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

[Rafael J. Wysocki]

On Monday, February 27, 2017 02:45:50 AM Zheng, Lv wrote:
> 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.

Thank you!

Best,
Rafael