Recover the return address on the stack which changed by the
kretprobe. Note that this does not recover the address on the
!current stack trace if CONFIG_ARCH_STACKWALK=n because old
stack trace interface doesn't lock the stack in the generic
stack_trace_save*() functions.
So with this patch, ftrace correctly shows the stacktrace
as below;
# echo r vfs_read > kprobe_events
# echo stacktrace > events/kprobes/r_vfs_read_0/trigger
# echo 1 > events/kprobes/r_vfs_read_0/enable
# echo 1 > options/sym-offset
# less trace
...
sh-132 [007] ...1 22.524917: <stack trace>
=> kretprobe_dispatcher+0x7d/0xc0
=> __kretprobe_trampoline_handler+0xdb/0x1b0
=> trampoline_handler+0x48/0x60
=> kretprobe_trampoline+0x2a/0x50
=> ksys_read+0x70/0xf0
=> __x64_sys_read+0x1a/0x20
=> do_syscall_64+0x38/0x50
=> entry_SYSCALL_64_after_hwframe+0x44/0xae
=> 0
The trampoline_handler+0x48 is actual call site address,
not modified by kretprobe.
Reported-by: Daniel Xu <dxu@xxxxxxxxx>
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
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 | 73 ++++++++++++++++++++++++++++++-----------------
kernel/stacktrace.c | 22 ++++++++++++++
3 files changed, 91 insertions(+), 26 deletions(-)
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 65dadd4238a2..674b5adad281 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,
+ 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,
+ 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..2550521ff64d 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1858,45 +1858,51 @@ 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. */
+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_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.. */
+ /* 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 +1913,21 @@ 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);
}
diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 9f8117c7cfdd..511287069473 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -13,6 +13,7 @@
#include <linux/export.h>
#include <linux/kallsyms.h>
#include <linux/stacktrace.h>
+#include <linux/kprobes.h>
/**
* stack_trace_print - Print the entries in the stack trace
@@ -69,6 +70,18 @@ int stack_trace_snprint(char *buf, size_t size, const unsigned long *entries,
}
EXPORT_SYMBOL_GPL(stack_trace_snprint);
+static void fixup_kretprobe_trampoline(unsigned long *store, unsigned int len,
+ struct task_struct *tsk)
+{
+ struct llist_node *cur = NULL;
+
+ while (len--) {
+ if (is_kretprobe_trampoline(*store))
+ *store = kretprobe_find_ret_addr(tsk, &cur);
+ store++;
+ }
+}
+
#ifdef CONFIG_ARCH_STACKWALK
struct stacktrace_cookie {
@@ -119,6 +132,7 @@ unsigned int stack_trace_save(unsigned long *store, unsigned int size,
};
arch_stack_walk(consume_entry, &c, current, NULL);
+ fixup_kretprobe_trampoline(store, c.len, current);
return c.len;
}
EXPORT_SYMBOL_GPL(stack_trace_save);
@@ -147,6 +161,7 @@ unsigned int stack_trace_save_tsk(struct task_struct *tsk, unsigned long *store,
return 0;
arch_stack_walk(consume_entry, &c, tsk, NULL);
+ fixup_kretprobe_trampoline(store, c.len, tsk);
put_task_stack(tsk);
return c.len;
}
@@ -171,6 +186,7 @@ unsigned int stack_trace_save_regs(struct pt_regs *regs, unsigned long *store,
};
arch_stack_walk(consume_entry, &c, current, regs);
+ fixup_kretprobe_trampoline(store, c.len, current);
return c.len;
}
@@ -205,6 +221,8 @@ int stack_trace_save_tsk_reliable(struct task_struct *tsk, unsigned long *store,
return 0;
ret = arch_stack_walk_reliable(consume_entry, &c, tsk);
+ if (!ret)
+ fixup_kretprobe_trampoline(store, c.len, tsk);
put_task_stack(tsk);
return ret ? ret : c.len;
}
@@ -276,6 +294,8 @@ unsigned int stack_trace_save(unsigned long *store, unsigned int size,
};
save_stack_trace(&trace);
+ fixup_kretprobe_trampoline(store, trace.nr_entries, current);
+
return trace.nr_entries;
}
EXPORT_SYMBOL_GPL(stack_trace_save);
@@ -323,6 +343,8 @@ unsigned int stack_trace_save_regs(struct pt_regs *regs, unsigned long *store,
};
save_stack_trace_regs(regs, &trace);
+ fixup_kretprobe_trampoline(store, trace.nr_entries, current);
+
return trace.nr_entries;
}
