linux-kernel - [PATCH 4.9 063/101] nios2: time: Read timer in get

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Date:   Tue, 23 Aug 2022 10:03:36 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Laura Abbott <labbott@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Daniel Micay <danielmicay@...il.com>,
        Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH 4.9 063/101] nios2: time: Read timer in get_cycles only if initialized

From: Guenter Roeck <linux@...ck-us.net>

commit 65d1e3ddeae117f6a224535e10a09145f0f96508 upstream.

Mainline crashes as follows when running nios2 images.

On node 0 totalpages: 65536
free_area_init_node: node 0, pgdat c8408fa0, node_mem_map c8726000
  Normal zone: 512 pages used for memmap
  Normal zone: 0 pages reserved
  Normal zone: 65536 pages, LIFO batch:15
Unable to handle kernel NULL pointer dereference at virtual address 00000000
ea = c8003cb0, ra = c81cbf40, cause = 15
Kernel panic - not syncing: Oops

Problem is seen because get_cycles() is called before the timer it depends
on is initialized. Returning 0 in that situation fixes the problem.

Fixes: 33d72f3822d7 ("init/main.c: extract early boot entropy from the ..")
Cc: Laura Abbott <labbott@...hat.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Daniel Micay <danielmicay@...il.com>
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/nios2/kernel/time.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/arch/nios2/kernel/time.c
+++ b/arch/nios2/kernel/time.c
@@ -107,7 +107,10 @@ static struct nios2_clocksource nios2_cs
 
 cycles_t get_cycles(void)
 {
-	return nios2_timer_read(&nios2_cs.cs);
+	/* Only read timer if it has been initialized */
+	if (nios2_cs.timer.base)
+		return nios2_timer_read(&nios2_cs.cs);
+	return 0;
 }
 EXPORT_SYMBOL(get_cycles);