Date:   Fri, 24 Feb 2017 17:50:37 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Seunghun Han <kkamagui@...il.com>
Cc:     "Zheng, Lv" <lv.zheng@...el.com>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "devel@...ica.org" <devel@...ica.org>,
        Robert Moore <robert.moore@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] acpi: acpica: fix acpi operand cache leak

On Friday, February 24, 2017 09:56:21 PM Seunghun Han wrote:
> Hi, Rafeal.
> 
> I added my opinion below.
> 
> 2017-02-24 21:13 GMT+09:00 Rafael J. Wysocki <rjw@...ysocki.net>:
> > On Friday, February 24, 2017 09:15:52 PM Seunghun Han wrote:
> >> Hi, Rafael.
> >>
> >> I added my opinion below.
> >>
> >> 2017-02-24 20:50 GMT+09:00 Rafael J. Wysocki <rjw@...ysocki.net>:
> >> > On Friday, February 24, 2017 08:52:42 PM Seunghun Han wrote:
> >> >> Hi, Lv Zheng.
> >> >>
> >> >> I added my handcrafted ACPI table under your request, because
> >> >> "acpidump -c on" and "acpidump -c off" doesn't work.
> >> >>
> >> >> 2017-02-21 19:36 GMT+09:00 Seunghun Han <kkamagui@...il.com>:
> >> >> > Hello,
> >> >> >
> >> >> > I attached the test results below,
> >> >> >
> >> >> > 2017-02-21 9:53 GMT+09:00 Rowafael J. Wysocki <rjw@...ysocki.net>:
> >> >> >> On Tuesday, February 21, 2017 12:33:08 AM Zheng, Lv wrote:
> >> >> >>> Hi,
> >> >> >>>
> >> >> >>> > From: linux-acpi-owner@...r.kernel.org [mailto:linux-acpi-owner@...r.kernel.org] On Behalf Of Seunghun
> >> >> >>> > Han
> >> >> >>> > Subject: [PATCH v2] acpi: acpica: fix acpi operand cache leak
> >> >> >>> >
> >> >> >>> > I'm Seunghun Han, and I work for National Security Research Institute of
> >> >> >>> > South Korea.
> >> >> >>> >
> >> >> >>> > I have been doing a research on ACPI and making a handcrafted ACPI table
> >> >> >>> > for my research.
> >> >> >>> > Errors of handcrafted ACPI tables are handled well in Linux kernel while boot
> >> >> >>> > process, and Linux kernel goes well without critical problems.
> >> >> >>> > But I found some ACPI operand cache leaks in ACPI early abort cases.
> >> >> >>> >
> >> >> >>> > Boot log of ACPI operand cache leak is as follows:
> >> >> >>> > >[    0.174332] ACPI: Added _OSI(Module Device)
> >> >> >>> > >[    0.175504] ACPI: Added _OSI(Processor Device)
> >> >> >>> > >[    0.176010] ACPI: Added _OSI(3.0 _SCP Extensions)
> >> >> >>> > >[    0.177032] ACPI: Added _OSI(Processor Aggregator Device)
> >> >> >>> > >[    0.178284] ACPI: SCI (IRQ16705) allocation failed
> >> >> >>> > >[    0.179352] ACPI Exception: AE_NOT_ACQUIRED, Unable to install System Control Interrupt handler
> >> >> >>> > (20160930/evevent-131)
> >> >> >>> > >[    0.180008] ACPI: Unable to start the ACPI Interpreter
> >> >> >>> > >[    0.181125] ACPI Error: Could not remove SCI handler (20160930/evmisc-281)
> >> >> >>> > >[    0.184068] kmem_cache_destroy Acpi-Operand: Slab cache still has objects
> >> >> >>> > >[    0.185358] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.10.0-rc3 #2
> >> >> >>> > >[    0.186820] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
> >> >> >>> > >[    0.188000] Call Trace:
> >> >> >>> > >[    0.188000]  ? dump_stack+0x5c/0x7d
> >> >> >>> > >[    0.188000]  ? kmem_cache_destroy+0x224/0x230
> >> >> >>> > >[    0.188000]  ? acpi_sleep_proc_init+0x22/0x22
> >> >> >>> > >[    0.188000]  ? acpi_os_delete_cache+0xa/0xd
> >> >> >>> > >[    0.188000]  ? acpi_ut_delete_caches+0x3f/0x7b
> >> >> >>> > >[    0.188000]  ? acpi_terminate+0x5/0xf
> >> >> >>> > >[    0.188000]  ? acpi_init+0x288/0x32e
> >> >> >>> > >[    0.188000]  ? __class_create+0x4c/0x80
> >> >> >>> > >[    0.188000]  ? video_setup+0x7a/0x7a
> >> >> >>> > >[    0.188000]  ? do_one_initcall+0x4e/0x1b0
> >> >> >>> > >[    0.188000]  ? kernel_init_freeable+0x194/0x21a
> >> >> >>> > >[    0.188000]  ? rest_init+0x80/0x80
> >> >> >>> > >[    0.188000]  ? kernel_init+0xa/0x100
> >> >> >>> > >[    0.188000]  ? ret_from_fork+0x25/0x30
> >> >> >>>
> >> >> >>> I'm more interested in the way of triggering AE_NOT_ACQUIRED error.
> >> >> >>> So could you send us the handcrafted ACPI table or both the "acpidump -c on" and "acpidump -c off" output?
> >> >>
> >> >> I modified FACP, FACS, APIC table in VirtualBox for Linux.
> >> >> Here are raw dumps of table.
> >> >
> >> > So, excuse me, but what's the security issue here?
> >> >
> >> > You hacked your ACPI tables into pieces which requires root privileges anyway.
> >> >
> >> > Thanks,
> >> > Rafael
> >> >
> >>
> >> As you mentioned earlier, I hacked my ACPI table for research, so it seems that
> >> it is not a security issue.
> >>
> >> But, if new mainboard are released and they have a vendor-specific ACPI table
> >> which has invalid data, the old version of kernel (<=4.9) will possibly expose
> >> kernel address and KASLR will be neutralized unintentionally.
> >
> > But that would mean a basically non-functional system, so I'm not sure how
> > anyone can actually take advantage of the "KASLR neutralization".
> 
> I think an attacker can take advantage of the "KASLR neutralization". As you
> know, KASLR is good technology to protect kernel from kernel exploits.
> 
> If the kernel has vulnerabilities, the attacker can make exploit using them.
> But, the exploit usually needs gadgets (small code), therefore the attacker
> should know where the gadgets are in kernel. If the KASLR is working in kernel,
> the attacker should find the actual kernel address, and he can get kernel
> address information from kernel warning.

If the system basically doesn't work, that information isn't  particularly useful.

> >> I know the vendors collaborate with Linux kernel developers, but the problem
> >> can still occur.
> >>
> >> Hardware vendors release so many kinds of mainboard in a year, and the major
> >> Linux distros (Ubuntu, Fedora, etc.) will have 4.8 kernel for a long time.
> >>
> >> For this reason, I think this issue has a security aspect.
> >
> > Well, not quite IMO.
> >
> > If the system needs ACPI tables and the kernel cannot use them, it just won't
> > work no matter what.
> >
> > Thanks,
> > Rafael
> >
> Yes, you are right. But, Linux kernel has well-defined exception handlers, so
> some systems may work fine like my test machine. Moreover the users may not
> recognize what the problem is, and I think that they will use the system in
> insecure status for a long time.

A virtual box or a guest can run without ACPI tables.  A bare metal system
where ACPI tables are necessary will be more-or-less unusable if the kernel
cannot use them (it won't be able to detect interrupt controllers and the PCI
host bridge just for starters).

Running a guest with totally broken ACPI tables requires root privileges on the
host.  Running a bare metal system with totally broken ACPI tables (which seems
to be your basic concern) may be a good research project, but nobody will do
that in practice.  And everybody who tries that will notice what's going on.

Yes, you found a bug, but I still am not convinced about how this is security-related.

Thanks,
Rafael

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