From: Qi Zheng <zhengqi.arch@bytedance.com>
Date: Wed, 29 Sep 2021 15:02:17 -0700
Subject: x86: Fix get_wchan() to support the ORC unwinder
Git-commit: bc9bbb81730ea667c31c5b284f95ee312bab466f
Patch-mainline: v5.16-rc1
References: git-fixes

Currently, the kernel CONFIG_UNWINDER_ORC option is enabled by default
on x86, but the implementation of get_wchan() is still based on the frame
pointer unwinder, so the /proc/<pid>/wchan usually returned 0 regardless
of whether the task <pid> is running.

Reimplement get_wchan() by calling stack_trace_save_tsk(), which is
adapted to the ORC and frame pointer unwinders.

Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211008111626.271115116@infradead.org

Acked-by: Nikolay Borisov <nik.borisov@suse.com>
---
 arch/x86/kernel/process.c |   53 +++-------------------------------------------
 1 file changed, 4 insertions(+), 49 deletions(-)

--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -788,58 +788,13 @@ unsigned long arch_randomize_brk(struct
  */
 unsigned long get_wchan(struct task_struct *p)
 {
-	unsigned long start, bottom, top, sp, fp, ip, ret = 0;
-	int count = 0;
+	unsigned long entry = 0;
 
-	if (!p || p == current || p->state == TASK_RUNNING)
+	if (p == current || p->state == TASK_RUNNING)
 		return 0;
 
-	if (!try_get_task_stack(p))
-		return 0;
-
-	start = (unsigned long)task_stack_page(p);
-	if (!start)
-		goto out;
-
-	/*
-	 * Layout of the stack page:
-	 *
-	 * ----------- topmax = start + THREAD_SIZE - sizeof(unsigned long)
-	 * PADDING
-	 * ----------- top = topmax - TOP_OF_KERNEL_STACK_PADDING
-	 * stack
-	 * ----------- bottom = start
-	 *
-	 * The tasks stack pointer points at the location where the
-	 * framepointer is stored. The data on the stack is:
-	 * ... IP FP ... IP FP
-	 *
-	 * We need to read FP and IP, so we need to adjust the upper
-	 * bound by another unsigned long.
-	 */
-	top = start + THREAD_SIZE - TOP_OF_KERNEL_STACK_PADDING;
-	top -= 2 * sizeof(unsigned long);
-	bottom = start;
-
-	sp = READ_ONCE(p->thread.sp);
-	if (sp < bottom || sp > top)
-		goto out;
-
-	fp = READ_ONCE_NOCHECK(((struct inactive_task_frame *)sp)->bp);
-	do {
-		if (fp < bottom || fp > top)
-			goto out;
-		ip = READ_ONCE_NOCHECK(*(unsigned long *)(fp + sizeof(unsigned long)));
-		if (!in_sched_functions(ip)) {
-			ret = ip;
-			goto out;
-		}
-		fp = READ_ONCE_NOCHECK(*(unsigned long *)fp);
-	} while (count++ < 16 && p->state != TASK_RUNNING);
-
-out:
-	put_task_stack(p);
-	return ret;
+	stack_trace_save_tsk(p, &entry, 1, 0);
+	return entry;
 }
 
 long do_arch_prctl_common(struct task_struct *task, int option,