Commit bc9bbb81 authored by Qi Zheng's avatar Qi Zheng Committed by Peter Zijlstra
Browse files

x86: Fix get_wchan() to support the ORC unwinder 



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: ee9f8fce ("x86/unwind: Add the ORC unwinder")
Signed-off-by: default avatarQi Zheng <zhengqi.arch@bytedance.com>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211008111626.271115116@infradead.org
parent 4e046156

arch/x86/kernel/process.c

+3 −48
Original line number Diff line number Diff line
@@ -944,58 +944,13 @@ unsigned long arch_randomize_brk(struct mm_struct *mm) 
 */

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 == current || task_is_running(p))

		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 && !task_is_running(p));



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,