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Date:   Wed, 6 May 2020 01:53:31 -0400
From:   Qian Cai <cai@....pw>
To:     Walter Wu <walter-zh.wu@...iatek.com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        wsd_upstream <wsd_upstream@...iatek.com>,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 0/3] kasan: memorize and print call_rcu stack



> On May 6, 2020, at 1:19 AM, Walter Wu <walter-zh.wu@...iatek.com> wrote:
> 
> This patchset improves KASAN reports by making them to have
> call_rcu() call stack information. It is helpful for programmers
> to solve use-after-free or double-free memory issue.
> 
> The KASAN report was as follows(cleaned up slightly):
> 
> BUG: KASAN: use-after-free in kasan_rcu_reclaim+0x58/0x60
> 
> Freed by task 0:
> save_stack+0x24/0x50
> __kasan_slab_free+0x110/0x178
> kasan_slab_free+0x10/0x18
> kfree+0x98/0x270
> kasan_rcu_reclaim+0x1c/0x60
> rcu_core+0x8b4/0x10f8
> rcu_core_si+0xc/0x18
> efi_header_end+0x238/0xa6c
> 
> First call_rcu() call stack:
> save_stack+0x24/0x50
> kasan_record_callrcu+0xc8/0xd8
> call_rcu+0x190/0x580
> kasan_rcu_uaf+0x1d8/0x278
> 
> Last call_rcu() call stack:
> (stack is not available)
> 
> 
> Add new CONFIG option to record first and last call_rcu() call stack
> and KASAN report prints two call_rcu() call stack.
> 
> This option doesn't increase the cost of memory consumption. It is
> only suitable for generic KASAN.

I don’t understand why this needs to be a Kconfig option at all. If call_rcu() stacks are useful in general, then just always gather those information. How do developers judge if they need to select this option or not?

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