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Commit 74327a3e authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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x86/process: Pin the target stack in get_wchan() 



This will prevent a crash if get_wchan() runs after the task stack
is freed.

Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jann Horn <jann@thejh.net>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/337aeca8614024aa4d8d9c81053bbf8fcffbe4ad.1474003868.git.luto@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 1959a601

arch/x86/kernel/process.c

+15 −7
Original line number Diff line number Diff line
@@ -532,15 +532,18 @@ unsigned long thread_saved_pc(struct task_struct *tsk) 
 */

unsigned long get_wchan(struct task_struct *p)

{

	unsigned long start, bottom, top, sp, fp, ip;

	unsigned long start, bottom, top, sp, fp, ip, ret = 0;

	int count = 0;



	if (!p || 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)

		return 0;

		goto out;



	/*

	 * Layout of the stack page:
@@ -564,16 +567,21 @@ unsigned long get_wchan(struct task_struct *p) 


	sp = READ_ONCE(p->thread.sp);

	if (sp < bottom || sp > top)

		return 0;

		goto out;



	fp = READ_ONCE_NOCHECK(((struct inactive_task_frame *)sp)->bp);

	do {

		if (fp < bottom || fp > top)

			return 0;

			goto out;

		ip = READ_ONCE_NOCHECK(*(unsigned long *)(fp + sizeof(unsigned long)));

		if (!in_sched_functions(ip))

			return ip;

		if (!in_sched_functions(ip)) {

			ret = ip;

			goto out;

		}

		fp = READ_ONCE_NOCHECK(*(unsigned long *)fp);

	} while (count++ < 16 && p->state != TASK_RUNNING);

	return 0;



out:

	put_task_stack(p);

	return ret;

}