linux-kernel - Re: [PATCH v2] kasan: remove kasan_find_vm

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Message-ID:
 <GV1PR08MB1052126BB553BD36DA768C998FB4AA@GV1PR08MB10521.eurprd08.prod.outlook.com>
Date: Sat, 12 Jul 2025 15:46:10 +0000
From: Yeo Reum Yun <YeoReum.Yun@....com>
To: Byungchul Park <byungchul@...com>, Andrey Konovalov <andreyknvl@...il.com>
CC: "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"glider@...gle.com" <glider@...gle.com>, "dvyukov@...gle.com"
	<dvyukov@...gle.com>, Vincenzo Frascino <Vincenzo.Frascino@....com>,
	"bigeasy@...utronix.de" <bigeasy@...utronix.de>, "clrkwllms@...nel.org"
	<clrkwllms@...nel.org>, "rostedt@...dmis.org" <rostedt@...dmis.org>,
	"max.byungchul.park@...il.com" <max.byungchul.park@...il.com>,
	"ysk@...lloc.com" <ysk@...lloc.com>, "kasan-dev@...glegroups.com"
	<kasan-dev@...glegroups.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-rt-devel@...ts.linux.dev" <linux-rt-devel@...ts.linux.dev>,
	"kernel_team@...ynix.com" <kernel_team@...ynix.com>, "urezki@...il.com"
	<urezki@...il.com>
Subject: Re: [PATCH v2] kasan: remove kasan_find_vm_area() to prevent possible
 deadlock

Hi ByungChul,

[...]
> I checked the critical section by &vn->busy.lock in find_vm_area().  The
> time complextity looks O(log N).  I don't think an irq disabled section
> of O(log N) is harmful.  I still think using
> spin_lock_irqsave(&vn->busy.lock) can resolve this issue with no worry
> of significant irq delay.  Am I missing something?

I don't agree for this. 
since in PREEMPT_RT case, it has the same problem.

In case of PREEMPT_RT, spin_lock_irqsave() becomes rt_spin_lock() which is sleepable.
But, KASAN calls "rt_spin_lock()" holding raw_spin_lock_irqsave() which is definitely wrong.

But as Uladzislau said, without reference count manage, UAF can always happen.
IOW, If KASAN to dump vm information, I think we need:
    1. manage reference for vmap_area.
    2. find_vm_area() with rcu version.


Thanks.

--  
Sincerely,
Yeoreum Yun