Out-of-the-box SPD support
an invention by jdelvare
Updated almost 4 years ago. 1 hackers ♥️. 2 followers.

In order to see the SPD (detailed memory information) data, the user currently has to manually load the needed kernel driver. Which driver to load depends on the memory type. Depending on the driver user, the devices may even have to be instantiated manually and this is a non-trivial multi-step task. Plus you need to be root to do it.

I would like to attempt to automatize all this at least in the most common and simple cases like Intel x86 desktop. The idea would be to figure out the memory type and the I2C address of the SPD EEPROMs based on DMI data. If the DMI data is of good quality then it should be possible to automatically figure out which driver to use and to instantiate the devices at boot time.

If this works then running "decode-dimms" (or any other equivalent tool) should just work after boot without any preparatory work, for all users.

I plan to start implementing this for DDR3 memory and the i2c-i801 SMBus controller driver because that's what I have on my workstation. If it works, doing the same for DDR4 shouldn't be too difficult. Once this works for the i2c-i801, it should be pretty trivial to do the same with other SMBus controller drivers, for example i2c-piix4.

Excluded from the scope are large server systems with multiple SMBus controllers or multiplexed SMBus. Also excluded are OF/DT systems as I would expect SPD EEPROMs to be declared in the device tree so they would already be instantiated without further effort.

Looking for hackers with the skills:

i2c-tools kernel smbus dmi

This project is part of:

Hack Week 18

Activity

  • almost 5 years ago: jdelvare started this project.
  • over 5 years ago: a_faerber liked this project.
  • over 5 years ago: jdelvare added keyword "i2c-tools" to this project.
  • over 5 years ago: jdelvare added keyword "kernel" to this project.
  • over 5 years ago: jdelvare added keyword "smbus" to this project.
  • over 5 years ago: jdelvare added keyword "dmi" to this project.
  • over 5 years ago: jdelvare originated this project.


    • Comments

    • jdelvare
      almost 4 years ago by jdelvare | Reply

      For the record, this hack week project was successful. Relevant upstream kernel commits:

      commit 9e0afe3910ff7e5493c5d8ebe3b499994b5e0272
Author: Jean Delvare 
Date:   Tue Dec 3 11:20:37 2019 +0100

    firmware: dmi: Remember the memory type

commit 7c2378800cf7ac87e2663afa7f39d102871f0c28
Author: Jean Delvare 
Date:   Tue Dec 3 11:20:37 2019 +0100

    firmware: dmi: Add dmi_memdev_handle

commit 5ace60859e84113b7a185c117fbf2c429d381b59
Author: Jean Delvare 
Date:   Mon Mar 16 11:22:24 2020 +0100

    i2c: smbus: Add a way to instantiate SPD EEPROMs automatically

commit 01590f361e94a01e9b9868fa81d4079d255c681f
Author: Jean Delvare 
Date:   Mon Mar 16 11:24:48 2020 +0100

    i2c: i801: Instantiate SPD EEPROMs automatically

      So the feature is supported since kernel v5.8. Next step is to extend support to systems with 5-8 memory slots (still on a single SMBus segment), and to add support to other SMBus controller drivers.

    Similar Projects

    Model checking the BPF verifier by shunghsiyu

    Project Description

    BPF verifier plays a crucial role in securing the system (though less so now that unprivileged BPF is disabled by default in both upstream and SLES), and bugs in the verifier has lead to privilege escalation vulnerabilities in the past (e.g. CVE-2021-3490).

    One way to check whether the verifer has bugs to use model checking (a formal verification technique), in other words, build a abstract model of how the verifier operates, and then see if certain condition can occur (e.g. incorrect calculation during value tracking of registers) by giving both the model and condition to a solver.

    For the solver I will be using the Z3 SMT solver to do the checking since it provide a Python binding that's relatively easy to use.

    Goal for this Hackweek

    Learn how to use the Z3 Python binding (i.e. Z3Py) to build a model of (part of) the BPF verifier, probably the part that's related to value tracking using tristate numbers (aka tnum), and then check that the algorithm work as intended.

    Resources

    Contributing to Linux Kernel security by pperego

    Description

    A couple of weeks ago, I found this blog post by Gustavo Silva, a Linux Kernel contributor.

    I always strived to start again into hacking the Linux Kernel, so I asked Coverity scan dashboard access and I want to contribute to Linux Kernel by fixing some minor issues.

    I want also to create a Linux Kernel fuzzing lab using qemu and syzkaller

    Goals

    1. Fix at least 2 security bugs
    2. Create the fuzzing lab and having it running

    The story so far

    • Day 1: setting up a virtual machine for kernel development using Tumbleweed. Reading a lot of documentation, taking confidence with Coverity dashboard and with procedures to submit a kernel patch
    • Day 2: I read really a lot of documentation and I triaged some findings on Coverity SAST dashboard. I have to confirm that SAST tool are great false positives generator, even for low hanging fruits.
    • Day 3: Working on trivial changes after I read this blog post: https://www.toblux.com/posts/2024/02/linux-kernel-patches.html. I have to take confidence with the patch preparation and submit process yet.
      • First trivial patch sent: using strtruefalse() macro instead of hard-coded strings in a staging driver for a lcd display
      • Fix for a dereference before null check issue discovered by Coverity (CID 1601566) https://scan7.scan.coverity.com/#/project-view/52110/11354?selectedIssue=1601566
    • Day 4: Triaging more issues found by Coverity.
      • The patch for CID 1601566 was refused. The check against the NULL pointer was pointless so I prepared a version 2 of the patch removing the check.
      • Fixed another dereference before NULL check in iwlmvmparsewowlaninfo_notif() routine (CID 1601547). This one was already submitted by another kernel hacker :(
    • Day 5: Wrapping up. I had to do some minor rework on patch for CID 1601566. I found a stalker bothering me in private emails and people I interacted with me, advised he is a well known bothering person. Markus Elfring for the record.

    • Wrapping up: being back doing kernel hacking is amazing and I don't want to stop it. My battery pack is completely drained but changing the scope gave me a great twist and I really want to feel this energy not doing a single task for months.

      I failed in setting up a fuzzing lab but I was too optimistic for the patch submission process.

    The patches

    1

    early stage kdump support by mbrugger

    Project Description

    When we experience a early boot crash, we are not able to analyze the kernel dump, as user-space wasn't able to load the crash system. The idea is to make the crash system compiled into the host kernel (think of initramfs) so that we can create a kernel dump really early in the boot process.

    Goal for the Hackweeks

    1. Investigate if this is possible and the implications it would have (done in HW21)
    2. Hack up a PoC (done in HW22 and HW23)
    3. Prepare RFC series (giving it's only one week, we are entering wishful thinking territory here).

    update HW23

    • I was able to include the crash kernel into the kernel Image.
    • I'll need to find a way to load that from init/main.c:start_kernel() probably after kcsan_init()
    • I workaround for a smoke test was to hack kexec_file_load() systemcall which has two problems:
      1. My initramfs in the porduction kernel does not have a new enough kexec version, that's not a blocker but where the week ended
      2. As the crash kernel is part of init.data it will be already stale once I can call kexec_file_load() from user-space.

    The solution is probably to rewrite the POC so that the invocation can be done from init.text (that's my theory) but I'm not sure if I can reuse the kexec infrastructure in the kernel from there, which I rely on heavily.

    update HW24

    • Day1
      • rebased on v6.12 with no problems others then me breaking the config
      • setting up a new compilation and qemu/virtme env
      • getting desperate as nothing works that used to work
    • Day 2
      • getting to call the invocation of loading the early kernel from __init after kcsan_init()

    • Day 3

      • fix problem of memdup not being able to alloc so much memory... use 64K page sizes for now
      • code refactoring
      • I'm now able to load the crash kernel
      • When using virtme I can boot into the crash kernel, also it doesn't boot completely (major milestone!), crash in elfcorehdr_read_notes()

    • Day 4

      • crash systems crashes (no pun intended) in copy_old_mempage() link; will need to understand elfcorehdr...
      • call path vmcore_init() -> parse_crash_elf_headers() -> elfcorehdr_read() -> read_from_oldmem() -> copy_oldmem_page() -> copy_to_iter()

    • Day 5

      • hacking arch/arm64/kernel/crash_dump.c:copy_old_mempage() to see if crash system really starts. It does.
      • fun fact: retested with more reserved memory and with UEFI FW, host kernel crashes in init but directly starts the crash kernel, so it works (somehow) \o/

    • TODOs

      • fix elfcorehdr so that we actually can make use of all this...
      • test where in the boot __init() chain we can/should call kexec_early_dump()

    Improve UML page fault handler by ptesarik

    Description

    Improve UML handling of segmentation faults in kernel mode. Although such page faults are generally caused by a kernel bug, it is annoying if they cause an infinite loop, or panic the kernel. More importantly, a robust implementation allows to write KUnit tests for various guard pages, preventing potential kernel self-protection regressions.

    Goals

    Convert the UML page fault handler to use oops_* helpers, go through a few review rounds and finally get my patch series merged in 6.14.

    Resources

    Wrong initial attempt: https://lore.kernel.org/lkml/20231215121431.680-1-petrtesarik@huaweicloud.com/T/

    Officially Become a Kernel Hacker! by m.crivellari

    Description

    My studies as well my spare time are dedicated to the Linux Kernel. Currently I'm focusing on interrupts on x86_64, but my interests are not restricted to one specific topic, for now.

    I also "played" a little bit with kernel modules (ie lantern, a toy packet analyzer) and I've added a new syscall in order read from a task A, the memory of a task B.

    Maybe this will be a good chance to...

    Goals

    • create my first kernel patch

    Resources

    Achivements