linux-kernel - [PATCH 3.2 127/185] ARM: 7912/1: check stack pointer in get

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Message-ID: <lsq.1388282924.661315400@decadent.org.uk>
Date:	Sun, 29 Dec 2013 03:08:44 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Russell King" <rmk+kernel@....linux.org.uk>,
	"Will Deacon" <will.deacon@....com>,
	"Konstantin Khlebnikov" <k.khlebnikov@...sung.com>
Subject: [PATCH 3.2 127/185] ARM: 7912/1: check stack pointer in get_wchan

3.2.54-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Konstantin Khlebnikov <k.khlebnikov@...sung.com>

commit 1b15ec7a7427d4188ba91b9bbac696250a059d22 upstream.

get_wchan() is lockless. Task may wakeup at any time and change its own stack,
thus each next stack frame may be overwritten and filled with random stuff.

/proc/$pid/stack interface had been disabled for non-current tasks, see [1]
But 'wchan' still allows to trigger stack frame unwinding on volatile stack.

This patch fixes oops in unwind_frame() by adding stack pointer validation on
each step (as x86 code do), unwind_frame() already checks frame pointer.

Also I've found another report of this oops on stackoverflow (irony).

Link: http://www.spinics.net/lists/arm-kernel/msg110589.html [1]
Link: http://stackoverflow.com/questions/18479894/unwind-frame-cause-a-kernel-paging-error

Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@...sung.com>
Acked-by: Will Deacon <will.deacon@....com>
Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/arm/kernel/process.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -468,6 +468,7 @@ EXPORT_SYMBOL(kernel_thread);
 unsigned long get_wchan(struct task_struct *p)
 {
 	struct stackframe frame;
+	unsigned long stack_page;
 	int count = 0;
 	if (!p || p == current || p->state == TASK_RUNNING)
 		return 0;
@@ -476,9 +477,11 @@ unsigned long get_wchan(struct task_stru
 	frame.sp = thread_saved_sp(p);
 	frame.lr = 0;			/* recovered from the stack */
 	frame.pc = thread_saved_pc(p);
+	stack_page = (unsigned long)task_stack_page(p);
 	do {
-		int ret = unwind_frame(&frame);
-		if (ret < 0)
+		if (frame.sp < stack_page ||
+		    frame.sp >= stack_page + THREAD_SIZE ||
+		    unwind_frame(&frame) < 0)
 			return 0;
 		if (!in_sched_functions(frame.pc))
 			return frame.pc;

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