[PATCH] kmemleak: clear stale pointers from task stacks

From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>
Cc: Andy Lutomirski <luto@kernel.org>
Subject: [PATCH] kmemleak: clear stale pointers from task stacks
Date: Fri, 06 Oct 2017 14:38:21 +0300	[thread overview]
Message-ID: <150728990124.744199.8403409836394318684.stgit@buzz> (raw)

Kmemleak considers any pointers as task stacks as references.
This patch clears newly allocated and reused vmap stacks.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
 include/linux/thread_info.h |    2 +-
 kernel/fork.c               |    4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index 905d769d8ddc..5f7eeab990fe 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -42,7 +42,7 @@ enum {
 #define THREAD_ALIGN	THREAD_SIZE
 #endif
 
-#ifdef CONFIG_DEBUG_STACK_USAGE
+#if IS_ENABLED(CONFIG_DEBUG_STACK_USAGE) || IS_ENABLED(CONFIG_DEBUG_KMEMLEAK)
 # define THREADINFO_GFP		(GFP_KERNEL_ACCOUNT | __GFP_NOTRACK | \
 				 __GFP_ZERO)
 #else
diff --git a/kernel/fork.c b/kernel/fork.c
index c4ff0303b7c5..53e3b6f8a3bf 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -213,6 +213,10 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
 		if (!s)
 			continue;
 
+#ifdef CONFIG_DEBUG_KMEMLEAK
+		/* Clear stale pointers from reused stack. */
+		memset(s->addr, 0, THREAD_SIZE);
+#endif
 		tsk->stack_vm_area = s;
 		return s->addr;
 	}

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