From: Ryan Roberts <ryan.roberts@arm.com>
To: Dev Jain <dev.jain@arm.com>, catalin.marinas@arm.com, will@kernel.org
Cc: anshuman.khandual@arm.com, quic_zhenhuah@quicinc.com,
kevin.brodsky@arm.com, yangyicong@hisilicon.com,
joey.gouly@arm.com, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, mark.rutland@arm.com,
maz@kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] arm64/mm: Fix use-after-free due to race between memory hotunplug and ptdump
Date: Mon, 28 Jul 2025 12:13:51 +0100 [thread overview]
Message-ID: <f0e12d1e-110d-4a56-9f77-8fe2d664b0d1@arm.com> (raw)
In-Reply-To: <20250728103137.94726-1-dev.jain@arm.com>
On 28/07/2025 11:31, Dev Jain wrote:
> Memory hotunplug is done under the hotplug lock and ptdump walk is done
> under the init_mm.mmap_lock. Therefore, ptdump and hotunplug can run
> simultaneously without any synchronization. During hotunplug,
> free_empty_tables() is ultimately called to free up the pagetables.
> The following race can happen, where x denotes the level of the pagetable:
>
> CPU1 CPU2
> free_empty_pxd_table
> ptdump_walk_pgd()
> Get p(x+1)d table from pxd entry
> pxd_clear
> free_hotplug_pgtable_page(p(x+1)dp)
> Still using the p(x+1)d table
>
> which leads to a user-after-free.
I'm not sure I understand this. ptdump_show() protects against this with
get_online_mems()/put_online_mems(), doesn't it? There are 2 paths that call
ptdump_walk_pgd(). This protects one of them. The other is ptdump_check_wx(); I
thought you (or Anshuman?) had a patch in flight to fix that with
[get|put]_online_mems() too?
Sorry if my memory is failing me here...
next prev parent reply other threads:[~2025-07-28 11:16 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-28 10:31 [PATCH] arm64/mm: Fix use-after-free due to race between memory hotunplug and ptdump Dev Jain
2025-07-28 10:42 ` Dev Jain
2025-07-28 11:13 ` Ryan Roberts [this message]
2025-07-28 11:31 ` Dev Jain
2025-07-28 11:56 ` Ryan Roberts
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