Re: [RFC] Proposal: Static SECCOMP Policies

[Neill Kapron <nkapron@google.com>]

On Thu, Sep 12, 2024 at 04:02:53PM +0000, Maxwell Bland wrote:
> (Resending as plaintext for msm-kernel mailing list.
> Original message was intended for android kernel team
> though msm-kernel should be aware.)
> 
> Hi Kernel Team,
> 
> + Kees, Andy, and Will since their input may be valuable.
> 
> It has been a while! (~9 months to be exact). This January, I sent out a small
> message on BPF code loading ("unprivileged BPF considered harmful" or something
> like that). In it, I noted new BPF programs are compiled all the time and
> thrown into the kernel. At the time, I did not know these programs were just
> compiled seccomp filter policies, loaded in as new BPF programs continuously
> through the libminijail interface as well as direct syscall. As of two days
> ago, I now know this (and now you do too, if not already).
> 
> OK, yes, syscall filtering is very important, but this is creating a catch-22
> issue. For one, see step (4) under "Exploitation overview" for
> https://www.qualys.com/2021/07/20/cve-2021-33909/sequoia-local-privilege-escalation-linux.txt.
> Second, this minor lack of caching is adding load time to more than 90
> binaries/services on the standard QCOM baseline—I'll admit, it is probably
> negligible in the grand scheme of things (a quick approximation puts the data
> operated on around 0.1188 MB). But most importantly, third, without some degree
> of provenance, I have no way of telling if someone has injected malicious code
> into the kernel, and unfortunately even knowing the correct bytes is still
> "iffy", as in order to prevent JIT spray attacks, each of these filters is
> offset by some random number of uint32_t's, making every 4-byte shift of the
> filter a "valid" codepage to be loaded at runtime.
> 
> You might be thinking, "but wait, bionic's libc only defines a couple of
> restricted policies, primary and secondary for system and user apps
> respectively." I know! For the most part, apps fall into either what I presume
> is the default app/system policies, but there are lots of QCOM binaries and
> other magic programs (dolby dax) that are sending up these programs as well.
> I'm seeing more than 20 different programs for around a minute's worth of
> runtime. One example is attached at the end.
> 
> So, the proposal: a "CONFIG_SECCOMMP_STATIC_POLICY" for seccomp. This
> would change the Android kernel's generic SYS_seccomp call, which takes in a
> filter with an array of BPF instructions, to instead reference an ID which
> corresponds to a fixed file on /sys/bpf/seccomp or something like that. The
> sandboxing behavior of these apps should be known at compile-time, even if
> there are multiple "permission set types" that may need to be dispatched. User
> apps should always have a single, fixed policy. This way it is possible to say
> for every code page loaded into the kernel where it came from and what it
> should look like.
> 
> Unfortunately, I do not know Motorola has enough "weight" to convince QCOM to
> do the right foundational thing here, or to "define" the seccomp APIs for
> Android, so it would be good to have Google's buy in, know if there are plans
> to fix this issue, or some discussion of how to best fix the problem? If
> anything, a contact at QCOM that might be able to actually hunt down and
> document valid bytes for these policies?
> 
> The end goal is simple: when we see a code page is allocated in the kernel, we
> can be sure that (1) it isn't malicious and (2) has not been modified in
> transit. I'm fine putting code where my mouth is, but right now that code
> would involve having to fingerprint the signatures loaded by Qualcomm
> components every time a new one is released, or pinging Google with a huge
> patch changing how seccomp works with no idea of what requirements QCOM may
> have on seccomp policy generation.
> 
> Thoughts? Is this doable, and if not, why? I'd also love help with the code and
> adapting existing minijail code to use a new, more integrity-preserving
> interface. If I am mistaken and it is possible to grab out valid BPF policy
> code at compile time, please let me know how!
> 
> Regards,
> Maxwell Bland
> 
> Standard filter, (from, for example, com.google.android.gms)
> "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",
> Unknown filter (from QCOM's /vendor/bin/qesdk-secmanager)
>  "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",
> 
> List of services loading seccomp filters pulled from one run of the phone:
> com.google.android.deskclock
> /vendor/bin/qesdk-secmanager
> media.hwcodec/vendor.qti.media.c2@1.0-service
> media.audio.qc.codec.qti.media.c2audio@1.0-service
> /vendor/bin/vendor.qti.qspmhal-service
> /vendor/bin/qsap_sensors
> media.extractoraextractor
> /system_ext/bin/perfservice
> /vendor/bin/wfdhdcphalservice
> /vendor/bin/wifidisplayhalservice
> /vendor/bin/qsap_dcfd
> /vendor/bin/qms
> /vendor/bin/qsap_location
> /vendor/bin/qsap_qapeservice
> /vendor/bin/wfdvndservice
> media.swcodecoid.media.swcodec/bin/mediaswcodec
> /vendor/bin/hw/qcrilNrd
> qsap_qms_13qms16
> qsap_qms_24qms17
> /vendor/bin/ATFWD-daemon
> /vendor/bin/hw/sxrservice
> /vendor/bin/hw/qcrilNrd-c2
> system_server
> /vendor/bin/qmi_motext_hook1013170
> /vendor/bin/qmi_motext_hook1013171
> /vendor/bin/ims_rtp_daemon
> com.android.systemui
> webview_zygote
> com.dolby.daxservice
> vendor.qti.qesdk.sysservice
> org.codeaurora.ims
> com.android.se
> com.android.phone
> com.qti.qcc
> com.google.android.ext.services
> com.google.android.gms
> com.google.android.euicc
> com.google.android.googlequicksearchbox:interactor
> com.google.android.apps.messaging:rcs
> com.android.nfc
> com.qualcomm.qti.workloadclassifier
> com.qualcomm.location
> com.google.android.gms.unstable
> com.thundercomm.ar.core
> com.android.vending:background
> com.android.vending:quick_launch
> com.android.dynsystem
> com.android.managedprovisioning
> com.android.shell


+ Jeff, Alistair, and Maciej

Maxwell,

Thanks for the details on this, I have added several people who may be
better suited to comment on this.

Neill