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Memory Integrity Enforcement

security.apple.com

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Re: Memory Integrity Enforcement

#91

Post by saagarjha »

randyrand wrote: post #68

> There has never been a successful, widespread malware attack against iPhone. The only system-level iOS attacks we observe in the wild come from mercenary spyware ... to target a very small number of specific individuals and their devices. Although the vast majority of users will never be targeted in this way.. Correct me if I'm wrong, but the spyware that has been developed certainly could be applied at scale at th…

It's mainly there as a swipe at Android. I don't think it really relates to the rest of the article (and, with no insight but with my conspiracy theory hat on, was included to peddle the merits of their App Store model).

Re: Memory Integrity Enforcement

#92

Post by saagarjha »

philodeon wrote: post #73

> In 2018, we were the first in the industry to deploy Pointer Authentication Codes (PAC) in the A12 Bionic chip, to protect code flow integrity in the presence of memory corruption. The strong success of this defensive mechanism in increasing exploitation complexity left no doubt that the deep integration of software and hardware security would be key to addressing some of our greatest security challenges. There hav…

> It hasn’t been a meaningful attack deterrent because attackers keep finding PAC bypasses.

Correction: it forces attackers to find PAC bypasses. They are not infinite.

Re: Memory Integrity Enforcement

#93

Post by saagarjha »

pandalicious wrote: post #80

> The presence of EMTE leaves Spectre V1 as one of the last avenues available to attackers to help guide their attacks, so we designed a completely novel mitigation that limits the effective reach of Spectre V1 leaks — at virtually zero CPU cost — and forces attackers to contend with type segregation. This mitigation makes it impractical for attackers to use Spectre V1, as they would typically need 25 or more V1 sequ…

https://mastodon.online/@ezhes_/115175838087995856

Re: Memory Integrity Enforcement

#94

Post by sfink »

pandalicious wrote: post #80

> The presence of EMTE leaves Spectre V1 as one of the last avenues available to attackers to help guide their attacks, so we designed a completely novel mitigation that limits the effective reach of Spectre V1 leaks — at virtually zero CPU cost — and forces attackers to contend with type segregation. This mitigation makes it impractical for attackers to use Spectre V1, as they would typically need 25 or more V1 sequ…

Nope. I don't know why just checking the tags during speculation wouldn't stop Spectre V1, at least for cross-type accesses? I mean, it's not that simple because your program won't crash if speculation has mismatched tags. Which means you can try as many times as you want until you get lucky. But that's certainly not a "completely novel mitigation", so I'm sure I'm missing something obvious.

Perhaps the real problem is that you can use speculation to scan large amounts of memory for matching tags, some of which would be different types, so you need something to handle that?

(talking out of my butt here)

Re: Memory Integrity Enforcement

#95

Post by saagarjha »

strcat wrote: post #86
saagarjha wrote: post #47

Earlier quoted context omitted.

Apple has been working on this for years. It's not like they started thinking about memory tagging when Daniel decided to turn it on in GrapheneOS.

GrapheneOS made our own integration of MTE for hardened_malloc and has done significant work on it. It wasn't simply something we turned on. ARM designed and built the feature which was made available in Cortex cores. Google's Tensor uses standard Cortex cores so unlike Qualcomm they didn't need to make their own implementation. Google integrated it into Android and did some work to make it available on Pixels along…

None of this is wrong but none of this really has any impact on what Apple decided to do. In fact Apple very specifically chose not to go in this direction as they describe in their blog post.

Re: Memory Integrity Enforcement

#97

Post by saagarjha »

nine_k wrote: post #77
superkuh wrote: post #30

This is the opposite of fun computing. This is commercial computing who's only use case it making sure that people can send/receive money through their computers securely. I love being able to peek/poke inside and look at my processes ram, or patch the memory of an executable. All this sounds pretty impossible on Apple's locked down systems. They're not so much general purpose computers anymore as they are locked dow…

It's all fun and games until somebody else patches the RAM of your device, and sends your money away from your account. More interesting is how to trace and debug code on such a CPU. Because what a debugger often does is exactly patching an executable in RAM, peeks and pokes inside, etc. If such an interface exists, I wonder how is it protected; do you need extra physical wires like JTAG? If it does not, how do you e…

You disable mitigations for those processes.

Re: Memory Integrity Enforcement

#98

Post by strcat »

tptacek wrote: post #22
pizlonator wrote: post #20

This is really impressive. It’s my understanding that this won’t protect you in the case where the attacker has a chance to try multiple times. The approach would be something like: go out of bounds far enough to skip the directly adjacent object, or do a use after free with a lot of grooming, so that you get a a chance of getting a matching tag. The probability of getting a matching tag is 1/16. But this post doesn’…

Even with Android MTE, one of the workarounds was probabilistic attacks on the small tag size, which imply multiple tries. One of the big distinctions here is uniform synchronous enforcement, so writes trap immediately and not on the next context switch.

It's typically used in synchronous or asymmetric mode on Android. The asymmetric mode preserves nearly the same performance as asymmetric while only having writes remain asynchronous. It's enforced once there's a read or system call. Synchronous is more important in the kernel due to how many holes there are for bypassing it, which is why GrapheneOS is using it as synchronous in the kernel and asymmetric in userspace. io_uring is a major example of how there could be a major bypass of asymmetric mode, although Android doesn't allow it for more than a few core processes. Deploying asynchronous is still useful since it's a widely distributed bug finding tool with near zero cost. The main cost is that it finds so many bugs which need to be addressed which is a barrier for deploying it for third party apps.

The main weakness is that MTE is only 4 bits... and it's not even 1/16 but typically 1/15 chance of bypassing it since a tag is usually reserved for metadata, free data, etc. The Linux kernel's standard implementation for in-kernel usage unnecessarily reserves more than 1 to make debugging easier. MTE clears the way for a more serious security focused memory tagging implementation with far more bits and other features. It provides a clear path to providing very strong protection against the main classes of vulnerabilities used in exploits, especially remote/proximity ones. It's a great feature but it's more what it leads to that's very impressive than the current 4 bit MTE. Getting rid of some known side channels doesn't make it into a memory safety implementation.

Re: Memory Integrity Enforcement

#99

Post by strcat »

achierius wrote: post #50
pizlonator wrote: post #20

This is really impressive. It’s my understanding that this won’t protect you in the case where the attacker has a chance to try multiple times. The approach would be something like: go out of bounds far enough to skip the directly adjacent object, or do a use after free with a lot of grooming, so that you get a a chance of getting a matching tag. The probability of getting a matching tag is 1/16. But this post doesn’…

The other 15/16 attempts would crash though, and a bug that unstable is not practically usable in production, both because it would be obvious to the user / send diagnostics upstream and because when you stack a few of those 15/16s together it's actually going to take quite a while to get lucky.

Typically 14/15 since a tag is normally reserved for metadata, free data, etc. Linux kernel reserves multiple for the internal kernel usage since it was introduced upstream as more of a hardware accelerated debugging feature even though it's very useful for hardening.

Re: Memory Integrity Enforcement

#100

Post by strcat »

saagarjha wrote: post #95
strcat wrote: post #86

Earlier quoted context omitted.

GrapheneOS made our own integration of MTE for hardened_malloc and has done significant work on it. It wasn't simply something we turned on. ARM designed and built the feature which was made available in Cortex cores. Google's Tensor uses standard Cortex cores so unlike Qualcomm they didn't need to make their own implementation. Google integrated it into Android and did some work to make it available on Pixels along…

None of this is wrong but none of this really has any impact on what Apple decided to do. In fact Apple very specifically chose not to go in this direction as they describe in their blog post.

The side channel fixes and new MTE instruction features are not specific to Apple. Apple's blog post has some significant misleading claims and omissions. It's marketing material, not a true technical post without massive bias. It's aimed at putting down the existing deployments of MTE, hyping up what they've done and even downplaying the factually widespread exploits of Apple devices which are proven to be happening. If they're not aware of how widespread the exploits of their devices are including by low level law enforcement with widely available tools, that's quite strange.
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