4 ms·

Description of the CVE: > Improper validation in a model specific register (MSR) could allow a malicious program with ring0 access to modify SMM configuration

Description of the CVE: > Improper validation in a model specific register (MSR) could allow a malicious program with ring0 access to modify SMM configuration while SMI lock is enabled, potentially leading to arbitrary code execution.

AnimalMuppet 2y ago
OK, but... if a malicious program has ring0 access, isn't it game over anyway?
- gruez 2y ago
  https://xkcd.com/1200/ https://xkcd.com/1200/
- bastawhiz 2y ago
  Not offering an opinion either way, but it depends. If you can exploit the kernel, you can probably do whatever you want. But if you manage to exploit the CPU firmware, you can do what you want even after the system is completely wiped. Whether you think someone is motivated enough to find a kernel exploit that can trigger this issue and then go through the trouble of exploiting not just the kernel but this very specific CPU issue that exists on certain processors is up to you. Is it likely? I'd say no. Is it possible? Yes. Should you care? Yes. Should you lose sleep? Probably not.
  - sqeaky 2y ago
    Oh my god, is this a level headed comment based on the actual technical merit?!
  - binary132 2y ago
    The authors of Stuxnet were “motivated enough” and had the means at their disposal to do what they did. I’m just saying, where the motivate and means exist, it’s possible.
    - nothercastle 2y ago
      You can’t protect against a state level actor. They could just get physical access in most cases anyway and force got to give up the codes
      - binary132 2y ago
        You’re assuming a domestic state actor, no? I don’t think it’s a positive certainty that e.g. a foreign state will certainly be able to physically access your systems. Of course, I suppose if you send it in to a foreign country for repair, anything can happen.
        readthenotes1 2y ago
        If properly motivated, I don't think national boundaries are going to stop someone from accessing a physical device. There may be a small list of countries with very good border controls and lack of existing foreign agents. I'd be curious to know which ones fit
    - bastawhiz 2y ago
      I'm not disagreeing with you. That said, Stuxnet was built by a state actor with the motivation to target nuclear industrial equipment, not your media server's Ryzen 3000. It would be an hell of a lot of motivation without obvious payoff to use this vulnerability to, say, make nastier ransomware or steal crypto. The novelty of this exploit is the durability of it (persisting beyond a full wipe), which isn't something your garden-variety malware needs to extract value. If you have ring0, you already won. If you're a person who needs to be careful about this sort of stuff (e.g., you're Edward Snowden or run Iran's nuclear program), you hopefully are already paying attention. If you are a mere muggle like the rest of us, the risk is probably not high enough for you to get upset.
      - binary132 2y ago
        I don’t think it’s so crazy to think about the fact that tools like this can be both used by, _and designed for the use of_ state actors, whether in actions against other governments or troublesome individuals — for example, Pegasus is not only for state actors.
- outworlder 2y ago
  Yes, but generally speaking they can be removed if you wipe the system.
- mjg59 2y ago
  Getting into SMM means you can circumvent flash protection, which means you can rewrite the firmware to backdoor the OS on every boot without needing to leave any evidence in the filesystem, which a normal compromise of ring 0 wouldn't. I don't think most people need to worry about this, but if the claims are accurate this is a genuine circumvention of a privilege boundary.
  - broknbottle 2y ago
    No need to speculate and worry about this sort of thing, PC manufacturers have been doing this for years.. https://www.techdirt.com/2015/08/13/lenovo-busted-stealthily-installing-crapware-via-bios-fresh-windows-installs/ https://www.techdirt.com/2015/08/13/lenovo-busted-stealthily... https://www.dell.com/support/kbdoc/en-us/000130396/what-is-absolute https://www.dell.com/support/kbdoc/en-us/000130396/what-is-a... https://i.dell.com/sites/content/business/solutions/brochures/en/Documents/absolute-computrace-security.pdf https://i.dell.com/sites/content/business/solutions/brochure...
  - ori_b 2y ago
    Yeah. it sounds like SMM was a mistake, and we should have a user-controlled OS at that level (or, nothing at all).
- paulmd 2y ago
  no, that is the whole point of the Secure Encrypted Virtualization hypervisor (and remember, bare-metal is just another guest). Guests should not be able to jump to hypervisor control just because they type sudo, or just because they have physical presence. this all comes from the work AMD did on the xbox hypervisor, and obviously a console needs to be physically present (sitting in the attacker's living room) and survive a complete compromise of a guest partition (again, potentially including the OS/"bare-metal guest"). https://www.youtube.com/watch?v=U7VwtOrwceo https://www.youtube.com/watch?v=U7VwtOrwceo why would ring0 ever be intended to grant you access to ring -1 or -2? why even have rings -1 or -2 in that situation?
  - ndriscoll 2y ago
    When the owner of the device is the "attacker", "why even have this" is indeed a good question.
    - paulmd 2y ago
      well, like it or not that's a real use-case - and not just DRM/anti-cheat but also things like homomorphic encryption. there's lots of interest in being able to do useful things when the owner of the machine might be an attacker, that is an extremely broad and useful primitive to build upon. secure encrypted virtualization is supposed to be "homomorphic encryption, but in a system we can actually implement/that actually performs decently". obviously it would be reassuring to know that hetzner can't look at your data that you put into the hardware they own, right? how do you accomplish that if not creating a root-of-trust that's not controlled by the owner of the machine? I don't trust Hetzner to not see my data, but I might be willing to trust AMD. Let AMD hold the key to my VM memory partition, and the hypervisor exists in a different VM memory partition, and its keys don't work in my partition. Things which break that security model are obviously of huge concern and it feels borderline intentionally-misleading to phrase it as "why would you be concerned about that". The answer is because it's a foundational break in the security model of SEV and the PSP.
      - ndriscoll 2y ago
- fsflover 2y ago
  Not if you run Qubes OS, for example.

AnimalMuppet 2y ago

OK, but... if a malicious program has ring0 access, isn't it game over anyway?

gruez 2y ago
https://xkcd.com/1200/ https://xkcd.com/1200/
bastawhiz 2y ago
Not offering an opinion either way, but it depends. If you can exploit the kernel, you can probably do whatever you want. But if you manage to exploit the CPU firmware, you can do what you want even after the system is completely wiped. Whether you think someone is motivated enough to find a kernel exploit that can trigger this issue and then go through the trouble of exploiting not just the kernel but this very specific CPU issue that exists on certain processors is up to you. Is it likely? I'd say no. Is it possible? Yes. Should you care? Yes. Should you lose sleep? Probably not.
- sqeaky 2y ago
  Oh my god, is this a level headed comment based on the actual technical merit?!
- binary132 2y ago
  The authors of Stuxnet were “motivated enough” and had the means at their disposal to do what they did. I’m just saying, where the motivate and means exist, it’s possible.
  - nothercastle 2y ago
    You can’t protect against a state level actor. They could just get physical access in most cases anyway and force got to give up the codes
    - binary132 2y ago
      You’re assuming a domestic state actor, no? I don’t think it’s a positive certainty that e.g. a foreign state will certainly be able to physically access your systems. Of course, I suppose if you send it in to a foreign country for repair, anything can happen.
      - readthenotes1 2y ago
        If properly motivated, I don't think national boundaries are going to stop someone from accessing a physical device. There may be a small list of countries with very good border controls and lack of existing foreign agents. I'd be curious to know which ones fit
  - bastawhiz 2y ago
    I'm not disagreeing with you. That said, Stuxnet was built by a state actor with the motivation to target nuclear industrial equipment, not your media server's Ryzen 3000. It would be an hell of a lot of motivation without obvious payoff to use this vulnerability to, say, make nastier ransomware or steal crypto. The novelty of this exploit is the durability of it (persisting beyond a full wipe), which isn't something your garden-variety malware needs to extract value. If you have ring0, you already won. If you're a person who needs to be careful about this sort of stuff (e.g., you're Edward Snowden or run Iran's nuclear program), you hopefully are already paying attention. If you are a mere muggle like the rest of us, the risk is probably not high enough for you to get upset.
    - binary132 2y ago
      I don’t think it’s so crazy to think about the fact that tools like this can be both used by, _and designed for the use of_ state actors, whether in actions against other governments or troublesome individuals — for example, Pegasus is not only for state actors.
outworlder 2y ago
Yes, but generally speaking they can be removed if you wipe the system.
mjg59 2y ago
Getting into SMM means you can circumvent flash protection, which means you can rewrite the firmware to backdoor the OS on every boot without needing to leave any evidence in the filesystem, which a normal compromise of ring 0 wouldn't. I don't think most people need to worry about this, but if the claims are accurate this is a genuine circumvention of a privilege boundary.
- broknbottle 2y ago
  No need to speculate and worry about this sort of thing, PC manufacturers have been doing this for years.. https://www.techdirt.com/2015/08/13/lenovo-busted-stealthily-installing-crapware-via-bios-fresh-windows-installs/ https://www.techdirt.com/2015/08/13/lenovo-busted-stealthily... https://www.dell.com/support/kbdoc/en-us/000130396/what-is-absolute https://www.dell.com/support/kbdoc/en-us/000130396/what-is-a... https://i.dell.com/sites/content/business/solutions/brochures/en/Documents/absolute-computrace-security.pdf https://i.dell.com/sites/content/business/solutions/brochure...
- ori_b 2y ago
  Yeah. it sounds like SMM was a mistake, and we should have a user-controlled OS at that level (or, nothing at all).
paulmd 2y ago
no, that is the whole point of the Secure Encrypted Virtualization hypervisor (and remember, bare-metal is just another guest). Guests should not be able to jump to hypervisor control just because they type sudo, or just because they have physical presence. this all comes from the work AMD did on the xbox hypervisor, and obviously a console needs to be physically present (sitting in the attacker's living room) and survive a complete compromise of a guest partition (again, potentially including the OS/"bare-metal guest"). https://www.youtube.com/watch?v=U7VwtOrwceo https://www.youtube.com/watch?v=U7VwtOrwceo why would ring0 ever be intended to grant you access to ring -1 or -2? why even have rings -1 or -2 in that situation?
- ndriscoll 2y ago
  When the owner of the device is the "attacker", "why even have this" is indeed a good question.
  - paulmd 2y ago
    well, like it or not that's a real use-case - and not just DRM/anti-cheat but also things like homomorphic encryption. there's lots of interest in being able to do useful things when the owner of the machine might be an attacker, that is an extremely broad and useful primitive to build upon. secure encrypted virtualization is supposed to be "homomorphic encryption, but in a system we can actually implement/that actually performs decently". obviously it would be reassuring to know that hetzner can't look at your data that you put into the hardware they own, right? how do you accomplish that if not creating a root-of-trust that's not controlled by the owner of the machine? I don't trust Hetzner to not see my data, but I might be willing to trust AMD. Let AMD hold the key to my VM memory partition, and the hypervisor exists in a different VM memory partition, and its keys don't work in my partition. Things which break that security model are obviously of huge concern and it feels borderline intentionally-misleading to phrase it as "why would you be concerned about that". The answer is because it's a foundational break in the security model of SEV and the PSP.
    - ndriscoll 2y ago
fsflover 2y ago
Not if you run Qubes OS, for example.