Re: [PATCH v2] acpi: acpica: fix acpi operand cache leak

[Seunghun Han]

Hello, Lv and Rafael.

I checked that my patch was merged to ACPICA project.
Thank you for your notice.

I added an analysis report which has the root cause of this problem below.

2017-02-27 11:45 GMT+09:00 Zheng, Lv <lv.zheng@xxxxxxxxx>:
> Hi, Rafael
>
>> From: linux-acpi-owner@xxxxxxxxxxxxxxx [mailto:linux-acpi-owner@xxxxxxxxxxxxxxx] On Behalf Of Rafael J.
>> Wysocki
>> Subject: Re: [PATCH v2] acpi: acpica: fix acpi operand cache leak
>>
>> On Fri, Feb 24, 2017 at 11:37 PM, Seunghun Han <kkamagui@xxxxxxxxx> wrote:
>> > Hi, Rafael.
>> >
>> > I agree with you and I added my opinion below.
>> >
>> > 2017-02-25 1:50 GMT+09:00 Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>:
>> >> 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@xxxxxxxxxxxxx>:
>> >>> > 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@xxxxxxxxxxxxx>:
>> >>> >> > 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@xxxxxxxxx>:
>> >>> >> >> > Hello,
>> >>> >> >> >
>> >>> >> >> > I attached the test results below,
>> >>> >> >> >
>> >>> >> >> > 2017-02-21 9:53 GMT+09:00 Rowafael J. Wysocki <rjw@xxxxxxxxxxxxx>:
>> >>> >> >> >> On Tuesday, February 21, 2017 12:33:08 AM Zheng, Lv wrote:
>> >>> >> >> >>> Hi,
>> >>> >> >> >>>
>> >>> >> >> >>> > From: linux-acpi-owner@xxxxxxxxxxxxxxx [mailto:linux-acpi-owner@xxxxxxxxxxxxxxx] 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.
>> >
>> > I totally agree with you that this case is not in practice now.
>> > I just started researching on ACPI, and I don't have enough ideas to occur
>> > a security problem using a bug. I just think that it has a little possibility
>> > which is security-related.
>> >
>> > Thank you so much for your guides.
>> > It helps me a lot to change my research direction.
>> >
>> > So, could my patch be merged in next kernel (4.11 rc-1)? or do I need to do
>> > something for it?
>> > Please let me know.
>>
>> Generally, ACPICA patches (and this is one of them) have to go in via
>> the upstream ACPICA project maintained by Bob Moore and Lv.  Please
>> see MAINTAINERS for pointers to the mailing list etc.
>>
>> Lv, can you please advise on the next steps?
>
> I already gave my advices.
> The fix was OK to me and I back ported it to ACPICA:
> https://github.com/acpica/acpica/pull/206
> However it fixes a code path that in theory shouldn't be invoked in Linux kernel.
> But anyway it was merged and you will see it in the next ACPICA release.
>
> I asked Han for the handcrafted ACPI table.
> And obtained that:
> ACPI: FACP 0x00000000DFFF00F0 0000F4 (v04 VBOX VBOXFACP 00000001 ASL  00000061)
> 0x0000: 46 41 43 50 F4 00 00 00 04 60 56 42 4F 58 20 20
> 0x0010: 56 42 4F 58 46 41 43 50 01 00 00 00 41 53 4C 20
> 0x0020: 61 00 00 00 00 02 FF DF 80 04 FF DF 41 41 41 41
> 0x0030: 2E 44 00 00 A1 A0 00 00 00 40 00 00 00 00 00 00
> 0x0040: 04 40 00 00 00 00 00 00 00 00 00 00 08 40 00 00
> 0x0050: 20 40 00 00 00 00 00 00 04 02 00 04 02 00 00 00
> 0x0060: 65 00 E9 03 00 00 00 00 00 00 00 00 00 03 00 00
> 0x0070: 41 05 00 00 01 08 00 01 50 40 00 00 00 00 00 00
> 0x0080: 10 00 00 00 00 02 FF DF 00 00 00 00 80 04 FF DF
> 0x0090: 00 00 00 00 01 20 00 02 00 40 00 00 00 00 00 00
> 0x00A0: 00 00 00 00 00 00 00 00 00 00 00 00 01 10 00 02
> 0x00B0: 04 40 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 0x00C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 0x00D0: 01 20 00 03 08 40 00 00 00 00 00 00 01 10 00 01
> 0x00E0: 20 40 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 0x00F0: 00 00 00 00
>
> ACPI: FACS 0x00000000DFFF0200 000040
> 0x0000: 46 41 43 53 40 00 00 00 00 00 00 00 00 00 00 00
> 0x0010: 00 00 00 00 00 00 00 00 00 41 41 41 41 41 41 41
> 0x0020: 01 00 00 00 00 00 00 00 00 41 00 00 00 00 00 00
> 0x0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>
> ACPI: APIC 0x00000000DFFF0240 00006C (v02 VBOX VBOXAPIC 00000001 ASL  00000061)
> 0x0000: 41 50 49 43 6C 00 00 00 02 21 56 42 4F 58 20 20
> 0x0010: 56 42 4F 58 41 50 49 43 01 00 00 00 41 53 4C 20
> 0x0020: 61 00 00 00 00 00 E0 FE 01 00 00 00 02 0A 00 00
> 0x0030: 02 00 00 00 00 00 02 0A 00 09 09 00 00 00 0D 00
> 0x0040: 00 08 00 00 01 00 41 41 41 41 41 41 41 41 41 00
> 0x0050: 00 08 02 02 01 00 00 00 00 08 03 03 01 00 00 00
> 0x0060: 01 0C 04 00 00 00 C0 FE 00 00 00 00
>
> Where there is still no AML tables and the failure in the patch description seems to be related to the AML tables.
> So I'm still not aware of what the "handcrafted tables" meant to us and what the problem was.

Actually, I did not change DSDT and SSDT. I changed only FACP, FACS and APIC for
my handcrafted ACPI table.

I have analyzed the root cause of the problem, and I have found that my
handcrafted ACPI table has too big SCI IRQ (like 16705).
So, acpi_os_install_interrupt_handler() which is called by
acpi_enable_subsystem()
was failed and returned AE_NOT_ACQUIRED (0x14) with "ACPI: SCI (IRQ16705)
allocation failed" log.

Because of error code, acpi_bus_init(), the caller of acpi_enable_subsystem(),
showed "Unable to start the ACPI Interpreter" and called acpi_terminate() for
exception handling. After calling acpi_terminate(), as you know, cache leak
occurred.
This means that error of acpi_load_tables(), acpi_initialize_objects(),
acpi_bus_init_irq() and acpi_install_notify_handler() which are called by
acpi_bus_init() can cause cache leak.

If you want to see this error handling sequence, I suggest you that you change
the code of acpi_os_install_interrupt_handler() to return AE_NOT_ACQUIRED
immediately. Then, you can see the error handling sequence without my
handcrafted
ACPI table.

I you want additional information about this, please let me know.

Best regards.

>
> Thanks and best regards
> Lv
>
>>
>> Thanks,
>> Rafael
>> --
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