4 ms·

TikTag: Breaking ARM's memory tagging extension with speculative execution

180 points by skilled 2y ago

skilled 2y ago
ARM has confirmed the possibility of an attack on systems with Cortex-X2, Cortex-X3, Cortex-A510, Cortex-A520, Cortex-A710, Cortex-A715 and Cortex-A720 processors, but does not intend to make changes to the CPU to block the problem[0], as how the MemTag architecture means that tags are not sensitive data to applications. Chrome's security team acknowledged the issues but won't fix them, as the V8 sandbox isn't designed for memory data confidentiality, and MTE defenses aren't enabled by default. It's mentioned quite early in the paper but there's a prototype toolkit on GitHub[1] if you want to jump straight into that. [0]: https://developer.arm.com/documentation/109544/latest https://developer.arm.com/documentation/109544/latest [1]: https://github.com/compsec-snu/tiktag https://github.com/compsec-snu/tiktag
- chc4 2y ago
  I'm not sure anyone is really surprised by this. Apple for example likewise calls out that you are at risk of an attacker using timing attacks to construct an authentication oracle for PAC, which is much more explicit about when exactly authentication checks actually happen.
wantedtoask 2y ago
My brain automatically thought this is "TikTok" -> Why would they release research on security if they are being targeted for security concerns
- codetrotter 2y ago
  > Why would they release research on security if they are being targeted for security concerns Hmm. That doesn’t really follow IMO. Every big corporation needs to have information security people. And most of them probably do some form of research as well. That’s the only way to stay on top of information security. Whether they publish anything or not is up to them. But it’d be super silly to base the decision for that on the fact that USA government is banning TikTok. By that line of argument, couldn’t you just as well say that they shouldn’t reveal that they hire infosec people either? Yet for example at https://careers.tiktok.com/m/position?category=6704215862603155720 https://careers.tiktok.com/m/position?category=6704215862603... they have several job openings relating to infosec such as this one: https://careers.tiktok.com/m/position/7379470900063095078/detail https://careers.tiktok.com/m/position/7379470900063095078/de... > The Global Security Organization provides industry-leading cyber-security and business protection services to TikTok globally. Our organization employs four principles that guide our strategic and tactical operations. Firstly, we Champion Transparency & Trust by leading the charge in organizational transparency, prioritizing customer trust, and placing user needs first. Secondly, we aim to maintain Best in Class Global Security by proactively identifying and reducing risks while enabling innovative product development. We constantly work towards a sustainable world-class security capability. Thirdly, we strive to be a Business Catalyst & Enabler by embodying the DNA of technical innovation and ensuring our Global Security operations are fast and agile. Heck here they even say just that: “proactively identifying and reducing risks while enabling innovative product development”. A natural part of that would be doing for example the kind of security researcher that the article of the OP is about.
Two4 2y ago
Going to need another one of these, Xe: https://xeiaso.net/shitposts/no-way-to-prevent-this/CVE-2024-4323/ https://xeiaso.net/shitposts/no-way-to-prevent-this/CVE-2024...
- saagarjha 2y ago
  This is not a bug caused by memory unsafe languages.
  - xena 2y ago
    The only exception is if the microcode responsible for this was written in C somehow. I highly doubt it though.
    - Two4 2y ago
      Oh no, I meant that this feature was made so people could continue to use memory-unsafe languages, but it turns out to be defeatable. If only there was some way to prevent this.
  - Two4 2y ago
    No, this is a feature created for memory-unsafe languages which has turned out to be yet another memory safety attack vector. But there's no way to prevent this.
    - akira2501 2y ago
      > for memory-unsafe languages And languages which require unsafe blocks to write any real system code. > But there's no way to prevent this There isn't. There are only mitigations. The environment is actively hostile. You can try to bake them in the hardware, which has huge up front design costs, and if a vulnerability is ever found, they become useless instantly. You can try to bake them into the language, which has moderate continual design costs, but if someone simply types 'unsafe' anywhere in your codebase they become useless instantly. You can try to enforce them in the frame work of your own code, which has moderate up front design costs, is possibly less reliable than the other methods, but they can be changed and redeployed when vulnerabilities are discovered. These problems don't go away simply because you made a particular hardware or language choice. You can't sweep this engineering under the rug and then act like your software is more secure than anything else.
seventyone 2y ago
"Confirmed the possibility" -- it was known when they invented this. https://infosec.exchange/@david_chisnall/112632040031740747 https://infosec.exchange/@david_chisnall/112632040031740747
- halJordan 2y ago
  Are you going to be posting the original shor's algorithm when the first quantum prime factorization hits the streets too?
dtx1 2y ago
> No problem, I was told, it’s not intended as a mitigation technique, it’s intended for at-scale debugging. Then certain companies decided it was a security technology. Yeah and it did work well for that usecase. https://grapheneos.social/@GrapheneOS/112066872276203917 https://grapheneos.social/@GrapheneOS/112066872276203917
gchadwick 2y ago
Does this actually have any real world implications? If you're using MTE you already know there's a simple attack that succeeds with 1/16th probability (or maybe greater if you reserve some tags for special purposes or have some exploitable pattern in how your allocator hands out tags). In that system this pushes the attack probability to 100%. A nice technique but (hopefully) you've already architectured things assuming MTE will be broken so this doesn't change anything. Certainly MTE was always pushed as a debugging feature only.
- vlovich123 2y ago
  > Certainly MTE was always pushed as a debugging feature only. This claim seems to come from ARM marketing but every SW company applying it - notably Google which I believe may have worked with ARM on this - mention of these types of tags in a security context (I believe Herb Sutter also talks about this as a way to harden c++ code). In fact, it’s seen as one very important way to harden existing legacy c/c++ code (and even unsafe Rust). There’s a big difference between 100% success rate and 1/16th - while you will still get an exploit through a 1/16th chance, the chances of detection raise significantly which isn’t nothing in a security context as it leaves a trail of breadcrumbs to investigate. > It will take more fundamental mitigations that address the root issue of memory corruption, like MTE, in order to dramatically raise the bar for attackers. https://googleprojectzero.blogspot.com/2024/06/driving-forward-in-android-drivers.html?m=1 https://googleprojectzero.blogspot.com/2024/06/driving-forwa... > Hardware memory tagging may fix some security pitfalls of C++, while still allowing high performance. We are looking forward to see a more broad adoption of hardware memory tagging in the future and suggest using Scan on top of hardware memory tagging to fix temporary memory safety for C++ https://security.googleblog.com/2022/05/retrofitting-temporal-memory-safety-on-c.html?m=1 https://security.googleblog.com/2022/05/retrofitting-tempora... Of course MTE + Scan described above may not be vulnerable to this attack, but my point stands that MTE is very much viewed as a memory safety hardening feature (and thus the security implications that come with safety hardening). This isn’t that bad news either. It may leave existing chips vulnerable but the next iteration of MTE will probably account for this problem (assuming you can’t patch microcode to solve this).
  - 2y ago
eigenform 2y ago
The authors' hypothesis about the STLF case: > Considering the affected core (i.e., Cortex-A715) dispatches 5 instructions in a cycle [ 55], it is likely that the CPU cannot detect the dependency if the store and load instructions are executed in the same cycle, since the store information is not yet written to the internal buffers. > If Len(GAP) is 4 or more, the store and load instructions are executed in the different cycles, and the CPU can detect the dependency. Therefore, the CPU skips the tag check and always forwards the data from the store to load instructions. > If Len(GAP) is less than 4, the store and load instructions are executed in the same cycle, and the CPU fails to detect the dependency and performs the tag check for the load instruction. In this case, the forwarding is blocked on tag check faults. This would mean there's no forwarding from stores to loads within the same dispatch group on these cores?
baybal2 2y ago
[dead]

180 points by skilled 2y ago

ARM has confirmed the possibility of an attack on systems with Cortex-X2, Cortex-X3, Cortex-A510, Cortex-A520, Cortex-A710, Cortex-A715 and Cortex-A720 processors, but does not intend to make changes to the CPU to block the problem[0], as how the MemTag architecture means that tags are not sensitive data to applications. Chrome's security team acknowledged the issues but won't fix them, as the V8 sandbox isn't designed for memory data confidentiality, and MTE defenses aren't enabled by default. It's mentioned quite early in the paper but there's a prototype toolkit on GitHub[1] if you want to jump straight into that. [0]: https://developer.arm.com/documentation/109544/latest https://developer.arm.com/documentation/109544/latest [1]: https://github.com/compsec-snu/tiktag https://github.com/compsec-snu/tiktag

chc4 2y ago
I'm not sure anyone is really surprised by this. Apple for example likewise calls out that you are at risk of an attacker using timing attacks to construct an authentication oracle for PAC, which is much more explicit about when exactly authentication checks actually happen.

wantedtoask 2y ago

My brain automatically thought this is "TikTok" -> Why would they release research on security if they are being targeted for security concerns

codetrotter 2y ago
> Why would they release research on security if they are being targeted for security concerns Hmm. That doesn’t really follow IMO. Every big corporation needs to have information security people. And most of them probably do some form of research as well. That’s the only way to stay on top of information security. Whether they publish anything or not is up to them. But it’d be super silly to base the decision for that on the fact that USA government is banning TikTok. By that line of argument, couldn’t you just as well say that they shouldn’t reveal that they hire infosec people either? Yet for example at https://careers.tiktok.com/m/position?category=6704215862603155720 https://careers.tiktok.com/m/position?category=6704215862603... they have several job openings relating to infosec such as this one: https://careers.tiktok.com/m/position/7379470900063095078/detail https://careers.tiktok.com/m/position/7379470900063095078/de... > The Global Security Organization provides industry-leading cyber-security and business protection services to TikTok globally. Our organization employs four principles that guide our strategic and tactical operations. Firstly, we Champion Transparency & Trust by leading the charge in organizational transparency, prioritizing customer trust, and placing user needs first. Secondly, we aim to maintain Best in Class Global Security by proactively identifying and reducing risks while enabling innovative product development. We constantly work towards a sustainable world-class security capability. Thirdly, we strive to be a Business Catalyst & Enabler by embodying the DNA of technical innovation and ensuring our Global Security operations are fast and agile. Heck here they even say just that: “proactively identifying and reducing risks while enabling innovative product development”. A natural part of that would be doing for example the kind of security researcher that the article of the OP is about.

Two4 2y ago

Going to need another one of these, Xe: https://xeiaso.net/shitposts/no-way-to-prevent-this/CVE-2024-4323/ https://xeiaso.net/shitposts/no-way-to-prevent-this/CVE-2024...

saagarjha 2y ago
This is not a bug caused by memory unsafe languages.
- xena 2y ago
  The only exception is if the microcode responsible for this was written in C somehow. I highly doubt it though.
  - Two4 2y ago
    Oh no, I meant that this feature was made so people could continue to use memory-unsafe languages, but it turns out to be defeatable. If only there was some way to prevent this.
- Two4 2y ago
  No, this is a feature created for memory-unsafe languages which has turned out to be yet another memory safety attack vector. But there's no way to prevent this.
  - akira2501 2y ago
    > for memory-unsafe languages And languages which require unsafe blocks to write any real system code. > But there's no way to prevent this There isn't. There are only mitigations. The environment is actively hostile. You can try to bake them in the hardware, which has huge up front design costs, and if a vulnerability is ever found, they become useless instantly. You can try to bake them into the language, which has moderate continual design costs, but if someone simply types 'unsafe' anywhere in your codebase they become useless instantly. You can try to enforce them in the frame work of your own code, which has moderate up front design costs, is possibly less reliable than the other methods, but they can be changed and redeployed when vulnerabilities are discovered. These problems don't go away simply because you made a particular hardware or language choice. You can't sweep this engineering under the rug and then act like your software is more secure than anything else.

seventyone 2y ago

"Confirmed the possibility" -- it was known when they invented this. https://infosec.exchange/@david_chisnall/112632040031740747 https://infosec.exchange/@david_chisnall/112632040031740747

halJordan 2y ago
Are you going to be posting the original shor's algorithm when the first quantum prime factorization hits the streets too?

dtx1 2y ago

> No problem, I was told, it’s not intended as a mitigation technique, it’s intended for at-scale debugging. Then certain companies decided it was a security technology. Yeah and it did work well for that usecase. https://grapheneos.social/@GrapheneOS/112066872276203917 https://grapheneos.social/@GrapheneOS/112066872276203917

gchadwick 2y ago

Does this actually have any real world implications? If you're using MTE you already know there's a simple attack that succeeds with 1/16th probability (or maybe greater if you reserve some tags for special purposes or have some exploitable pattern in how your allocator hands out tags). In that system this pushes the attack probability to 100%. A nice technique but (hopefully) you've already architectured things assuming MTE will be broken so this doesn't change anything. Certainly MTE was always pushed as a debugging feature only.

vlovich123 2y ago
> Certainly MTE was always pushed as a debugging feature only. This claim seems to come from ARM marketing but every SW company applying it - notably Google which I believe may have worked with ARM on this - mention of these types of tags in a security context (I believe Herb Sutter also talks about this as a way to harden c++ code). In fact, it’s seen as one very important way to harden existing legacy c/c++ code (and even unsafe Rust). There’s a big difference between 100% success rate and 1/16th - while you will still get an exploit through a 1/16th chance, the chances of detection raise significantly which isn’t nothing in a security context as it leaves a trail of breadcrumbs to investigate. > It will take more fundamental mitigations that address the root issue of memory corruption, like MTE, in order to dramatically raise the bar for attackers. https://googleprojectzero.blogspot.com/2024/06/driving-forward-in-android-drivers.html?m=1 https://googleprojectzero.blogspot.com/2024/06/driving-forwa... > Hardware memory tagging may fix some security pitfalls of C++, while still allowing high performance. We are looking forward to see a more broad adoption of hardware memory tagging in the future and suggest using Scan on top of hardware memory tagging to fix temporary memory safety for C++ https://security.googleblog.com/2022/05/retrofitting-temporal-memory-safety-on-c.html?m=1 https://security.googleblog.com/2022/05/retrofitting-tempora... Of course MTE + Scan described above may not be vulnerable to this attack, but my point stands that MTE is very much viewed as a memory safety hardening feature (and thus the security implications that come with safety hardening). This isn’t that bad news either. It may leave existing chips vulnerable but the next iteration of MTE will probably account for this problem (assuming you can’t patch microcode to solve this).
- 2y ago

eigenform 2y ago

The authors' hypothesis about the STLF case: > Considering the affected core (i.e., Cortex-A715) dispatches 5 instructions in a cycle [ 55], it is likely that the CPU cannot detect the dependency if the store and load instructions are executed in the same cycle, since the store information is not yet written to the internal buffers. > If Len(GAP) is 4 or more, the store and load instructions are executed in the different cycles, and the CPU can detect the dependency. Therefore, the CPU skips the tag check and always forwards the data from the store to load instructions. > If Len(GAP) is less than 4, the store and load instructions are executed in the same cycle, and the CPU fails to detect the dependency and performs the tag check for the load instruction. In this case, the forwarding is blocked on tag check faults. This would mean there's no forwarding from stores to loads within the same dispatch group on these cores?

baybal2 2y ago

[dead]