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From: Andy Lutomirski <luto@kernel.org>
To: x86@kernel.org
Cc: Borislav Petkov <bp@alien8.de>,
	linux-kernel@vger.kernel.org, Brian Gerst <brgerst@gmail.com>,
	Jann Horn <jann@thejh.net>, Josh Poimboeuf <jpoimboe@redhat.com>,
	Andy Lutomirski <luto@kernel.org>
Subject: [PATCH v2 5/8] x86/process: Pin the target stack in get_wchan()
Date: Thu, 15 Sep 2016 22:45:46 -0700
Message-ID: <337aeca8614024aa4d8d9c81053bbf8fcffbe4ad.1474003868.git.luto@kernel.org> (raw)
In-Reply-To: <cover.1474003868.git.luto@kernel.org>
In-Reply-To: <cover.1474003868.git.luto@kernel.org>

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

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/kernel/process.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 0b9ed8ec5226..4002b475171c 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -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;
 }
-- 
2.7.4

  parent reply index

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-16  5:45 [PATCH v2 0/8] thread_info cleanups and stack caching Andy Lutomirski
2016-09-16  5:45 ` [PATCH v2 1/8] x86/entry/64: Fix a minor comment rebase error Andy Lutomirski
2016-09-16  9:16   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-09-16  5:45 ` [PATCH v2 2/8] sched: Add try_get_task_stack() and put_task_stack() Andy Lutomirski
2016-09-16  9:16   ` [tip:x86/asm] sched/core: " tip-bot for Andy Lutomirski
2016-09-16  5:45 ` [PATCH v2 3/8] kthread: to_live_kthread() needs try_get_task_stack() Andy Lutomirski
2016-09-16  9:17   ` [tip:x86/asm] kthread: Pin the stack via try_get_task_stack()/put_task_stack() in to_live_kthread() function tip-bot for Oleg Nesterov
2016-09-16  5:45 ` [PATCH v2 4/8] x86/dumpstack: Pin the target stack when dumping it Andy Lutomirski
2016-09-16  9:17   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-09-16 11:55     ` Josh Poimboeuf
2016-09-16 12:28       ` Josh Poimboeuf
2016-09-16 12:57         ` Ingo Molnar
2016-09-16 13:05           ` [PATCH] x86/dumpstack: remove NULL task pointer convention Josh Poimboeuf
2016-09-16  5:45 ` Andy Lutomirski [this message]
2016-09-16  9:18   ` [tip:x86/asm] x86/process: Pin the target stack in get_wchan() tip-bot for Andy Lutomirski
2016-09-16  5:45 ` [PATCH v2 6/8] lib/syscall: Pin the task stack in collect_syscall() Andy Lutomirski
2016-09-16  9:18   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-09-16  5:45 ` [PATCH v2 7/8] sched: Free the stack early if CONFIG_THREAD_INFO_IN_TASK Andy Lutomirski
2016-09-16  9:19   ` [tip:x86/asm] sched/core: " tip-bot for Andy Lutomirski
2016-09-16  5:45 ` [PATCH v2 8/8] fork: Cache two thread stacks per cpu if CONFIG_VMAP_STACK is set Andy Lutomirski
2016-09-16  9:19   ` [tip:x86/asm] fork: Optimize task creation by caching two thread stacks per CPU if CONFIG_VMAP_STACK=y tip-bot for Andy Lutomirski

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