[PATCH v4 01/23] kprobes: Add generic kretprobe trampoline handler

Masami Hiramatsu
2020-08-28T12:27:20Z

Add a generic kretprobe trampoline handler for unifying
the all cloned /arch/* kretprobe trampoline handlers.

The generic kretprobe trampoline handler is based on the
x86 implementation, because it is the latest implementation.
It has frame pointer checking, kprobe_busy_begin/end and
return address fixup for user handlers.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
Changes in v4:
- Remove orig_ret_address
- Change the type of trampoline_address to void *
---
include/linux/kprobes.h | 32 ++++++++++++++--
kernel/kprobes.c | 96 +++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 124 insertions(+), 4 deletions(-)

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 9be1bff4f586..c6a913e608b7 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -187,10 +187,38 @@ static inline int kprobes_built_in(void)
return 1;
}

+extern struct kprobe kprobe_busy;
+void kprobe_busy_begin(void);
+void kprobe_busy_end(void);
+
#ifdef CONFIG_KRETPROBES
extern void arch_prepare_kretprobe(struct kretprobe_instance *ri,
struct pt_regs *regs);
extern int arch_trampoline_kprobe(struct kprobe *p);
+
+/* If the trampoline handler called from a kprobe, use this version */
+unsigned long __kretprobe_trampoline_handler(struct pt_regs *regs,
+ void *trampoline_address,
+ void *frame_pointer);
+
+static nokprobe_inline
+unsigned long kretprobe_trampoline_handler(struct pt_regs *regs,
+ void *trampoline_address,
+ void *frame_pointer)
+{
+ unsigned long ret;
+ /*
+ * Set a dummy kprobe for avoiding kretprobe recursion.
+ * Since kretprobe never runs in kprobe handler, any kprobe must not
+ * be running at this point.
+ */
+ kprobe_busy_begin();
+ ret = __kretprobe_trampoline_handler(regs, trampoline_address, frame_pointer);
+ kprobe_busy_end();
+
+ return ret;
+}
+
#else /* CONFIG_KRETPROBES */
static inline void arch_prepare_kretprobe(struct kretprobe *rp,
struct pt_regs *regs)
@@ -354,10 +382,6 @@ static inline struct kprobe_ctlblk *get_kprobe_ctlblk(void)
return this_cpu_ptr(&kprobe_ctlblk);
}

-extern struct kprobe kprobe_busy;
-void kprobe_busy_begin(void);
-void kprobe_busy_end(void);
-
kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset);
int register_kprobe(struct kprobe *p);
void unregister_kprobe(struct kprobe *p);
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 287b263c9cb9..46510e5000ff 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1927,6 +1927,102 @@ unsigned long __weak arch_deref_entry_point(void *entry)
}

#ifdef CONFIG_KRETPROBES
+
+unsigned long __kretprobe_trampoline_handler(struct pt_regs *regs,
+ void *trampoline_address,
+ void *frame_pointer)
+{
+ struct kretprobe_instance *ri = NULL, *last = NULL;
+ struct hlist_head *head, empty_rp;
+ struct hlist_node *tmp;
+ unsigned long flags;
+ kprobe_opcode_t *correct_ret_addr = NULL;
+ bool skipped = false;
+
+ INIT_HLIST_HEAD(&empty_rp);
+ kretprobe_hash_lock(current, &head, &flags);
+
+ /*
+ * It is possible to have multiple instances associated with a given
+ * task either because multiple functions in the call path have
+ * return probes installed on them, and/or more than one
+ * return probe was registered for a target function.
+ *
+ * We can handle this because:
+ * - instances are always pushed into the head of the list
+ * - when multiple return probes are registered for the same
+ * function, the (chronologically) first instance's ret_addr
+ * will be the real return address, and all the rest will
+ * point to kretprobe_trampoline.
+ */
+ hlist_for_each_entry(ri, head, hlist) {
+ if (ri->task != current)
+ /* another task is sharing our hash bucket */
+ continue;
+ /*
+ * Return probes must be pushed on this hash list correct
+ * order (same as return order) so that it can be popped
+ * correctly. However, if we find it is pushed it incorrect
+ * order, this means we find a function which should not be
+ * probed, because the wrong order entry is pushed on the
+ * path of processing other kretprobe itself.
+ */
+ if (ri->fp != frame_pointer) {
+ if (!skipped)
+ pr_warn("kretprobe is stacked incorrectly. Trying to fixup.\n");
+ skipped = true;
+ continue;
+ }
+
+ correct_ret_addr = ri->ret_addr;
+ if (skipped)
+ pr_warn("%ps must be blacklisted because of incorrect kretprobe order\n",
+ ri->rp->kp.addr);
+
+ if (correct_ret_addr != trampoline_address)
+ /*
+ * This is the real return address. Any other
+ * instances associated with this task are for
+ * other calls deeper on the call stack
+ */
+ break;
+ }
+
+ kretprobe_assert(ri, (unsigned long)correct_ret_addr,
+ (unsigned long)trampoline_address);
+ last = ri;
+
+ hlist_for_each_entry_safe(ri, tmp, head, hlist) {
+ if (ri->task != current)
+ /* another task is sharing our hash bucket */
+ continue;
+ if (ri->fp != frame_pointer)
+ continue;
+
+ if (ri->rp && ri->rp->handler) {
+ __this_cpu_write(current_kprobe, &ri->rp->kp);
+ ri->ret_addr = correct_ret_addr;
+ ri->rp->handler(ri, regs);
+ __this_cpu_write(current_kprobe, &kprobe_busy);
+ }
+
+ recycle_rp_inst(ri, &empty_rp);
+
+ if (ri == last)
+ break;
+ }
+
+ kretprobe_hash_unlock(current, &flags);
+
+ hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
+ hlist_del(&ri->hlist);
+ kfree(ri);
+ }
+
+ return (unsigned long)correct_ret_addr;
+}
+NOKPROBE_SYMBOL(__kretprobe_trampoline_handler)
+
/*
* This kprobe pre_handler is registered with every kretprobe. When probe
* hits it will set up the return probe.