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From:   Dexuan Cui <decui@microsoft.com>
To:     "Rafael J. Wysocki" <rafael@kernel.org>
CC:     Michael Kelley <mikelley@microsoft.com>,
        "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
        "rjw@rjwysocki.net" <rjw@rjwysocki.net>,
        "len.brown@intel.com" <len.brown@intel.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>
Subject: RE: [PATCH] ACPI: scan: Fix a Hyper-V Linux VM panic caused by buffer
 overflow
Thread-Topic: [PATCH] ACPI: scan: Fix a Hyper-V Linux VM panic caused by
 buffer overflow
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Date:   Fri, 8 Jan 2021 07:06:53 +0000
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> From: Rafael J. Wysocki <rafael@kernel.org>
> Sent: Thursday, January 7, 2021 5:48 AM
> > > > Linux VM on Hyper-V crashes with the latest mainline:
> > > > ...
> The root cause is a VM issue AFAICS, though.

Yes.
=20
> It doesn't look like the right fix to me, though.
>=20
> The problem appears to be that the string coming from _HID is too long
> (which is a spec violation).=20

Yes. We have requested Hyper-V team to fix the buggy BIOS/firmware,
but we have to cope with the existing buggy Hyper-V hosts, at least
before the Hyper-V fix is deployed to the hosts, and some old versions
of the hosts may not get updated. :-(

> The patch truncates it to match the
> length of the target buffer, but that is not particularly useful.
>=20
> It would be better to use something like kstrdup_const() to initialize
> acpi_device_bus_id->bus_id IMV.

Makes sense. I'll submit v2 shortly.

Thanks,
-- Dexuan