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Why Raspberry Pi Isn't Vulnerable to Spectre or Meltdown

raspberrypi.org

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Re: Why Raspberry Pi Isn't Vulnerable to Spectre or Meltdown

#41

Post by ploxiln »

tptacek wrote: post #40
ploxiln wrote: post #38

Earlier quoted context omitted.

This covers both Meltdown and Spectre. > Both vulnerabilities exploit performance features (caching and speculative execution) common to many modern processors to leak data via a so-called side-channel attack. Happily, the Raspberry Pi isn’t susceptible to these vulnerabilities, because of the particular ARM cores that we use. The reason why Spectre is not a problem is because there is no branch predictor in these si…

I'm not arguing that R-Pi's are vulnerable to Spectre.

You're arguing that this article does not cover Spectre.

It does ... it just doesn't have to fully describe spectre to show why the raspi is not affected.

Re: Why Raspberry Pi Isn't Vulnerable to Spectre or Meltdown

#42

Post by loeg »

ploxiln wrote: post #38
tptacek wrote: post #32

This is great, but remember that it covers Meltdown, not Spectre. Meltdown is the more immediate disaster, but Spectre is the more batshit vulnerability. You really want to get your head around: * The branch target injection variant of Spectre if you want to get a sense of how amazing this vulnerability is: you can spoof the branch predictor to trick a target process into running arbitrary code in its address space!…

This covers both Meltdown and Spectre. > Both vulnerabilities exploit performance features (caching and speculative execution) common to many modern processors to leak data via a so-called side-channel attack. Happily, the Raspberry Pi isn’t susceptible to these vulnerabilities, because of the particular ARM cores that we use. The reason why Spectre is not a problem is because there is no branch predictor in these si…

There is almost certainly a branch predictor even in these simple ARM cores.

Re: Why Raspberry Pi Isn't Vulnerable to Spectre or Meltdown

#43

Post by [deleted] »

Zaak wrote: post #18
tomxor wrote: post #16

Technical details aside, I find it quite amusing that the hardware in my pi zero is more secure than my desktop that is two orders of magnitude more expensive

Well, the vulnerabilities are directly connected to performance-enhancing architectural features, so...

[deleted]

Re: Why Raspberry Pi Isn't Vulnerable to Spectre or Meltdown

#44

Post by Chaebixi »

> In the good old days*, the speed of processors was well matched with the speed of memory access...Over the ensuing 35 years, processors have become very much faster, but memory only modestly so: a single Cortex-A53 in a Raspberry Pi 3 can execute an instruction roughly every 0.5ns (nanoseconds), but can take up to 100ns to access main memory.

In real-world terms, what's the fastest processor we could build today whose execution speed is reasonably matched to it's main memory access speed (so it doesn't need caches, etc)?

I could imagine that a processor, with a simple design that closely matches a naive model of how CPUs work, would be very useful for high-security applications. It would be much easier to reason about up-front.

Re: Why Raspberry Pi Isn't Vulnerable to Spectre or Meltdown

#45

Post by gaius »

Chaebixi wrote: post #44

> In the good old days*, the speed of processors was well matched with the speed of memory access...Over the ensuing 35 years, processors have become very much faster, but memory only modestly so: a single Cortex-A53 in a Raspberry Pi 3 can execute an instruction roughly every 0.5ns (nanoseconds), but can take up to 100ns to access main memory. In real-world terms, what's the fastest processor we could build today wh…

In the good old days, the speed of processors was well matched with the speed of memory access...

In fact on the Beeb, spiritual ancestor of the RPi, memory ran at 4Mhz and the CPU at only 2Mhz...

Re: Why Raspberry Pi Isn't Vulnerable to Spectre or Meltdown

#46

Post by disconnected »

tomxor wrote: post #16

Technical details aside, I find it quite amusing that the hardware in my pi zero is more secure than my desktop that is two orders of magnitude more expensive

It isn't funny or witty to point out that an Opel Corsa gets better gas mileage than a 747, even if it is factually correct.

I didn't downvote you (can't even do it), but I suspect you are getting downvoted because your analogy is so off the mark that it can't even be called "Apples vs Oranges".

edit: replying to the "why the downvotes" which has since been edited away

Re: Why Raspberry Pi Isn't Vulnerable to Spectre or Meltdown

#47

Post by ploxiln »

loeg wrote: post #42
ploxiln wrote: post #38

Earlier quoted context omitted.

This covers both Meltdown and Spectre. > Both vulnerabilities exploit performance features (caching and speculative execution) common to many modern processors to leak data via a so-called side-channel attack. Happily, the Raspberry Pi isn’t susceptible to these vulnerabilities, because of the particular ARM cores that we use. The reason why Spectre is not a problem is because there is no branch predictor in these si…

There is almost certainly a branch predictor even in these simple ARM cores.

Ah, that's good to know ... a comment below mentioned a "BTAC" (branch target access cache).

Is it just used for getting instructions into the L1i cache then?

Re: Why Raspberry Pi Isn't Vulnerable to Spectre or Meltdown

#48

Post by piinbinary »

loeg wrote: post #42
ploxiln wrote: post #38

Earlier quoted context omitted.

This covers both Meltdown and Spectre. > Both vulnerabilities exploit performance features (caching and speculative execution) common to many modern processors to leak data via a so-called side-channel attack. Happily, the Raspberry Pi isn’t susceptible to these vulnerabilities, because of the particular ARM cores that we use. The reason why Spectre is not a problem is because there is no branch predictor in these si…

There is almost certainly a branch predictor even in these simple ARM cores.

(Asking for my own edification) What does the output of branch predictor get used for in a CPU without speculation?

Re: Why Raspberry Pi Isn't Vulnerable to Spectre or Meltdown

#49

Post by Scaevolus »

blattimwind wrote: post #12

> The lack of speculation in the ARM1176, Cortex-A7, and Cortex-A53 cores used in Raspberry Pi render us immune to attacks of the sort. I didn't check, but these will almost certainly have branch prediction. What they probably lack is a predictor advanced enough to speculate on indirect branches, which AIUI is the primary vector of Spectre.

Branch prediction alone is insufficient. Speculative execution alone is insufficient. You need speculative memory loads for any of these attacks to work.

The Cortex-A53 branch predictor [1] does prefetching to keep the core fed. This ensures that the instructions are ready for decoding, but has no architectural effects beyond the L1 instruction cache, which is already a well-studied timing sidechannel.

[1]: http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc....

Re: Why Raspberry Pi Isn't Vulnerable to Spectre or Meltdown

#50

Post by Chaebixi »

gaius wrote: post #45
Chaebixi wrote: post #44

> In the good old days*, the speed of processors was well matched with the speed of memory access...Over the ensuing 35 years, processors have become very much faster, but memory only modestly so: a single Cortex-A53 in a Raspberry Pi 3 can execute an instruction roughly every 0.5ns (nanoseconds), but can take up to 100ns to access main memory. In real-world terms, what's the fastest processor we could build today wh…

In the good old days, the speed of processors was well matched with the speed of memory access... In fact on the Beeb, spiritual ancestor of the RPi, memory ran at 4Mhz and the CPU at only 2Mhz...

IIRC, some of those old machines interleaved CPU and GPU memory access windows, since memory was so much faster than CPUs back then.

Edit: this is what I'm talking about: https://www.bigmessowires.com/2011/08/25/68000-interleaved-m...:

> The Atari ST and Amiga appear to have both used a more aggressive scheme where video circuitry access occurred during known dead time in the 68000 bus cycle, so the CPU never had to wait

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