprobe instance list.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
Changes in v3:
- Remove generic stacktrace fixup. Instead, it should be solved in
each unwinder. This just provide the generic interface.
Changes in v2:
- Add is_kretprobe_trampoline() for checking address outside of
kretprobe_find_ret_addr()
- Remove unneeded addr from kretprobe_find_ret_addr()
- Rename fixup_kretprobe_tramp_addr() to fixup_kretprobe_trampoline()
---
include/linux/kprobes.h | 22 +++++++++++
kernel/kprobes.c | 90 +++++++++++++++++++++++++++++++++--------------
2 files changed, 86 insertions(+), 26 deletions(-)

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 65dadd4238a2..f530f82a046d 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -215,6 +215,14 @@ static nokprobe_inline void *kretprobe_trampoline_addr(void)
return dereference_function_descriptor(kretprobe_trampoline);
}

+static nokprobe_inline bool is_kretprobe_trampoline(unsigned long addr)
+{
+ return (void *)addr = kretprobe_trampoline_addr();
+}
+
+unsigned long kretprobe_find_ret_addr(struct task_struct *tsk, void *fp,
+ struct llist_node **cur);
+
/* If the trampoline handler called from a kprobe, use this version */
unsigned long __kretprobe_trampoline_handler(struct pt_regs *regs,
void *frame_pointer);
@@ -514,6 +522,20 @@ static inline bool is_kprobe_optinsn_slot(unsigned long addr)
}
#endif

+#if !defined(CONFIG_KRETPROBES)
+static nokprobe_inline bool is_kretprobe_trampoline(unsigned long addr)
+{
+ return false;
+}
+
+static nokprobe_inline
+unsigned long kretprobe_find_ret_addr(struct task_struct *tsk, void *fp,
+ struct llist_node **cur)
+{
+ return 0;
+}
+#endif
+
/* Returns true if kprobes handled the fault */
static nokprobe_inline bool kprobe_page_fault(struct pt_regs *regs,
unsigned int trap)
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 75c0a58c19c2..cf19edc038e4 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1858,45 +1858,68 @@ static struct notifier_block kprobe_exceptions_nb = {

#ifdef CONFIG_KRETPROBES

-unsigned long __kretprobe_trampoline_handler(struct pt_regs *regs,
- void *frame_pointer)
+/* This assumes the tsk is current or the task which is not running. */
+static unsigned long __kretprobe_find_ret_addr(struct task_struct *tsk,
+ struct llist_node **cur)
{
- kprobe_opcode_t *correct_ret_addr = NULL;
struct kretprobe_instance *ri = NULL;
- struct llist_node *first, *node;
- struct kretprobe *rp;
+ struct llist_node *node = *cur;
+
+ if (!node)
+ node = tsk->kretprobe_instances.first;
+ else
+ node = node->next;

- /* Find all nodes for this frame. */
- first = node = current->kretprobe_instances.first;
while (node) {
ri = container_of(node, struct kretprobe_instance, llist);
-
- BUG_ON(ri->fp != frame_pointer);
-
if (ri->ret_addr != kretprobe_trampoline_addr()) {
- correct_ret_addr = ri->ret_addr;
- /*
- * This is the real return address. Any other
- * instances associated with this task are for
- * other calls deeper on the call stack
- */
- goto found;
+ *cur = node;
+ return (unsigned long)ri->ret_addr;
}
-
node = node->next;
}
- pr_err("Oops! Kretprobe fails to find correct return address.\n");
- BUG_ON(1);
+ return 0;
+}
+NOKPROBE_SYMBOL(__kretprobe_find_ret_addr);

-found:
- /* Unlink all nodes for this frame. */
- current->kretprobe_instances.first = node->next;
- node->next = NULL;
+unsigned long kretprobe_find_ret_addr(struct task_struct *tsk, void *fp,
+ struct llist_node **cur)
+{
+ struct kretprobe_instance *ri = NULL;
+ unsigned long ret;
+
+ do {
+ ret = __kretprobe_find_ret_addr(tsk, cur);
+ if (!ret)
+ return ret;
+ ri = container_of(*cur, struct kretprobe_instance, llist);
+ } while (ri->fp != fp);
+
+ return ret;
+}
+NOKPROBE_SYMBOL(kretprobe_find_ret_addr);

- /* Run them.. */
+unsigned long __kretprobe_trampoline_handler(struct pt_regs *regs,
+ void *frame_pointer)
+{
+ kprobe_opcode_t *correct_ret_addr = NULL;
+ struct kretprobe_instance *ri = NULL;
+ struct llist_node *first, *node = NULL;
+ struct kretprobe *rp;
+
+ /* Find correct address and all nodes for this frame. */
+ correct_ret_addr = (void *)__kretprobe_find_ret_addr(current, &node);
+ if (!correct_ret_addr) {
+ pr_err("Oops! Kretprobe fails to find correct return address.\n");
+ BUG_ON(1);
+ }
+
+ /* Run them. */
+ first = current->kretprobe_instances.first;
while (first) {
ri = container_of(first, struct kretprobe_instance, llist);
- first = first->next;
+
+ BUG_ON(ri->fp != frame_pointer);

rp = get_kretprobe(ri);
if (rp && rp->handler) {
@@ -1907,6 +1930,21 @@ unsigned long __kretprobe_trampoline_handler(struct pt_regs *regs,
rp->handler(ri, regs);
__this_cpu_write(current_kprobe, prev);
}
+ if (first = node)
+ break;
+
+ first = first->next;
+ }
+
+ /* Unlink all nodes for this frame. */
+ first = current->kretprobe_instances.first;
+ current->kretprobe_instances.first = node->next;
+ node->next = NULL;
+
+ /* Recycle them. */
+ while (first) {
+ ri = container_of(first, struct kretprobe_instance, llist);
+ first = first->next;

recycle_rp_inst(ri);
}