linux-kernel - Re: [PATCH v8 13/19] locking/rwsem: Make rwsem->owner an atomic_long

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Date:   Sat, 20 Jul 2019 13:10:13 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Luis Henriques <lhenriques@...e.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Waiman Long <longman@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Will Deacon <will.deacon@....com>,
        huang ying <huang.ying.caritas@...il.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Jeff Layton <jlayton@...nel.org>
Subject: Re: [PATCH v8 13/19] locking/rwsem: Make rwsem->owner an
 atomic_long_t

On Sat, Jul 20, 2019 at 09:41:05AM +0100, Luis Henriques wrote:
> [   39.801179] ==================================================================
> [   39.801973] BUG: KASAN: use-after-free in rwsem_down_write_slowpath (/home/miguel/kernel/linux/kernel/locking/rwsem.c:669 /home/miguel/kernel/linux/kernel/locking/rwsem.c:1125) 

That's rwsem_can_spin_on_owner(), specifically line 669 seems to suggest
owner_on_cpu().

So we'd somehow have a dead owner; I'm not immediately seeing how that
can happen.