linux-hardening - [PATCH v2 5/6] x86: Fix get_wchan() to support the ORC unwinder

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Date:   Wed, 29 Sep 2021 15:02:17 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        kernel test robot <oliver.sang@...el.com>,
        Vito Caputo <vcaputo@...garu.com>,
        Jann Horn <jannh@...gle.com>, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Anand K Mistry <amistry@...gle.com>,
        "Kenta.Tada@...y.com" <Kenta.Tada@...y.com>,
        Alexey Gladkov <legion@...nel.org>,
        Michael Weiß <michael.weiss@...ec.fraunhofer.de>,
        Michal Hocko <mhocko@...e.com>, Helge Deller <deller@....de>,
        "Tobin C. Harding" <me@...in.cc>,
        Tycho Andersen <tycho@...ho.pizza>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Mark Rutland <mark.rutland@....com>,
        Jens Axboe <axboe@...nel.dk>,
        Stefan Metzmacher <metze@...ba.org>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Ohhoon Kwon <ohoono.kwon@...sung.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        YiFei Zhu <yifeifz2@...inois.edu>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-hardening@...r.kernel.org, x86@...nel.org
Subject: [PATCH v2 5/6] x86: Fix get_wchan() to support the ORC unwinder

From: Qi Zheng <zhengqi.arch@...edance.com>

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@...edance.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
Link: https://lore.kernel.org/r/20210831083625.59554-1-zhengqi.arch@bytedance.com
---
 arch/x86/kernel/process.c | 51 +++------------------------------------
 1 file changed, 3 insertions(+), 48 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 1d9463e3096b..e645925f9f02 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -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,
-- 
2.30.2